bluuebunny/crossref_metadata_2025 huggingface dataset:
A Novel Concept of Flexible Pipe End Fitting: Tensile Armor Foldless Assembly
Authors: Campello George , Bertoni Fabiano , de Sousa José Renato M. , Carpigiani Marcos , Vardaro Eduardo , Mudry Guillermo
Published: August 2013

The structural behavior of the flexible pipe tensile armors inside the end fitting (EF) is different from the one observed in the pipe body. The actual design methodology shows that the end fitting of the riser top section (at the interface with the floating unit) is critical with respect to fatigue, as stress concentration that occurs in this region during the end fitting assembly leading to significant plastic strains.

Aiming at improving the structural performance of flexible risers, Petrobras designed and patented a novel concept of flexible pipe end fitting in which its assembly can be carried out without the need of folding the tensile armor thus avoiding the introduction of plastic strains and residual stresses in this layer.

In order to assess and quantify the benefits of this new concept, in this work, a comparative study between the current end fitting concept used by the industry and the new technology proposed by Petrobras was conducted. This study comprises not only the stress distribution along the wire inside the end fitting but also the fatigue performance. For this purpose, finite element analyses have been carried out considering the entire end fitting mounting process and also the operational loads.

These analyses were calibrated with results from midscale tests in which a longitudinal slice of the real end fitting was simulated. An instrumented tensile armor wire was embedded in the resin epoxy and pulled out from a test device.

The results obtained show that the using of the proposed technology results in a considerably end fitting fatigue performance improvement.
Modeling of the Collapse and Propagation Behavior of UOE SAW Pipes Under External Pressure: Influence of Thermal Treatments for Typical Coating Applications
Authors: Mantovano Luciano O. , Serebrinsky Santiago , Ernst Hugo A. , Perez Teresa , Valdez Martin , de Souza Marcos , Chad Luis C.
Published: August 2013

Large diameter UOE pipes are being increasingly used for the construction of offshore pipelines. Since oil discoveries are moving towards ultra deep water areas, collapse resistance is a key factor in the design of the pipelines. It has been demonstrated in previous works that the application of typical coating thermal treatments increases the collapse resistance of the pipes recovering the original strength of the plate. To improve the understanding of these effects, the Tenaris has embarked on a program of both, experimental testing and finite element modeling.

Previous phases of this work formulated the basis for model development and described the 2D approach taken to model the various stages of manufacture, from the plate to the final pipe and the collapse test. More recent developments included some modeling enhancements, sensitivity analyses, and comparison of predictions to the results of full scale collapse testing.

In the present work, 3D finite element analyses of collapse were performed and compared with the latest collapse and propagation tests performed by Tenaris, where the effect of typical coating thermal treatments was studied and significant increments in the collapse pressure of pipes were obtained. The numerical results show a good agreement with the experimental ones and could predict the increment produced in the collapse pressure by the effect of the thermal treatments. Comparison of the results with the predictions from API RP 1111 and DNV OS-F101 equations was also performed.

The outcomes of this study will be employed to further optimize the collapse resistance of subsea linepipe in order to reduce material and offshore installation costs through the increment of the fabrication factor as stated in the DNV OSF101 standard.
Cross-Sectional Layout Analysis of Steel Tube Umbilical
Authors: Lu Qing-zhen , Yue Qian-jin , Yang Zhi-xun , Wang Gang , Yan Jun , Qu Yan
Published: August 2013

The paper presents four different layouts of a subsea steel tube umbilical which is composed of six steel tubes, three electrical cables and one optical fiber cable. When the umbilical is loaded, there will be a relatively large stress and deformation when the cross-sectional layout is unreasonable. So the principles of the cross-sectional layout of the umbilical are studied considering the stress and deformation of components. The contact stress between components, stress and deformation of components are analyzed and compared based on finite element method. The preferable design of cross-sectional layout for this umbilical is present.
Safety Factors for Fatigue Analysis of Flexible Pipes Based on Structural Reliability
Authors: dos Santos Loureiro Filho Fernando , de Lima Edison Castro Prates , Sagrilo Luís Volnei Sudati , de Sousa Fernando Jorge Mendes , de Lemos Carlos Alberto Duarte
Published: August 2013

