bluuebunny/crossref_metadata_2025 huggingface dataset:
Validation of a Computer Model for Flexible Pipe Crushing Resistance Calculations
Authors: Malcorps Aline , Felix-Henry Antoine
Published: July 2009

Several types of laying equipments are used to install flexible pipelines for offshore field developments. These pipelines installation tools apply generally compressive radial forces to hold the pipe suspended weight. The deeper the pipeline has to be laid, the higher is its suspended weight and therefore the higher these radial loads need to be. As each flexible pipe construction is optimized for each field application, a design methodology is necessary to be able to evaluate the radial load acceptable by the flexible pipe. The failure mode associated with this type of loads is an instability thought to be similar to the hydrostatic collapse mode. Therefore an adequate design safety factor has to be considered. The water depth of offshore field developments becoming ever deeper, the resistance of the flexible pipe to installation loads becomes often a driving design criterion. A finite element model to address this type of loading has been developed and improved over the past years. To avoid over-sizing the flexible pipe with current design approach, this finite element model needed to be improved for the latest materials used and for higher crushing loads. To this effect, a new powerful test bench with a crushing load capacity of 1200 tons over one meter has been designed, procured and is now operational. It can handle pipes from 4" to 19" internal diameter. Many types of flexible pipe samples have been tested up to permanent deformation using bi-, tri- and quadri-caterpillar tensioners. The results of these tests have been used to validate a new finite element model using in particular non-linear elasto-plastic material laws. In this paper, several test results will be presented and compared with the calculations. The relevance of different possible design criteria depending on the type of loading regime, the slenderness of the pipe and the number of radially resistant layers, will also be discussed. This new model is operational and allows to optimize the flexible pipe design in particular for ultra-deep water applications down to 2500m or more.
In-Situ Vibration Monitoring of Pipeline Freespans
Authors: Job Paul , Hawkins Mike
Published: July 2009

A wide network of subsea pipelines are in operation in the Gulf of Thailand. Due to the undulating nature of the seabed, many of these pipelines have freespans, which may be both long and high. In the past, some remedial works have been carried out to provide support to these spans to control flow induced vortex induced vibrations (VIV). However, due to the large quantity of pipeline freespans and the soft sediment of the seabed in the region, it became necessary to develop a rigorous method for prioritizing remedial works. In response to the specific difficulties encountered in this area, the operator implemented a programme of monitoring the vibrations on those spans identified as most susceptible to VIV. New equipment developed for this programme incorporated sensors for the measurement of both pipeline movement and local water velocity and a data logger to record these data. The features and development of the span monitoring equipment are described, the issues of data analysis and interpretation are discussed, and measured responses are compared with predicted.
Efficient Solution of the 3D Laplace Problem for Nonlinear Wave-Structure Interaction
Authors: Bingham Harry B. , Engsig-Karup Allan P.
Published: July 2009

This contribution presents our recent progress on developing an efficient solution for fully nonlinear wave-structure interaction. The approach is to solve directly the three-dimensional (3D) potential flow problem. The time evolution of the wave field is captured by integrating the free-surface boundary conditions using a fourth-order Runge-Kutta scheme. A coordinate-transformation is employed to obtain a time-constant spatial computational domain which is discretized using arbitrary-order finite difference schemes on a grid with one stretching in each coordinate direction. The resultant linear system of equations is solved by the GMRES iterative method, preconditioned using a multigrid solution to the linearized, lowest-order version of the matrix. The computational effort and required memory use are shown to scale linearly with increasing problem size (total number of grid points). Preliminary examples of nonlinear wave interaction with variable bottom bathymetry and simple bottom mounted structures are given.
A Study on Predictions of Fully Nonlinear Motion Aircushion Type Floating Structures Using 2D MPS Method
Authors: Masuda Mitsuhiro , Ikoma Tomoki , Masuda Koichi , Maeda Hisaaki
Published: July 2009

