bluuebunny/crossref_metadata_2025 huggingface dataset:
Rayleigh Damping Effects on Global Analysis of Umbilicals
Authors: da Silveira Lauro Massao Yamada , Tanaka Rafael Loureiro , Novaes Joa˜o Paulo Zi´lio
Published: November 2011

Despite global analysis of umbilicals is a well-known area in the offshore systems design, some topics are still opened for discussions. One of these topics refers to the structural damping. Obviously, the viscous damping caused by hydrodynamic drag forces is the major source of damping to the whole system. However, in some severe load cases, the host vessel dynamics may induce high snatch loads to the umbilical top end and these loads are more related to structural damping, specifically in tension–elongation hysteresis, than to viscous damping. The snatch loads must be taken into account in the whole design process, which leads to an umbilical designed to resist to higher tension loads and implies also, in most cases, in over-dimensioned accessories, such as the bending limiters. Actually, due to the high level of friction between layers, the umbilical presents some level of structural damping which is, in fact, related to hysteretic moment-curvature and tension-elongation relations. This intrinsic structural damping may in fact contribute to the reduction of the snatch loads and considering it may reduce the level of conservatism in the design. However, due to the complexity and diversity of umbilical designs, it is not straightforward to come up with general-use hysteretic curves. A simplification then is to apply classic Rayleigh damping. Typically, damping levels of 5% are accepted in the offshore industry when using stiffness-proportional Rayleigh damping (the 5% damping is a percentage of the critical damping and is accounted for at the regular wave period or irregular wave spectral peak period). The problem here is that stiffness-proportional Rayleigh damping increases linearly with the frequency and the damping level at 1Hz, for example, may get to 60%. This fact indicates that the high-frequency part of the response may be simply discarded from the results, which in turn may lead to an incorrect, over-damped analysis. The present work aims tackling the Rayleigh damping issue, evaluating its effects on tension levels and spectral density of the tension time history. A recommendation of how to apply Rayleigh damping is proposed.
The Research of Moonpool Size Effect on the Hydrodynamic Performance of FDPSO
Authors: Wei Yuefeng , Yang Jianmin , Chen Gang , Hu Zhiqiang
Published: November 2011

FDPSO is a multifunction floating platform, which has the combined function of drilling, production, storage and offloading oil. The moonpool is necessary for drilling operation and the moonpool size effect will play a role on the hydrodynamic performance of FDPSO. A study of the moonpool size effect on such performance of FDPSO hull is presented in this paper, making use of numerical analysis and model tests techniques. The code WADAM is used for the hydrodynamic performance analysis. A model test aiming to validate the accuracy of the numerical analysis results was conducted in the Ocean Engineering basin in the State Key Laboratory of Ocean Engineering in the Shanghai Jiao Tong University. The model test included decaying test and white noise test. The decaying tests are performed in still water for heave, roll and pitch. White noise tests were carried out to obtain the RAO of FDPSO, with the wave incoming direction of 180° and 135°. The numerical results show a good agreement with the model test results, indicating a reliable model. The “piston” motion of the water inside the moonpool is significant, affecting the hydrodynamic performance of the FDPSO. The effect of moonpool size on the hydrodynamic performance of the FDPSO is analyzed through a numerical method. The relationship between the piston natural frequency of the water column inside the moonpool and its diameter and draft, are studied. An empirical formula of the “piston” natural frequency is proposed, and its validity is assessed.
Dynamic Simulation of Free-Spanning Pipeline Trawl Board Pull-Over
Authors: Longva Vegard , Sævik Svein , Levold Erik , Ilstad Ha˚var , Teigen Per
Published: November 2011

The main objective of this effort was to examine if finite element analyses can be used to predict pull-over loads from a trawl board. Here the trawl board was represented by a 6-DOF hydro-dynamic load model, where the mass and drag coefficients are expressed as functions of seabed gap, seabed inclination angle and heading angle. Both seabed proximity and forward-speed effects of the trawl board are hence included. The applied drag coefficients were established by model testing, while the hydro-dynamic mass was found by potential theory calculations. Compared to previous efforts, the hydrodynamic loading on the trawl board is represented in a far more consistent way in this paper. A simulation model which contained a polyvalent trawl board and a free-spanning pipeline was established. Several simulations were performed with span heights between 0 m and 2 m. In all simulations the pull-over force and pipeline response was sampled. The sampled results were thereafter validated by means of the analysis method and pull-over loading proposed in the DNV-RP-F111 code. Some differences could be observed in the response histories, but in summary the numerical model predicts a realistic pull-over. This indicates that the applied hydrodynamic load model captures the relevant effects during the pullover.
Wave Patterns, Wave Induced Forces and Moments for a Gravity Based Structure Predicted Using CFD
Authors: Thanyamanta Worakanok , Herrington Paul , Molyneux David
Published: November 2011