Structural reliability–based methodology [1,2] has been proposed for fatigue analysis of flexible pipes tension armours. In this methodology a design criterion is verified using a standard reliability analysis approach and checking if the fatigue failure probability is equal to or less than a target value. The use of reliability analysis in the every day design practice is not yet a common procedure. Hence, in this paper we present the calibration of safety factors for Brazilian environmental conditions to be used in the standard fatigue analysis of flexible riser tension armours. The calibration is performed in order to guarantee the same target probability of failure. The safety factors are calibrated considering four flexible risers, two connected to FPSOs and the other two to semi-submersibles located in different water depths in Campos Basin offshore Brazil.
Methodology for Wind/Wave Basin Testing of Floating Offshore Wind Turbines
Authors: Martin Heather R. , Kimball Richard W. , Viselli Anthony M. , Goupee Andrew J.
Published: August 2013

Scale model wave basin testing is often employed in the development and validation of large scale offshore vessels and structures by the oil and gas, military and marine industries. A basin model test requires less time, resources and risk than a full scale test while providing real and accurate data for model validation. As the development of floating wind turbine technology progresses in order to capture the vast deepwater wind energy resource, it is clear that model testing will be essential for the economical and efficient advancement of this technology. However, the scale model testing of floating wind turbines requires one to accurately simulate the wind and wave environments, structural flexibility and wind turbine aerodynamics, and thus requires a comprehensive scaling methodology.

This paper presents a unified methodology for Froude scale testing of floating wind turbines under combined wind and wave loading. First, an overview of the scaling relationships employed for the environment, floater and wind turbine are presented. Afterward, a discussion is presented concerning suggested methods for manufacturing a high-quality, low turbulence Froude scale wind environment in a wave basin to facilitate simultaneous application of wind and waves to the model. Subsequently, the difficulties of scaling the highly Reynolds number-dependent wind turbine aerodynamics is presented in addition to methods for tailoring the turbine and wind characteristics to best emulate the full scale condition. Lastly, the scaling methodology is demonstrated using results from 1/50th scale floating wind turbine testing performed at MARIN’s (Maritime Research Institute Netherlands) Offshore Basin which tested the 126 m rotor diameter NREL (National Renewable Energy Lab) horizontal axis wind turbine atop three floating platforms: a tension-leg platform, a spar-buoy and a semi-submersible. The results demonstrate the methodology’s ability to adequately simulate full scale global response of floating wind turbine systems.
Finite-Memory Nonlinear System Modelling of Offshore Structural Response Accounting for Extreme Values Residues
Authors: Mallahzadeh H. , Mohd Zaki N. I. , Husain M. K. Abu , Najafian G.
Published: August 2013

Offshore structures are exposed to random wave loading in the ocean environment, and hence the probability distribution of the extreme values of their response to wave loading is of great value in the design of these structures. Due to nonlinearity of the drag component of Morison’s wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of the probability distribution of extreme responses are not available. Monte Carlo time simulation technique can be used to derive the probabilistic properties of offshore structural response, but the procedure is computationally demanding. Finite-memory nonlinear system (FMNS) modeling of the response of an offshore structure exposed to Morison’s wave loading has been used to reduce the computational effort, but the predictions are not always of high accuracy. In this paper, further development of this technique, which leads to more accurate estimates of the probability distribution of the extreme responses, is reported.
Stability Evaluations of Semi-Submersible Heavy Transport Vessels by a Progressive Flooding Simulation Tool
Authors: Dankowski Hendrik , Hatecke Hannes
Published: August 2013

Rising needs for heavy transport operations are intensified by the expanding offshore industry worldwide. Whenever very large and heavy objects have to be transported, only semi-submersible heavy transport vessels are capable of carrying this special cargo. Accidents in the past during operations of these vessels highlight the requirement of analyzing the operation procedures in more detail. Especially the submerging process of the main working deck is very critical regarding the hydrostatic stability. A new numerical progressive flooding simulation method will be presented for applications like accident investigations or damage stability assessments. This method is modified to fit the special requirements of simulating the operational behavior of semi-submersible vessels in the time-domain. A direct approach is chosen, which computes the flux between the compartments based on the Bernoulli equation and the current pressure heads at each intermediate step. Losses due to viscous effects are taken into account by empirical discharge coefficients. This method will be used to simulate the submerging operation in the time-domain to point out critical situations regarding the stability of the vessels and the cargo. This will be compared to accidents which occurred in the past. Furthermore, recommendations for operational procedures are proposed.
Practical Considerations for the Structural Analysis of Offshore Topside Structures Under Gas Explosion Accidents
Authors: Han Dae Suk , Kim Gyusung , Sim Woo Seung , Jang Young Sik , Shin Hyun Soo
Published: August 2013

Gas explosion accidents have been recognized as a major hazard of offshore facilities in oil & gas industries. Due to the nature of offshore topside structures, even a single collapse of structural members or equipments may lead to enormous economic and environmental losses. Therefore, such potential hazards that cause the accidental collapse need to be evaluated closely. Gas explosion has been categorized as an important issue of the design of offshore structures regarding the severity of the accident.