Very large floating structures (VLFSs) have been proposed for new ocean space utilization and many researches have been carried out. VLFSs are elastically deformed due to ocean waves because the rigidity of the structure decreases relatively. The authors examine the aircushion type floating structure in order to reduce hydroelastic motion. An aircushion type floating structure to which air-chambers are installed can reduce the wave drifting force and hydroelastic motion at the same time. Most theoretical calculations of motion of aircushion type floating structures in water waves have been done based on a linear potential theory so far. As a result, the utility of the aircushion has been proved. However fully nonlinear phenomena such as deck wetness, slamming and air-leakage cannot be investigated by using existing calculations based on the linear theory. In this study, a computer program code of the two-dimensional MPS method that can consider fully nonlinear influence is developed and then the air layer inside an aircushion is expressed with particles of the MPS. Moreover, the numerical technique for introducing directly the mooring force into the motion equation of the particle is developed. Motion response of aircushion type floating structures in a billow is computed. As a result, the usefulness of this numerical calculation method is confirmed.
A Non-Linear Numerical Method for the Simulation of Parametric Roll Resonance in Regular Waves
Authors: Ahmed T. M. , Ballard E. J. , Hudson D. A. , Temarel P.
Published: July 2009

In this paper, a non-linear time-domain method is used for the prediction of parametric roll resonance in regular waves, assuming the ship to be a system with three degrees of freedom in heave, pitch and roll. Coupled heave and pitch motions are obtained using a three-dimensional frequency-domain potential flow method which also provides the requisite hydrodynamic data of the ship in roll i.e. the potential flow based added inertia and damping. Periodic changes in the underwater hull geometry due to heave, pitch and the wave profile are calculated as a function of the instantaneous breadth. This is carried out using a two-dimensional approach i.e. for sections along the ship and at each time step. This formulation leads to a mathematical model that represents the roll equation of motion with third order non-linearities in the parametric excitation terms. Non-linearities in the roll damping and restoring terms are also accounted for. This method has been applied to two different hull forms, a post-Panamax C11 class containership and a transom stern Trawler, both travelling in regular waves. Special attention is focused on the influence of different operational aspects on parametric roll. Obtained results demonstrate that this numerical method succeeds in producing results similar to those available in the literature, both numerical and experimental.
Ultra-Deepwater Model Testing of a Semisubmersible and Hybrid Verification
Authors: Kendon Timothy E. , Oritsland Ola , Baarholm Rolf J. , Karlsen Svein I. , Stansberg Carl-Trygve , Rossi Ronaldo R. , Barreira Rodrigo A. , Matos Vinicius L. F. , Sales Joel S.
Published: July 2009

Model test verification of floater systems in ultra-deep water meets limitations when it comes to available laboratory sizes. Systems in depths beyond 1000–1500 m cannot be tested at reasonable scales without the truncation of the mooring and riser system. The development of methods and procedures to overcome this problem has been addressed through extensive research programs at MARINTEK (VERIDEEP, VERIDEEP Extension, NDP, DEMO2000). This led to a hybrid verification procedure which combines reasonable truncation principles, model tests of the truncated system, and numerical simulations, to estimate the system’s response at full depth. There is, however, still a need to address the actual influence from the truncation procedure, and from the integration with simulations, on the final extrapolated full depth results. This paper presents a case study for the validation of the procedure, that compares full depth model test results of a semisubmersible in water depth 1250m against the extrapolated full depth results obtained from a truncated system of 500m. Results are presented for line tension and vessel responses in 3 seastates. In general the extrapolated full depth results were found to be in good agreement with the full depth model tests. However, the results confirmed expectation that the low frequency response has the greater uncertainties and presents the greatest challenge for the procedure.
Parametric Roll: Highly Controlled Experiments for an Innovative Ship Design
Authors: Olivieri A. , Francescutto A. , Campana E. F. , Stern F.
Published: July 2009

The present work is focused on ship’s parametric roll. In particular, a series of controlled experiments have been performed in order to obtain repeatable results both for the inception and the roll amplitude in parametric roll condition. The experiments have been performed for an innovative ship design (a tumblehome shape) in a towing tank provided by a flap-type wave maker. The model was tested in 3 DoF conditions, being roll, pitch and heave motions free and surge, sway and yaw restrained. The experimental work, which is the subject of the present paper, is part of cooperative research project between the IIHR (Iowa Institute of Hydraulic Research), the University of Trieste and the Italian ship model basin (INSEAN) (1, 2). All the experiments have been carried out in head waves at the INSEAN basin n. 2. The model motions were measured both by an optical motion tracker (Krypton) and a gyroscopic platform (MOTAN). Tests were carried out for three different metacentric heights in a range of speeds. Roll decay tests as a function of forward speed were performed before every experiment in waves in order to determine the natural roll frequency and the roll decay rate. The head waves experiments showed parametric roll excitation for different metacentric heights, wave steepness and Froude number. The repeatability of the obtained results, allows to use them as a benchmark for both CFD codes and theoretical models. This will be the subject of a future work, which is at present in preparation and involves other international collaborations beyond the ones listed here.
Initiative on Structural Integrity Management of Ageing North Sea Installations
Authors: Stacey A. , Birkinshaw M.
Published: July 2009