Gravity Based Structures (GBSs) are commonly used in the offshore oil and gas industry for storage during the production of hydrocarbons. The GBS sits on the sea bed, but it is subjected to forces and moments caused by waves. Obtaining accurate predictions of the magnitude of wave induced forces and bending moments is essential input to the structural design. Other key operational factors are the wave field in the vicinity of the structure and the amount of green water that will come onto the deck of the GBS. Scale model experiments can be used to obtain these predictions but this is an expensive option, especially in the early stages of a design, when many different concepts may be considered. An alternative method is to use Computational Fluid Dynamics (CFD). One CFD approach that is particularly suited to the challenges of predicting the required performance parameters for a GBS is the Volume of Fluid method, which is available in the commercial code Flow-3D. This paper presents the numerical simulation of the wave field around a surface piercing cylinder using the Volume of Fluid approach and compares it to published results. It also presents the simulations of the forces, moments and wave field around a proposed Gravity Based Structure, for which model data was available. The results show that predictions made using the Volume of Fluid method agree well with the observed wave patterns close to the structure in both cases, and that the method also gives good predictions of the observed forces and bending moments acting on the GBS.
Investigation Into Post-Ultimate Strength Behavior of Ship’s Hull Girder in Waves by Analytical Solution
Authors: Xu Weijun , Iijima Kazuhiro , Fujikubo Masahiko
Published: November 2011

To rationally assess the consequence of a ship’s hull girder collapse, it is necessary to know the post-ultimate strength behavior of the hull girder including the global deformation and motions under wave-induced extreme loads. In the foregoing research, the authors proposed a numerical analysis system to predict the collapse behavior in waves including the post-ultimate strength behavior. In this paper, an analytical solution to describe the post-ultimate strength behavior is proposed. The primary objective of the present research is to clarify the parametric dependencies of the severity of the collapse in a rational manner. The parameters may include those related to load-carrying capacity and those related to the extreme loads. By comparing the numerical results and the present results, the analytical solution is shown to be effective. Some important parameters to predict the severity of the collapse are derived based on the analytical solution.
Strength Analysis for a Spar in the Load-Out Operation Process
Authors: Yang Yue , Yang Jianmin , Hu Zhiqiang , Fan Zhixia , Sun Weiying
Published: November 2011

Load-out operation is one of the important processes for Spar construction and transportation. The Spar is towed onto the deck of a semi-barge, supported by special cradles during the whole process. Variation in weight distribution of the Spar, tidal changes, the barge draft level and positioning are main factors that affect the consistence of the barge deck and the dock surface, which will induce the Spar to sustain vertical bending moments and shear force. Transverse wind acting on the Spar also forms a slight transverse shift of the barge deck, which will induce the Spar to suffer horizontal bending moments. Nevertheless, structural components of the Spar are not allowed to endure any plastic deformations or buckling. So, the ultimate loading condition should be determined and the weakest structural components during the load-out process should also be ascertained. A truss Spar is chosen as the objective, and twenty steps are defined for the load-out process. The code SESAM is used to do the analysis. A finite element model is made, consists of the whole Spar and the cradle frames, which also take part in the load-out process. Two groups of load cases are defined. The initial forced displacement is applied on the cradle, simulating the difference between the deck and the dock surface. The initial forced displacement can be modified to the state when the Spar structural components endure ultimate elastic load. On the transverse wind condition, the initial forced displacement is modified in the same way introduced above. By the analysis results, two envelope curves for the vertical force applying on the barge are obtained, to provide guidance for the operation. The stresses and the internal forces of the Spar structural components are summarized, on purpose of giving the flexural performance and the shearing stress condition of the Spar during the load-out process. The ultimate elastic loads can be obtained for each of the twenty steps, and the characteristic of every ultimate elastic load cases is concluded. According to elastic-plastic theory, affordable displacement between barge deck and dock surface is obtained.
Materials Property Requirements for Mobile Offshore Installations
Authors: Pisarski H. G. , Stacey A.
Published: November 2011

Material properties requirements specified in codes, standards and classification society rules for mobile installations differ and a study was undertaken to identify current limitations and evaluation the effects on flaw tolerance. This paper summarises the results of the study and provides recommendations for maintaining a constant flaw tolerance as yield strength is increased.
A Novel Offshore Windmill Foundation for Heavy Ice Conditions
Authors: Eranti Esa , Lehtonen Eero , Pukkila Heikki , Rantala Lasse
Published: November 2011