This paper presents practical considerations for the nonlinear dynamic structural analysis of offshore structures under blast loadings from gas explosion accidents. Numerical investigations including modeling of blast loads and idealization of structural materials and members have been conducted for the overall topside structures. As a design step for offshore structures under blast loadings, an applicable guidance on the finite element analysis (FEA) is described in this study.
Experimental Analysis of Surface Geometry, External Damping and Waves on Semisubmersible Vortex Induced Motions
Authors: Martin Bruce , Rijken Oriol
Published: August 2013

Semisubmersible Vortex Induced Motions have been studied extensively at model scales, and observed under field conditions. VIM response is of particular concern in evaluations of Steel Catenary Riser (SCR) fatigue damage. Historically, most of this experimental work was done with bare models, without much effort to represent actual hull surface characteristics. In this paper, the effect of these appurtenances, tow direction and wave action is investigated. There is also an examination of vortex induced yaw response. VIM response is assessed using motion trajectories, dominant response direction, and amplitudes and periods of response. Variations in these quantities are also investigated.
A Case of Sinkage of a 34” Gas Pipe During Pull-in Operation, São Paulo, Brazil
Authors: Maria Paulo Santa , Maciel Raquel , Martins Ian
Published: August 2013

The objective of this paper is to provide information aiming at a better understanding of the mechanisms that led to the sinkage of a gas pipe during a pull-in operation, also performing a survey of all relevant information regarding this operation and soil investigation. This study also comprises an analysis of the available soil information and the identification of possible scenarios of behaviour to feed mathematical models. A first mathematical model was developed to assess the axial horizontal force Q that causes a horizontal closed end pipe of diameter D and length ℓ to move inside a sandy soil mass when buried at a depth z. Further on, two feasible mechanisms were studied to explain the pipe sinkage during the pull-in operation. The first mechanism was associated with compressive volumetric strains that take place within the sand layer beneath the pipe. These strains are accounted for the relative soil-pipe shearing displacements. The second mechanism assumes that the soil beneath the pipe is submitted to a plastic failure under a vertical load corresponding to the vertical component of the pulling force applied to the pipe-head. This model comprises an elastic pipe resting on a rigid-plastic soil that fails under Mohr-Coulomb envelop of failure. Lack of soil information, however, hampered the full understanding of the process that led to the sinkage of the pipe.
Analysis of Stress Levels and Indication of Ruptures of Flexible Pipes Tensile Armor Wires During a Fatigue a Dynamic Tension to Tension Test
Authors: Lopes Diogo , Souza Italo , Falcao Gelson , Clevelario Judimar , Sheldrake Terry
Published: August 2013

Flexible pipes are widely used in the exploration of oil at ultra-deepwater depths due to their properties of resistance to bending forces and ease of installation, compared to rigid pipe lines.

For each specific service application, several tests are required to qualify the flexible pipe’s design. One of the most important is the dynamic tension to tension test, the purpose of which is to qualify the end fitting assembly procedure and evaluate the design methodology used to predict the pipe’s service life.

During the development of the test, several sensors were fitted to the pipe sample to monitor the behavior of the armor wires. In order to monitor this test and identify any possible failure of the tensile armor wires, strain gauges were applied to all the wires of the external tensile armor layer in the area outside of the end fittings. Additionally, strain gauges were also applied to some of the internal and external tensile armor layer wires inside the end fittings. Other sensors, such as inclinometers and a tri-axial accelerometer were also applied to the pipe sample.

Analyses of the signals from the test sample instrumentation enabled detection of rupture of the tensile armor wire while instrumentation redundancy confirmed the tensile armor wire’s failure.

This paper presents the methodology used to identify the first 5 tension armor wire ruptures, which were identified by some of the sensors, i.e., the accelerometer, the inclinometer, and the strain gauges together with a comparison of the data of all the wire ruptures during the test.
Collapse Estimation of Interlocked Armour of Flexible Pipe With Strain Energy Equivalence
Authors: Tang Ming-gang , Yan Jun , Wang Ye
Published: August 2013

Deepwater environment brings unbonded flexible pipelines with collapse risk of interlocked armours, such as pressure armour and carcass. An effective and accurate prediction for collapse is required in design process.

This paper presents a theoretical approach for estimating collapse of the interlocked armours based on strain energy equivalence principle of representative volume method. The strain energy with Dirichlet boundary is calculated using FEA software for the armours, which usually have complex cross-section. Meanwhile, an equivalent ring model is established as the representative volume, of which strain energy is acquired analytically. Equivalent thickness can be obtained by equivalence of both the two energys. And then the resistance to collapse of the flexible pipe can be carried out directly.