With an ever-increasing population of ageing offshore installations in the North Sea, the Health and Safety Executive’s (HSE’s) Offshore Safety Division has focused its front-line operational activity in recent years on the structural integrity management process and establishing the extent of any deterioration in structural integrity. The current phase of work, the Structural Integrity Management Inspection Programme (SIMIP), is described and the findings to date are presented in this paper.
Pipeline-Laybarge Interaction Model for the Simulation of S-Lay Installation Procedures
Authors: da Silva Danilo Machado Lawinscky , de Lima Mauro Henrique A. , Jacob Breno Pinheiro
Published: July 2009

The most common method of pipeline installation in shallow water is the S-Lay method. In this method, the welded pipeline is supported by rollers on the vessel and the stinger, forming the over-bend. Then it is suspended in the water all the way to seabed, forming the sag-bend. The over-bend and sag-bend form the shape of an “S”. This work focus in modeling the interaction between pipeline and lay barge on the over-bend region, considering not only the contact between the pipeline and the launching structure, but also the tensioner behavior. Two numerical models are proposed: (a) a rigorous contact model that provides important information related to the consequences of impact between pipeline and rollers. These consequences can be dents to the pipe or tearing of the coatings; and (b) a model for the simulation of the tensioner behavior. This latter includes a delay between the instant that the tensioner is activated until it effectively starts working. It also considers how fast the tensioner can recover the desired tension level in the pipeline. Several simulations of actual operations are shown, in order to illustrate the application of the proposed model.
An Analytical Approach for the Calculation of Random Wave Forces on Submerged Tunnels
Authors: Romolo Alessandra , Malara Giovanni , Barbaro Giuseppe , Arena Felice
Published: July 2009

This paper deals with the random forces produced by high ocean waves on submerged horizontal circular cylinders. Arena [1] obtained the analytical solution of the random wave field for two dimensional waves by extending the classical Ogilvie solution [2,3] to the case of random waves. In this paper, the wave force acting on the cylinder is investigated and the Froude Krylov force [4], on the ideal water cylinder, is calculated from the random incident wave field. Both forces represent a Gaussian random process of time. The diffraction coefficient of the wave force is obtained as quotient between the standard deviations of the force on the solid cylinder and of the Froude Krylov force. It is found that the diffraction coefficient of the horizontal force Cdo is equal to the Cdv of the vertical force. Finally, it is shown that, given that a very large wave force occurs on the cylinder, it may be calculated, in time domain, starting from the Froude Krylov force. It is then shown that this result is due to the fact that the frequency spectrum of the force acting on the cylinder is nearly identical to that of the Froude-Krylov force.
Probabilistic S-N Fatigue Assessment Methods for Welded Joints in Offshore Structures
Authors: Muhammed A. , Stacey A.
Published: July 2009

A study of probabilistic fatigue assessment methods for offshore structures confirmed that fatigue life predictions for offshore welded joints is dominated by uncertainties in hot spot stress estimation, arising from uncertainties in nominal stress and stress concentration factors. Analysis of data from previous fatigue studies on North Sea jacket structures conducted in the late 1980s suggests that nominal stresses are, in general, overestimated by about 30% and the COV of the bias is about 0.35. The study demonstrated that in-service fatigue failure probability is not only dependent on the COV but also on the median bias of the nominal stress range. A number of nominal stress COVs are recommended with associated median values for general offshore application. Distributions are also suggested for other variables such as Miner’s damage sum and the S-N design curve coefficients. Methods based on long-term stress range distribution with random parameters to cater for uncertainties in stress estimation are described and example calculations are given.
A Case Study on the Axial-Torsional Behavior of Flexible Risers
Authors: Ramos Roberto , de Arruda Martins Clo´vis , Pesce Celso Pupo , Roveri Francisco E.
Published: July 2009