A pilot offshore wind turbine with a new type of an ice-resistant foundation was installed in the Pori sea area of the Northern Baltic Sea during summer 2010. The water depth at the site is nine meters and the ice and wave conditions occasionally get quite heavy. The gravity-type foundation consists of a light ice-strengthened steel shell with a ring footing, ice-breaking cone, and crushed rock fill. The fill provides mass for the foundation and supports the shell against local ice impacts and moments caused by uneven base pressures, as well as stability for the thin shell structure. The ring footing extends the stabilizing moment arm and provides anchorage against overturning. This foundation concept is applicable to a variety of water depths with firm to hard bottom conditions. Foundation erection is fast and easy, making it well-suited for industrial wind farm roll-out.
An Experimental Study of the Effects That Change the Vibration Mode of Riser VIV
Authors: Fujiwara Tomo , Uto Shotaro , Kanada Shigeo
Published: November 2011

In recent years, a number of deepwater development projects are running worldwide. As the water depth increases, safety and reliability of the riser is a critical issue. One of the most important matters is vortex-induced vibration (VIV). In the deepwater area with strong current, for example in the Gulf of Mexico, a riser pipe’s VIV motion changes continually due to the change of hydrodynamic conditions. In order to assess safety and reliability of deepwater riser, investigation of the dynamic variation of riser VIV is important. This paper deals with top tensioned riser. To clarify the phenomena of dynamic variation of the riser’s vibration mode, a large-scale experiment using a 28.5 m long model was carried out at the Deep Sea Basin of the National Maritime Research Institute in Japan. In this experiment, the model’s bottom end was fixed, while top end was connected to a tensioner. The current generating system was installed to make flow from water surface to about 5m in depth. A measurement of riser VIV motion in current condition was carried out by changing the model’s top tension from self-weight balanced condition to four times of the self-weight. Vibration mode widely changed from high mode of up to 15th to low mode of 5th. In order to investigate an influence of the change of vibration mode on the riser VIV motion, a series of experiments were conducted with the periodic variation of top tension. It was found that the traveling wave occurred from top to bottom end in a moment of vibration mode changed.
Hydraulic Transport of Sand/Shell Mixtures
Authors: Ramsdell Robert C. , Miedema Sape A. , Talmon Arno M.
Published: November 2011

When considering pumping shells through a pipeline we have to consider that the shells are not spherical, but more discs shaped. When shells settle they will settle like leaves where the biggest cross section is exposed to the drag. But when they settle, they will settle in the same orientation, flat on the sediment, so the sides of the shells are exposed to the horizontal flow in the pipeline. Since the side cross section is much smaller than the horizontal cross section, a much higher velocity is required to make them erode and go back into suspension. The settling velocity is much smaller because of the large area of the cross section. Even when the slurry velocity exceeds the settling velocity, there will always be some shells that will reach the bottom of the pipe due to the combination of settling velocity and turbulence. Once these shells are on top of the sediment they are hard to remove by erosion, because they lay flat on the surface and have a small cross section that is exposed to the flow compared with the weight of the shell. So although their settling velocity is much lower than equivalent sand particles, the erosion velocity is much higher. If we look at the beach in an area with many shells, we can always see the shells on top of the sand, covering the sand. In fact the shells are shielding the sand from erosion, because they are hard to erode. The bigger shells will also shield the smaller pieces, because the smaller pieces settle faster. Compare this with leaves falling from a tree, the bigger leaves, although heavier, will fall slower, because they are exposed to higher drag. The same process will happen in the pipeline. Shells settle slower than sand grains, so they will be on top of the bed (if there is a bed), just like on the beach. Since they are hard to erode, in fact they protect the bed from being eroded, even if the line speed is increased. The combination of high erosion velocity and the shell ‘protecting’ the bed means that even a small amount of shells can lead to relatively thick bed in the pipeline. But there will always be velocities above the bed that will make the shells erode. The paper describes the settling and erosion process of shells and the consequences of this on the critical velocity when pumping a sand/shell mixture through a pipeline. A mathematical model of the processes involved will be presented.
Ultra Heavy Wall Linepipe X65: Double Joint Girth Weld Performances for Severe Applications
Authors: Di Vito Luigi , Mannucci Gianluca , Morana Roberto , Lucci Antonio , Tintori Federico , Crippa Stefano , Armengol Mariano , Mota Noe´ , Pelcastre Mauricio , Ruiz Eduardo , Quintanilla He´ctor , Darcis Philippe
Published: November 2011