Theoretical results from the approach presented in the paper are compared with numerical results proved by experimental ones from reference, which verifies the equivalence approach. This approach provides a new angle to process parametric design for critical collapse of the flexible pipe.
Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Commissioning and Preliminary Validation
Authors: Simos Alexandre N. , Tannuri Eduardo A. , da Cruz José J. , Filho Asdrubal N. Queiroz , da Silva Bispo Iuri B. , Carvalho Rafaella C. A.
Published: August 2013

This paper addresses the development, installation and initial tests of a system for wave spectra estimation from the measurements of the first order motions of a moored FPSO located in Campos Basin, Brazil. The estimation is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform, and this information is sent to a remote data-base, also accessed by the wave-estimation system. The algorithm also requires the Response Amplitude Operators (RAOs), and they depend on the loading conditions of the FPSO.

A previous analysis considering typical loading configurations of the tanks showed that the wave estimation is mainly dependent on the total displacement of the vessel, and not on the load distribution among the tanks. Hence, the RAOs for the full-range of drafts (or total displacements) were numerically generated, considering a uniform distribution of the load among the tanks. Since the draft of the platform was not directly measured, the loading levels of the tanks are obtained from the automation system of the platform, and the draft is then estimated. Finally, the heading is measured by a gyrocompass, and it is necessary for the definition of the global wave direction. The Bayesian estimation is executed at time-spans of 30min. A parametric optimization algorithm is then applied for the calculation of the wave spectrum parameters from the raw-spectrum obtained by the Bayesian estimation.

A user-friendly interface was also developed, with on-line information about platform motions, estimated wave spectrum, peak statistics and data history. Since all information is accessed by network, the wave system can be installed either on-board or in the on-shore monitoring center.

The system was commissioned and a partial 3-month validation campaign was executed. The spectrum results were compared to NOAA estimates. As expected, low-period wave components (smaller than 8s) could not be estimated with accuracy, since the FPSO presents small motion response for these components. Swell and high-period wave components estimates presented good qualitative and quantitative agreement with satellite prediction.
Interference Resistance of Multi-Hull Vessels in Finite-Depth Waters
Authors: Aubault Alexia , Yeung Ronald W.
Published: August 2013

As high-speed ferry traffic is growing in near-shore areas, fuel efficiency of vessel operating in finite-depth waters becomes more critical. This can be achieved by introducing multi-hulls and minimizing the wave resistance by a proper configuration of the hulls. The wave resistance of thin-hulled vessels can be computed within Michell’s theory. Based on this principle, Yeung et al. (2004) introduced a formulation of the interference wave resistance on multi-hull vessels in deep water, after linearization of the boundary conditions. The method is generalized to any water-depth in this paper. Havelock (1921) derived the wave resistance of a single-hull vessel in finite-depth water. An expression of the interaction resistance between two hulls in finite-depth waters is derived, using a distribution of Havelock sources on the hulls. It is shown that the interference resistance may be defined as a function of geometric variables and a length-based Froude number and depth-based Froude number. The effect of sub-criticality, criticality and supercriticality of depth-based Froude number on the interference resistance is explored. The computation of the total wave resistance of two hulls is extended to vessels with any number of hulls. The application of this solution method is demonstrated. With the use of the formulation, multi-hull designs are optimized with respect to the geometric distribution of hulls as well as forward speed and water depth. The design of multi-hull vessels illustrates how an optimized design is quickly obtained. Design decisions early in the design process can therefore be facilitated by this procedure.
AUV Guidance System for Subsurface Ice Intelligence
Authors: Scibilia Francesco , Jørgensen Ulrik , Skjetne Roger
Published: August 2013

This paper considers an AUV guidance system for subsurface ice intelligence. A topologically organized neural network model is used to represent the operating environment. The dynamics of each neuron, characterized by a shunting equation, are used to represent the local environmental information. Targeted areas have the highest values. The AUV moves from areas with low dynamics to areas with higher dynamics like in a potential field navigation. The kinematic constraints of the AUV are taken into account by using Dubins theory to generate feasible paths.
Recent Experience in the Lateral Buckling Design of Medium to Large Diameter Pipelines
Authors: Branković Maša , Anderson Benjamin , Shim Edwin , Zeitoun Hammam , Chin Eu Jeen
Published: August 2013

In the last decade and a half, the pipeline industry has gained significant experience in both the design and operation of pipeline systems exposed to lateral buckling. JIPs, design guidelines and recommended practices such as SAFEBUCK (Reference [1]), HOTPIPE (Reference [2]) and DNV RP-F110 (Reference [3]), together with operational feedback have significantly contributed to the development of comprehensive methods to determine robust lateral buckling design solutions. Most of this knowledge has been gained from understanding the behaviour of HP/HT (high pressure/ high temperature) small, light diameter systems, which buckle more predictably at operating conditions well below design conditions. Medium to large diameter, concrete coated pipelines are generally considered to be less prone to lateral buckling by comparison (due to expected milder design conditions), however the consequence of their buckling is far more severe and can prove extremely difficult to control.