Tenaris and Centro Sviluppo Materiali (CSM) launched 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 scale pipe models. The full project program aims at developing a new generation heavy wall product, supported by: comprehensive laboratory analysis of the material response under severe mechanical loading in aggressive environment; and full scale testing program, including both pipe and girth weld. Both investigations are mainly addressed to the basic understanding of impact on design criteria from interaction between severe loading and aggressive environment. Three papers have been already presented, in previous OMAE conferences, on this project. In the present paper, main outcomes of laboratory testing activities of the above program on girth welds for double jointing (fill passes by Submerged Arc Welding) are reported. A fitted for purpose special testing program, including mechanical and SSC laboratory scale testing, has been executed. Full thickness longitudinal specimens were extracted crossing girth weld to apply severe strain cycling. The strain cycling has been defined as extreme in terms of resistance against ratcheting for the pressurized pipeline, as deduced in a work reported in one of the previously mentioned papers. The girth welds exhibited very satisfactory performance during severe cyclic straining. Furthermore, mechanical and stress-corrosion properties of the As-Weld girth joint have been compared with the corresponding properties after severe straining and ageing. This comparison highlighted high level of mechanical and SSC resistance, even after the application of severe straining and ageing.
Global Performance of Synthetic Rope Mooring Systems: Frequency Domain Analysis
Authors: Falkenberg Erik , A˚hjem Vidar , Larsen Kjell , Lie Halvor , Kaasen Karl Erik
Published: November 2011

For deep and ultra-deepwater applications, synthetic fibre ropes are considered an enabling technology due to their higher strength-to-weight ratio as compared to steel wire ropes and chains and due to their superior station-keeping performance. The advantages of synthetic fibre rope mooring systems include: • A higher floater payload and reduction in structural costs due to lower vertical load from mooring lines. • A reduction in vessel offsets and associated riser loads due to taut mooring system. • A potential reduction in installation costs due to lighter installation and handling equipment. • Superior endurance under cyclic loading compared to steel moorings. Synthetic fibre ropes have visco-elastic stiffness and stretch characteristics. The change-in-length response of a fibre rope is non-linear, load-path dependent (different unload-reload stiffness), and the length varies with the rate and duration of loading (due to elongation and contraction). The commonly accepted analysis approach is a simplification where a lower-bound and an upper-bound stiffness is used. This practice is primarily based on two factors: 1. The industry at large does not at present have a common, well-defined understanding of fibre-rope change-in-length performance. 2. There is a lack of commercially available mooring analysis programs with the capability to simulate the non-linear change-in-length response of the synthetic fibre rope. Individual designers may however have more advanced analysis procedures, but these are not commonly accepted yet. This paper presents results from the Syrope pilot study, Ref. /5/ and /6/, which has used rope testing to determine the characteristics of the elements in the spring-dashpot model. On this basis a strategy for software implementation in the frequency-domain has been proposed. A case study was performed for a semi-submersible production unit in deep water and harsh environment. The paper focuses on the differences between a commonly accepted, hereafter called traditional analysis approach and the proposed new frequency domain approach. The results show that there are large differences in extreme tensions and offsets as well as fatigue results. Hence, the new approach is considered to represent a significant improvement.
Behavior of the Pontoon Supported by Mooring Dolphin in Tsunami
Authors: Masuda Mitsuhiro , Masuda Koichi , Ikoma Tomoki , Shouji Kuniaki
Published: November 2011

In recent years, the floating facilities for the ocean space utilization such as the marine disaster prevention base, the floating restaurant, floating type container terminals are planned and some of those facilities are actually built. Most of these facilities are the pontoon type floating structure, and the mooring system is a mooring dolphin. In the design of such facilities, it is important that the prediction of the behavior of the pontoon type floating body supported by mooring dolphin in tsunami the objective of present research is to develop the simulation system for the prediction of the behavior of the pontoon type floating body supported by mooring dolphin in tsunami. In present simulation system, the 3D-MPS method is applied, and the solitary wave and the bore like wave are applied as a assumed tsunami. The present paper is a report of the first stage of the research, and the heaving motion on floating body in the tsunami is paid to attention, and it reports on the result of examining the detaching from mooring dolphin of floating body.
Novel Design of Small Diameter Pipelines on Uneven Seabed
Authors: Hove Frode , So̸reide Tore H. , Nordsve Anne Cecilie , Trier Sigurd D.
Published: November 2011