Fundamentally, the knowledge acquired and general lateral buckling design methodologies developed for HP/HT systems can be applied for the design of larger, heavier pipelines, however there are a number of key differences in the behaviour of both systems which warrant special considerations.

Key considerations include (a), effective axial force and critical buckling force development (impacting susceptibility and initiation considerations), (b) severe post-buckle response on-seabed (impacting the acceptance of uncontrolled buckling for definition of buckle trigger spacing and extents), and (c), the consequence of introducing buckle triggers. Additional design complexity is introduced for systems installed in shallow water, which are exposed to more severe metocean conditions than deepwater HP/ HT systems. This requires heavy concrete weight coating (CWC) for stabilisation, resulting in strain localisation at field joints, concrete stiffening effects and complex interaction with hydrodynamic loading, typically ‘competing against’ intuitive global buckling design.

All of the above factors result in lateral buckling design solutions for medium to large diameter, concrete coated pipelines becoming rather challenging.
Natural Resource Exploration With Sonar on Underwater Vehicle
Authors: Sawa Takao , Kasaya Takafumi , Hyakudome Tadahiro , Yoshida Hiroshi
Published: August 2013

Occurring as a set of 17 chemical elements in the periodic table, rare earth elements such as neodymium are necessary for the development of mobile phones and magnet motors. Although securing rare earth elements is essential for economic growth of all nations, their demand is rapidly expanding among global powers such as Brazil, Russia, India, and China. Rare earth element deposits were discovered in the seafloor near hydrothermal vents in the 1980s. Japan has the sixth largest exclusive economic zone (EEZ) and is abundant in underwater natural resources such as a cobalt and a manganese mine. Because underwater exploration of rare earth elements was deemed unprofitable, the practice was suspended. Current advancements in underwater robotics, however, have led to economic viability in this venture. Such developments have resulted in the increased use of remote sensing with sonars on unmanned underwater vehicles.

The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed a cruising autonomous underwater vehicle (AUV) known as Urashima. This AUV performed its first sea trial in 2000, and cruise for 317 km without recharging or refueling in 2005 as a world record at the time. The first mission of Urashima was a vast sea exploration to investigate worldwide environmental crises such as global warming. However, the purpose of these missions has since then shifted primarily to the exploration of underwater natural resources. In addition, JAMSTEC developed a synthetic aperture sonar on a neutral buoyancy towfish in 2010. This underwater exploration system, known as Kyouryuu, scanned Wakamiko caldera at the sea bottom in Kagoshima Bay where volcanic activity was evident. Numerous hot-water flows from hydrothermal vents were clearly recorded. In addition, many dormant chimneys were detected. These features provide important data for estimating the distribution of hydrothermal vents and chimneys in addition to their transitions.
A Coupled Finite Difference and Weighted Least Squares Simulation of Violent Breaking Wave Impact
Authors: Lindberg Ole , Bingham Harry B. , Engsig Karup Allan Peter
Published: August 2013

Two model for simulation of free surface flow are presented. The first model is a finite difference based potential flow model with non-linear kinematic and dynamic free surface boundary conditions. The second model is a weighted least squares based incompressible and inviscid flow model. A special feature of this model is a generalized finite point set method which is applied to the solution of the Poisson equation on an unstructured point distribution. The presented finite point set method is generalized to arbitrary order of approximation. The two models are applied to simulation of steep and overturning wave impacts on a vertical breakwater. Wave groups with five different wave heights are propagated from offshore to the vicinity of the breakwater, where the waves are steep, but still smooth and non-overturning. These waves are used as initial condition for the weighted least squares based incompressible and inviscid model and the wave impacts on the vertical breakwater are simulated in this model. The resulting maximum pressures and forces on the breakwater are relatively high when compared with other studies and this is due to the incompressible nature of the present model.
On the Axial-Flexural-Torsional Coupling of Underwater Slender Cylinders
Authors: Pinto Waldir T. , Levi Carlos A.
Published: August 2013