The paper deals with design philosophy for small diameter HP/HT flowlines on uneven seabed with major emphasis on controlled snaking expansion design of free spanning flowlines subject to fishing gear interaction loads. The response from trawl pull-over is given major attention as part of the overall design procedure including ECA (Engineering Criticality Assessment), covering high and low cycle crack growth. The background for the design procedure is reference projects in the Norwegian sector, where REINERTSEN performed the flowlines detail engineering. Iceberg plough marks make an irregular seabed with partly sharp and deep valleys crossing the flowline routes, resulting in free spans. The bathymetry and extent of unevenness varies for the lines, resulting in different behavior and design approaches, especially for trawl pull-over. The major criterion for a robust design is strong sectioning by intermittent rock berms. For operation loads these serve as locking points and as such they are termed ARBs (Anchoring Rock Berms), whereas for trawl pull-over axial motion through the berms is allowed, depending on seabed profile, and as long as the pipeline deforms without unacceptable crack growth in girth welds. Design criteria for the ARBs are presented, covering the expansion phases of buckle initiation, post-buckle and shutdown, respectively. For trawl pull-over separate control of the intermittent rock dumps is shown, covering the cases of section interaction and complete locking, respectively. Criteria for the choice of trawl design approach are evaluated. Traditional design handles the trawl impact capacity of pipelines by a local buckling criterion, in which axial force and bending moment are the response parameters. For expansion control this is a relevant approach, however for a concentrated and curvature. Applying the latter criterion is illustrated by numerical example in view of displacement- or load controlled behaviour. A summary on rock saving potential is made for a typical reference project from a traditional design involving infill of spans to the new approach where free spans are allowed also for trawl pull-over. The potential cost saving for seabed intervention work by rock dumping is found to be well above 5000 NOK/m (>1000 $/m) for very irregular seabed, while typically in the order of 1000 $ for normal uneven seabed.
Direct Calculation of Fatigue Damage of Ship Structure Details
Authors: Li Zhiyuan , Ringsberg Jonas W.
Published: November 2011

Fatigue assessment of ships using the direct calculation approach has been investigated by numerous researchers. Normally, this approach is carried out as either a global model analysis, or as a local model structural analysis. The current investigation presents a case study of a container vessel where the global and local analyses procedures are combined. A nonlinear time-domain hydrodynamic analysis followed by a global FE analysis is employed to screen for the most severe locations of the global ship’s hull with regard to fatigue damage. Once these locations have been identified, a sub-modelling technique is employed to transfer global loads from the global FE model to local FE models that have high resolution of elements for local structure details. Results from a selection of local FE model simulations are presented. Stress concentration factors at four critical locations are calculated and compared with values recommended by classification guidelines. Results are presented from a short-term fatigue analysis which has been carried out using the rainflow counting method. Finally, a long-term fatigue analysis is performed in time-domain using a designed wave scatter diagram of representative sea states.
Comparison of Numerical Methods for Wave Generation by VOF-Based Numerical Wave Tank
Authors: Guo Bingjie , Steen Sverre
Published: November 2011

Based on the Reyonlds Averaged Navier-Stokes (RANS) equation for incompressible, viscous fluid, a VOF-based numerical wave tank which could accurately generate and absorb waves is investigated. Three different wave-making functions, namely ‘Inlet-velocity boundary condition (IBC)’, ‘Momentum source (MOS)’, ‘Mass source (MAS)’ are investigated, and the advantage of each method is analyzed to guide an optimal selection of these functions. Moreover, the effects of viscous model, grid size, time step, and discretization method on the accuracy of the wave simulation are discussed. The interaction between the wave and current is also studied. In order to verify the applicability of these methods, the numerical results in both 2D and 3D tanks are compared with analytical solutions.
Model Experiments on the Motion of a SPAR Type Floating Wind Turbine in Wind and Waves
Authors: Chujo Toshiki , Ishida Shigesuke , Minami Yoshimasa , Nimura Tadashi , Inoue Shunji
Published: November 2011

The study of floating offshore wind turbines has recently been attractive to many research groups in the renewable energy. Because the area of shallow water along Japanese coast is limited, the development of floating base for wind turbine is inevitable for making large scale wind farms. There are some problems to be solved for floating offshore wind turbines. Besides the mechanical problems of turbines, the influence of the motion of the floater in wind and waves to the electric generation properties, the safeties of floating structures such as the fatigue of machines and structures or criteria of electric facilities should be studied. Several types of floating structures have been proposed such as SPAR, TLP, pontoon, and semi submersibles. The authors have focused on SPAR type because its simpler shape seems to have economical advantages. In this paper, the authors performed experiments in a wind tunnel and a water basin from the viewpoint of “wind turbines on a SPAR type floating structure”. Firstly, forced pitching experiments were operated in a wind tunnel, and the difference in two types of wind turbines, upwind type and downwind type, is discussed. The former type is very popular and the latter type is thought to be suitable for floating structure. Secondly, experiments which thought to be more relevant for a floating wind turbine were carried out in a water basin. The relationship between the location of the attachment point of mooring lines and the motion of the SPAR in waves, and the influence of pitching angle of turbine blades to the motion of the SPAR in waves were inspected. In these experiments it was used a mechanism to control the pitch angle of the blades of the scale model of wind turbine.
A Methodology for Assessment of Internal Flow-Induced Vibration (FIV) in Subsea Piping Systems
Authors: Urthaler Yetzirah , Breaux Lyle E. , McNeill Scot I. , Luther Eric M. , Austin Julian , Tognarelli Michael
Published: November 2011

A methodology is presented for assessing internal flow-induced vibrations (FIV) in subsea piping systems. Finite Element (FE) models are constructed for the subject piping systems, including insulation, internal hydrocarbon weight and added mass of the surrounding sea water. Operating vibration data are measured using ROV-deployable accelerometer loggers clamped directly to the piping systems. The measured data are processed, analyzed and used for two purposes: model verification and dynamic response correlation. Modal parameters are extracted from the measured data and compared to the modal parameters computed from the structural FE model. The model is refined until the frequencies and mode shape errors are within the desired tolerance. The measured data are then used to derive a representative forcing function for use with frequency-domain random response analysis. The forcing function is derived such that the properties of the predicted vibration spectrum match those of the measured vibration spectrum for all measurement locations. The method presented herein provides a novel semi-empirical technique for calibrating FE models to make fatigue life predictions for subsea piping systems using measured vibration data.
Qualification of Reeled Clad SCR Weld Fatigue Performance
Authors: Wang Howard , Widener Troy , Kan Wan , Sutherland Jim , Jones Richard
Published: November 2011

Steel Catenary Risers (SCRs) are commonly used in deepwater field developments due to the cost benefits associated with their relatively simple geometry. Installation of SCRs by reel lay is generally the most cost effective approach. One of the major design challenges for SCRs is ensuring adequate fatigue performance at highly stressed regions. Since many deepwater projects require corrosion resistant alloy materials due to sour service requirements, an attractive option is to use metallurgically bonded clad pipes. However, there are very limited full scale fatigue test data available for clad SCR welds to confirm the technical viability of installing clad SCRs using the reel lay method. Thus, a study program was developed to qualify a suitable welding procedure for clad SCRs and to demonstrate that the required fatigue performance can be achieved using reel lay as the method for installation. This paper presents the testing results from the study program, which included full-scale qualification of clad X-65 pipe with alloy 625 welds having undergone reeling simulations. The results from this qualification program demonstrate that the selected welding procedure achieves high quality clad SCR welds with excellent fatigue performance in the reeled condition. This will enable projects using clad SCRs to consider reel lay as an acceptable method of installation. It will also extend the applicability of clad SCRs installed by the reel lay method to more severe environment conditions. This paper also discusses the impact on fatigue performance resulting from different reeling simulation approaches.
The Adequacy of Phase-Averaged Models for Modelling Wave Farms
Authors: Folley Matt , Whittaker Trevor
Published: November 2011

As the wave energy industry develops there is a need to develop tools for the estimation of the energy yield from wave farms, as well as determination of the environmental impact of wave farms and optimisation of wave farm layout. Tools based on spectral wave models are potentially suitable for these tasks and are already used extensively in coastal engineering to estimate wave climate and how waves affect the coastal environment. Examples of these tools include software packages such as SWAN, TOMAWAC and Mike21SW. However, a fundamental characteristic of spectral wave models is that they are phase-averaged models, which implies that the phase of individual wave components is unknown. Interactions between wave energy converters (WECs) in an array have been previously modelled using linear wave theory. These models have shown that phase can be important in determining the interaction between WECs in an array due to the effects of radiated waves. However, these models have typically assumed that the WECs have ideal control. The array interactions for more realistic control strategies are much weaker. In this paper arrays of realistically controlled WECs are modelled using hydrodynamic coefficients obtained from WAMIT, a linear hydrodynamic panel code, to determine the effects that radiated wave amplitude and WEC separation distance have on array interactions. It is shown that array interactions decrease with decreasing radiated wave amplitude and increasing separation distance. Array interactions are shown to change the power capture by less than 10% for typical WECs with realistic control. Moreover, it is shown that the change in power capture becomes highly sensitive to wave frequency and direction as the separation distance increases, although the magnitude of the interaction factor reduces. Finally, realistic wave spectra are applied to the array interactions of WECs. The average array interaction factor is found to be relatively insensitive to the mean wave period and direction. It is argued that this implies that phase-averaged models are adequate for modelling realistically controlled wave farms operating in realistic wave spectra. Consequently, provided a suitable phase-averaged model of a WEC can be developed, then it can be modelled with reasonable accuracy in spectral wave models.
Operational Margin From Weather and Motion Database for Heavy Transport Vessels
Authors: de Jonge Jan B. , Peters Onno A. J.
Published: November 2011