This paper presents a numerical model for the simulation of the axial-flexural-torsional coupling of undewater cylindrical structures. Cylindrical structures are largely utilized in the marine environment in a wide range of applications as in risers, marine cables, flexible pipes, mooring systems and so on. They may exhibit complex axial-flexural-torsional coupling, which makes the structural analysis highly nonlinear. In addition, the fluid-structure interaction may include flow induced vibrations, frequency lock-in and internal flow effects. The proposed three-dimensional model assumes that the structure aspect ratio is very high, its cross section is circular, the cable is elastic and may experience large displacements and large strains, as long as the elastic regime holds. The steady state load on the cylinder consists of the self-weight and buoyancy, drag and lift forces, in addition to a distributed residual twist along the cylinder. The drag and lift forces are evaluated by Morison type formulation. The governing differential equations are derived from first principles, assuming Newtonian mechanics. Then, they are solved numerically by a finite element formulation based on nonlinear space frame elements. The resulting set of algebraic equations is solved by a minimization technique that uses the Newton-Raphson algorithm. Results show the ability of the model to predict the static configuration of equilibrium of the cylinder and to capture the coupling between axial, flexural and torsional responses of the cylinder.
Ultra Heavy Wall Linepipe X65: Full Scale Severe Straining Sequences of Pipeline Strings
Authors: Di Vito Luigi , Lucci Antonio , Amato Stefano , Mannucci Gianluca , Tintori Federico , Crippa Stefano , Giugliano Paolo , Armengol Mariano , Darcis Philippe , Ruiz Eduardo , Pelcastre Mauricio , Mota Noé , Quintanilla Héctor
Published: August 2013

Tenaris and Centro Sviluppo Materiali (CSM) are carrying out a Joint Industrial Project aimed at developing heavy wall line pipes. The suitability for very severe applications, involving high service pressures and temperatures, the latter causing large strain fluctuations, in presence of an aggressive sour environment, is analyzed both theoretically and experimentally, including small and full pipe models and tests.

The full project program aims at developing a new generation heavy wall product, supported by a comprehensive laboratory analysis of the material response under severe mechanical loading in aggressive environment and a full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to basic understanding of impact on design criteria of interaction between severe loading and aggressive environment. Four papers, [2], [3], [4] and [5], have been already presented, in previous OMAE conferences, on this project.

The present paper focusses on the full scale testing performed on strings of pipeline consisting of different pieces of pipe. In particular, two full scale testing have been performed applying the severe straining sequence defined as extreme in term of resistance against ratcheting, also involving plastic straining, as deduced in a previous work inside the project. The loading sequence was applied in global strain control, averaged on the whole string length, but necessarily the local distributions of strain differs in the three pieces of pipe. Analytical considerations are done about the expected straining behaviour and experimental results confirmed the theoretical considerations. The high strain hardening capability of the X65 steel pipes, metallurgically designed for strain based applications, guaranteed a good recovery of any non-homogeneity in straining, both during cycling that in larger axial deformation of the string.

During severe cycling in elastic-plastic regime in presence of pipe internal pressure, the strings demonstrated good resistance to ratcheting. In fact, due to the material capability to redistribute the cycling strains along the whole sample length, any section experienced limited ratcheting with unreversed circumferential expansion, during cycling, well within limits of tolerability. It is worth noting that, even in presence of severe cycling conditions, both on-shore type girth welds (SAW for double joint) and off-shore type (GMAW in Narrow Groove Bevel Preparation) preserved their integrity with no cracking or other damage.
Structural Reliability Applications in Design and Maintenance Planning of Ships Subjected to Fatigue and Corrosion
Authors: Câmara Marcos Corrêa , Cyrino Júlio C. Ramalho
Published: August 2013

This paper presents structural reliability applications in design and maintenance planning for ships hull structures. For the assessment of structural strength, the model developed consists in an ultimate limit-state of hull-girder considering degradation by corrosion based in a statistical investigation of time-variant hull girder strength made by ABS (American Bureau of Shipping) on 2007. The time dependent reliability index obtained with the minimum elastic section modulus required by the rules of the classification society American Bureau of shipping (ABS), of two ship designs are compared against the results obtained from the target reliability index based design. The target reliability index assessment for corroded hulls is also showed. The monte-carlo simulation reliability method is used to calculate the time-dependent reliability of the primary hull structure.