While shipping large and heavy cargo like jack-up rigs or semi-submersibles, the Motion Monitoring and Captain Decision Support system is a valuable tool to ensure a safe and economical voyage. Using the dynamic characteristics of the vessel, in combination with 5-day weather forecasts and design limits like maximum accelerations at the cargo location, roll motion and/or leg bending moments, more and better information is available to the Master to choose safe route, heading and speed. This way the best knowledge of what to expect is contributing to the safety of cargo, vessel and crew. The Octopus onboard system gathers a large amount of information about ship position, speed, heading, nowcast weather data and corresponding ship motion data. Reference is made to the paper of Peters [2] for background information of the Octopus Motion Monitoring and Decision Support system and an overview of methods used by the motion measurement system. In May 2008 the first Dockwise vessel started to gather weather and ship motion data. It is estimated that each vessel gathers around 50.000 nautical miles of data in a year, which is all collected in a database. The paper presents how this information is used for general research to environmental data, ship motion data and comparison to design values. Scatter diagrams from nowcast weather data can be produced. After collecting a certain amount of measurements, so called Dockwise scatter diagrams could be used as input for future voyage calculations. With this engineering approach Masters decisions for weather routing and bad weather avoidance is taken into account. This could lead for example to reduced design wave for a passage around the Cape of Good Hope. Now casted weather data and ship motions data is compared to design values from the cargo securing manual. Statistics like maximum difference, average difference give extensive data and insight in the operational margin of Dockwise transports. The calculation of the operational margin is independent of the standard safety margin valid for each transport. The conclusion is that the recorded nowcast significant wave height for the analyzed voyages never exceeded 5.0 [m]. With larger design wave heights the minimum operational margin increases to more than 40%, while the lowest operational margin occurs at design wave heights around 4.5 [m]. The database built by gathering all relevant information from the system and from crew observations, increases insight in the operational margins, which contributes to increased knowledge and safety.
Gap-Filling and Predicting Wave Parameters Using Support Vector Regression Method
Authors: Golestani Maziar , Zeinoddini Mostafa
Published: November 2011

Knowledge of relevant oceanographic parameters is of utmost importance in the rational design of coastal structures and ports. Therefore, an accurate prediction of wave parameters is especially important for safety and economic reasons. Recently, statistical learning methods, such as Support Vector Regression (SVR) have been successfully employed by researchers in problems such as lake water level predictions, and significant wave height prediction. The current study reports potential application of a SVR approach to predict the wave spectra and significant wave height. Also the capability of the model to fill data gaps was tested using different approaches. Concurrent wind and wave records (standard meteorological and spectral density data) from 4 stations in 2003, 2007, 2008 and 2009 were used both for the training the SVR system and its verification. The choice of these four locations facilitated the comparison of model performances in different geographical areas. The SVR model was then used to obtain predictions for the wave spectra and also time series of wave parameters (separately for each station) such as its Hs and Tp from spectra and wind records. New approach was used to predict wave spectra comparing to similar studies. Reasonably well correlation was found between the predicted and measured wave parameters. The SVR model was first trained and tested using various methods for selecting training data. Also different values for SVM parameters (e.g. tolerance of termination criterion, cost, and gamma in kernel function) were tested. The best possible results were obtained using a Unix shell script (in Linux) which automatically implements different values for different input parameters and finds the best regression by calculating statistical scores like correlation of coefficient, RMSE, bias and scatter index. Finally for a better understanding of the results, Quantile-Quantile plots were produced. The results show that SVR can be successfully used for prediction of Hs and wave spectrum out of a series of wind and spectral wave parameters inputs. Also it was noticed that SVR is an efficient tool to be used when data gaps are present in the data.
Prediction of Cross-Shore Beach Profile Evolution in the Vicinity of Seawalls
Authors: Lashteh-Neshaei Seyed Ahmad , Lotfollahi-Yaghin Mohammad Ali , Biklaryan Morteza
Published: November 2011

Although there exist advanced models which predict to beach profile for natural beaches, the behavior of the beaches in front of seawalls still suffers from the lack of appropriate theoretical models and sufficient measured data. Following the results obtained from the measurements, a beach profile evolution model is developed, using the measured probability distribution of the near-bed horizontal velocities as input, to predict the short-term bed level changes in the vicinity of e partially reflective seawall. The present model introduces a new approach in which based on integrating the probability density functions of the near-bed horizontal velocities, the sediment displacements and consequently bed level changes are calculated in front of a partially reflective structure. The results obtained from the model and comparison with the experiments are promising and encouraging for further developments of the proposed model.
Traveling Wave Response in Full-Scale Drilling Riser VIV Measurements
Authors: Marcollo Hayden , Eassom Adrian , Fontaine Emmanuel , Tognarelli Michael , Beynet Pierre , Constantinides Yiannis , Oakley Owen H.
Published: November 2011

The dominance of traveling wave VIV response is observed in full-scale measured drilling riser data for the first time. This paper presents the novel methods developed to identify the presence of traveling versus standing wave riser structural response in the full-scale data and the observations. This paper reports on some of the work conducted under the most recently completed phase of the DeepStar JIP (Phase 9). The paper uses four different novel methods to identify the presence of traveling versus standing wave structural response in data obtained from a full-scale Gulf of Mexico drilling riser during a loop current event. The techniques are: 1) Observation of RMS accelerations between synchronized accelerometers; 2) Observation of filtered displacements between synchronized accelerometers (using a new postprocessing synchronization technique); 3) Displacement versus angular rate phase diagrams; and 4) Derivation of upward/downward curvature components via an algorithm proposed by two of the co-authors. High level conclusions are drawn about the structural response types. Recommendations for future instrumentation campaigns are made.
Advanced Analysis and Design Tools for Offshore Pipeline in Operation
Authors: Bartolini Lorenzo , Crea Cristian , Marchionni Lorenzo , Spinazze` Maurizio , Vitali Luigino
Published: November 2011

In the last thirty years, the attention of the offshore pipeline industry has been strongly focused on submarine pipelines crossing very uneven seabed. New pipelines crossing the uneven seabed of the Mediterranean Sea and of the North Sea and deep water pipelines crossing the uneven continental slope of the Gulf of Mexico are outstanding examples. Pipeline structural integrity may be threaten by large free-spanning sections between rocky peaks and deep depressions that may be coupled with the pipeline propensity to develop lateral/vertical deflection due to severe service conditions (High Pressure/High Temperature). Generally, these scenarios require mitigation measures aiming to control the development of excessive bending moment/deformation by means of Finite Element (FE) Modeling. FE Modeling gives a valuable contribution to the pipeline engineering at identifying a technical and cost effective solution since the early phase of the project. Finite Element (FE) Model approaches, based on standard structural finite element codes available on the market, such as ABAQUS, ADINA, ANSYS etc., are commonly used to analyze the effects of non-linearity, e.g. steel material, soil-pipe interaction and large rotations/displacements. 3-Dimensional FE Models permit to predict the overall pipeline global response under design loads taking into account the expected (during design phase) and/or actual (after measurements gathered during as-built survey campaign) 3-Dimensional pipeline configuration including 3-Dimensional (along and transversal to the pipeline route) bottom roughness, route bends, intervention works for bottom roughness and free-span correction and mitigation measures against HP/HT condition in operation. In this paper: • The design approach for HP/HT pipelines is described; • The main features of the ABAQUS FE Model, developed to predict the behavior of offshore pipelines in operation, are presented; • Two relevant examples of offshore pipelines subject to pressure and temperature conditions are presented with and without mitigation measures.
New Insights in Extreme Crest Height Distributions: A Summary of the ‘CresT’ JIP
Authors: Buchner Bas , Forristall George , Ewans Kevin , Christou Marios , Hennig Janou
Published: November 2011

The objective of the CresT JIP was ‘to develop models for realistic extreme waves and a design methodology for the loading and response of floating platforms’. Within this objective the central question was: ‘What is the highest (most critical) wave crest that will be encountered by my platform in its lifetime?’ Based on the presented results for long and short-crested numerical, field and basin results in the paper, it can be concluded that the statistics of long-crested waves are different than those of short-crested waves. But also short-crested waves show a trend to reach crest heights above second order. This is in line with visual observations of the physics involved: crests are sharper than predicted by second order, waves are asymmetric (fronts are steeper) and waves are breaking. Although the development of extreme waves within short-crested sea states still needs further investigation (including the counteracting effect of breaking), at the end of the CresT project the following procedure for taking into account extreme waves in platform design is recommended: 1. For the wave height distribution, use the Forristall distribution (Forristall, 1978). 2. For the crest height distribution, use 2nd order distribution as basis. 3. Both the basin and field measurements show crest heights higher than predicted by second order theory for steeper sea states. It is therefore recommended to apply a correction to the second order distribution based on the basin results. 4. Account for the sampling variability at the tail of the distribution (and resulting remaining possibility of higher crests than given by the corrected second order distribution) in the reliability analysis. 5. Consider the fact that the maximum crest height under a complete platform deck can be considerably higher than the maximum crest at a single point.