Two approaches of fatigue and corrosion-enhanced fatigue time dependent reliability are developed. A long term stress range applied to a detail is fitted to a weibull distribution based in a known design life. A utilization factor is introduced in order to consider the fraction of time at sea. A risk-based inspection planning is discussed for commercial and naval vessels Both S-N curve and fracture mechanics based reliability methods are used and the results are compared. An example of reliability updating after a inspection result is showed.
Using a Simplified Smoothed Particle Hydrodynamics Model to Simulate Green Water on the Deck
Authors: Pakozdi Csaba , Stansberg Carl-Trygve , Skjetne Paal , Yang Wei
Published: August 2013

Severe storms have gained more attention in recent years. Improved metocean data have led to new insight into severe wave conditions for marine design. Therefore, there exists an industrial demand for fast and accurate numerical tools to estimate the hydrodynamic loads during e.g. green water events.

Model tests generally play an important role in these studies. In the recent past, several practical engineering tools have also been developed, based on the experience from the experimental data bases in combination with simplified but still theoretical formulations. One such tool is Kinema2, which is based on non-linear random wave modeling combined with 3D linear diffraction theory to initially identify green water events, and then finally apply a simplified water-on-deck and slamming load estimation. This forms the background for the work presented in this paper which shows the feasibility of a new technique based on the Smoothed Particle Hydrodynamics (SPH). This method can give more detailed forecast of the hydrodynamics on the deck than the simplified water-on-deck estimation. SPH uses a Lagrangian framework (particles) to describe the fluid dynamics. The water propagation and kinematics of the green water events are, in this introductory stage of the study, reproduced by using a SPH inlet condition where particles are injected with given velocity from a curved rectangular area against the deck and the deckhouse. The relative wave height and water particle velocities found from KINEMA2. Numerical results for water elevation and velocity on deck are compared against model test time series and previous results from other numerical simulation methods. The present Lagrangian nature (compared to traditional Eulerian-VOF methods) can in principe significantly reduce the CPU demand and increase the simulation speed. Slamming pressures can then be calculated e.g. from simple slamming formula calculations. In principle, pressures can also be found directly from the SPH calculations, while this would demand a significantly larger number of particles which increases CPU demand of the SPH method.
Response Based Identification of Critical Wave Scenarios
Authors: Clauss Günther F. , Klein Marco , Soares Carlos Guedes , Fonseca Nuno
Published: August 2013

In the last years the identification and investigation of critical wave sequences regarding offshore structure responses became one of the main topics in the ocean engineering community. Thereby the area of interest covers the entire field of application spectra at sea — from efficient and economic offshore operations in moderate sea states to reliability as well as survival in extreme wave conditions. For most cases, the focus lies on limiting criteria for the design, such as maximum global loads, maximum relative motions between two or more vessels or maximum accelerations, at which the floating structure has to operate or to survive. These criteria are typically combined with a limiting characteristic sea state (Hs, Tp) or a rogue wave. For the investigation of offshore structures as well as the identification of critical wave sequences, different approaches are available — most of them are based on linear transfer functions as it is an efficient procedure for the fast holistic evaluation. But, for some cases the linear method approach implies uncertainties due to nonlinear response behavior, in particular in extreme wave conditions.

This paper presents an approach to these challenges, a response based optimization tool for critical wave sequence detection. This tool, which has been successfully introduced for the evaluation of the applicability of a multi-body system based on the linear method approach, is adjusted to a nonlinear task — the vertical bending moment of a chemical tanker in extreme wave conditions. Therefore a nonlinear strip theory solver is introduced into the optimization routine to capture the nonlinear effects on the vertical bending moment due to steep waves acting on large bow flares. The goal of the procedure is to find a worst case wave sequence for a certain critical sea state. This includes intensive numerical investigation as well as model test validation.
On the Further Optimization of the “Green Water Concept” for Wave Energy Conversion
Authors: Helder Joop A. , Schmittner Christian , Buchner Bas
Published: August 2013

This paper presents initial results from the following-up study of the ‘inverse’ or ‘green water concept’ for wave energy conversion. Initially presented in 2009, the ‘inverse concept’ was developed by MARIN as a vehicle for open discussion and exchange of ideas in the field of wave energy conversion. Pilot model tests presented in 2010 showed the great potential of the concept, but also revealed the challenges associated with Power Take Off design.

The present study aims to further optimize the inverse concept. A new PTO system has been incorporated, based on robustness and effective use of the structure’s (de)optimized hull. The resulting renewed concept combines maximized vessel motions with OWC-type of wave energy conversion.

This paper focuses on the motion response of the renewed concept. Frequency domain calculations show the response of the concept with water columns (moonpools) at the bow and stern. Remarkably, the already maximized motions of the hull become even more extreme when moonpools are incorporated. Special attention is given to the relative motions of the water inside the moonpools, as these give an indication of the wave energy conversion potential of the concept. The relative water motions inside the moonpools show a large response that is characterized by multiple peaks. This indicates the concept’s ability to convert energy in a wide range of sea states.

Results from additional diffraction analysis show that through proper tuning, the water columns inside the moonpools can be modeled as solid water-bodies. This allows for a future numerical modeling of the hydrodynamic interaction between structure, water columns, entrapped air and PTO damping in the time domain.
Targeting the Wave Resource From the Power Take-Off Perspective
Authors: MacCready Tyler , Paulos James , Zambrano Thomas
Published: August 2013

Frequency dependence in a power take-off mechanism means that power generated does not have a one-to-one correspondence with power available in the waves. Viewing wave power resources from the perspective of the power takeoff device leads us to question the assumption that waves carrying the maximum power are the best target for resource development. We explore this power take-off perspective for a heave device fitted with an electric generator and find that power is preferentially produced from higher frequency waves.

While globally most wave power is concentrated in low frequency swells, when power production is dependent on velocity, as when driving an electrical generator, an energy-harvesting device gathers more power from higher frequency waves. We examine spectral data from the Pacific Ocean and the Gulf of Mexico and find that the peak frequency for heave velocity, and hence for power production, can be as much as twice the peak frequency of the resource power in the waves.

Furthermore, Response Amplitude Operator (RAO) considerations demonstrate the need for small, ‘nimble’ devices to access the most easily available wave power. We compare the total energy capture from the empirical wave spectra using devices tuned to different natural frequencies and find the most energy is captured, regardless of geographic location, with devices that have natural frequencies around 0.2 Hz, far above the swell frequency.
Hydrodynamic Modelling for Dynamic Positioning and Maneuvering Controller Design
Authors: Refsnes Jon , Sørensen Asgeir J.
Published: August 2013

In this paper we present a new approach for mathematical modeling of hydrodynamic drag and lift forces and moment of marine vessels for the purpose of model-based control in the horizontal plane spanned by the surge, sway and yaw degrees of freedom (DOFs). Simplified low-fidelity models are proposed satisfying strict real-time computing requirements. The proposed control plant models are particularly suitable for the use in real-time simulation-based design and testing of dynamic positioning (DP) and maneuvering control systems. Moreover, the proposed equations may be suitable for a wider range of both underwater vehicles and surface vessels. The main idea is to employ conventional rudder theory, consider the vehicle as a large lifting surface similar to slender body theory, and, finally, transform the equations into the body-fixed reference frame. It will be shown that only moderate modifications to standard rudder equations are needed to derive the total hydrodynamic damping in surge, sway and yaw. Full scale experimental test results are presented showing that the proposed drag and lift models match the actual forces to a large extent.
Numerical Simulation of the Added Mass of the Fluid Adjacent to the Ship Hull in Vibration Measured During Sea-Trials in Tanker Ships to be Converted to Offshore Construction Vessel
Authors: Silva Neto Severino Fonseca , Figueiredo Silvia Ramscheid , Tapia Reyes Marta Cecilia , de Mesquita Ortiz Luiza
Published: August 2013

This study aims to analyze the influence of the kinetic energy of the fluid adjacent to the hull of a tanker ship in its vertical vibration frequencies, comparing them with experimental measurements obtained during sea-trials. The one-dimensional modeling of ships allows the construction of simple finite element models from the structural elements of its master section, with structural and added masses, and their frequencies are verified by full-scale measurements, during the sea-trials. The numerical results of these models, with the value of the effective shear area as a fraction of the total area of the strength steel are compared to those obtained in full-scale measurements during sea trials of an oil tanker to be converted to Offshore Construction Vessel. Global vibration measurements were carried out in two of the six ships with the same hull. Accelerometers were installed in eleven strategic points of each hull. Vibration data acquisition was performed simultaneously for these locals in thirteen rotations of the main engine. The amplitude spectra of vibration velocity on the frequency range of measurements were obtained and were plotted graphs of the evolution of the main harmonics, depending on the rotation of the main engine, in order to identify four natural frequencies of the overall vibration of the hull, which were compared to the numerical model. The calculation is performed by the added mass formulations from Burrill, Todd, Kumay and Lewis/Landweber [8] curves, including in all three-dimensional effect by Townsin [17] coefficients, which is checked against the experimental results. The comparison between numerical and experimental results allows assessing the influence of the kinetic energy of the fluid surrounding the hull in the natural frequencies of vibration of the numerical model of the tanker ship and simulating their dynamic behavior after conversion in Offshore Construction Vessel.