Flexible risers are complex structures composed of several concentric polymeric and steel armor layers which withstand static and dynamic loads applied by the floating production vessel and by the ocean environment. Determining the axial and torsional stiffness values of such structures is an important task for the global structural analysis, since it provides a probable value that can be used in this analysis to predict the load distribution along the line and permitting, thus, to estimate the expected life of the structure. Although such stiffness values may be provided by the manufacturer, it is quite desirable that they can be estimated by analytical models instead. However, any analytical model proposed for such a task must be checked with well-conducted experimental results in order to be considered as an acceptable analysis tool. The aim of this work is to present the main results involving axial-torsional tests in a 2.5" flexible riser, carried out at the Technological Research Institute of Sa˜o Paulo (IPT). Besides presenting full data concerning the internal structure of the riser, this paper describes the experimental procedures used to perform the tests and the main obtained results (e.g., Force × Displacement and Twisting moment × Displacement curves). Tests involving internal pressure were also performed and the obtained results are also presented in this work. Comparisons between analytically calculated values of the axial and torsional stiffnesses with those obtained experimentally are made and discussed. A brief discussion about the validity of some hypotheses which are usually assumed by analytical models found in the technical literature is made at the end of the work.
The Importance of Mode Number on In-Line Amplitude of Vortex-Induced Vibration of Flexible Cylinders
Authors: Swithenbank Susan B. , Larsen Carl Martin
Published: July 2009

Most empirical codes for prediction of vortex-induced vibrations (VIV) has so far been limited to cross-flow response. The reason for this is that cross-flow amplitudes are normally larger that in-line amplitudes. Additionally the in-line response is considered to be driven by the cross-flow vibrations. However since the in-line frequency is twice the cross-flow frequency, fatigue damage from in-line vibrations may become as important and even exceed the damage from cross-flow vibrations. A way to predict in-line vibrations is to apply traditional methods that are used for cross-flow VIV and establish an empirical relationship between the cross-flow and in-line response. Previous work suggests that the ratio between the in-line and cross-flow amplitudes depends on the cross-flow mode number, Baarhom et al. (2004), but the empirical basis for this hypothesis is not strong. The motivation for the present work has been to verify or modify this hypothesis by extensive analysis of observed response. The present analysis uses complex data from experiments with wide variations in the physical parameters of the system, including length-to-diameter ratios from 82 to 4236, tension dominated natural frequencies and bending stiffness dominated natural frequencies, sub-critical and critical Reynolds numbers, different damping coefficients, uniform and sheared flows, standing wave and traveling wave vibrations, mode numbers from 1–25th, and different mass ratios. The conclusion from this work is that the cross-flow mode number is not the important parameter, but whether the frequency of vibration in the cross-flow direction is dominated by bending stiffness of tension.
The Interaction of Nonlinear Waves With the Submerged Caissons of a Gravity Based Structure
Authors: Christou Marios , Roos Jannicke S. , Swan Chris , Gudmestad Ove T.
Published: July 2009

This paper concerns the numerical description of nonlinear waves propagating over the storage caissons of a gravity based structure. This process produces a steepening of the incident wave-field, which occurs when the waves propagate into the shallower water region above the storage caissons, resulting in the focussing of wave energy. A fully nonlinear Multiple-flux Boundary Element Method (MF-BEM) is applied to simulate this effect. The MF-BEM differs from traditional boundary integral approaches in two important respects: first, a multiple-flux approach is employed to overcome the problem of geometric discontinuities; and, second, no filtering, smoothing, re-gridding or redistribution of the nodes is performed at any stage during the simulations. These two aspects are believed to play an important role in accurately predicting the steepening of the incident wave-field. The numerical predictions are compared to new laboratory observations that examine the extent of this wave-structure interaction and, particularly, the steepening of the incident wave-field.
Effect of Reeling on Small Umbilical Tubing Fatigue
Authors: Buitrago Jaime , Doynov Krassimir , Fox Allen
Published: July 2009

Umbilicals use steel tubing of different sizes to carry various pressurized fluids. During manufacturing, transportation and installation of the umbilicals, the tubing is subjected to reeling and unreeling operations, resulting in a cumulative amount of plastic strain. The amount of strain varies with different cross-section designs and umbilical manufacturers. This plastic strain may limit the fatigue performance of the tubing in dynamic umbilicals, thereby limiting the number of reeling operations of umbilicals in deepwater. A previous paper presented a novel experimental methodology to simulate reeling and its effect on the fatigue of 57.6-mm ID × 3.4-mm WT made of super duplex steel. Results indicated that reeling can significantly degrade the fatigue performance of the welded tubing as the cumulative reeling strain increases up to 20%. This paper discusses an experimental program aimed at assessing the size effect on fatigue of reeled tubing. Ten 10 additional fatigue tests were conducted with 12.6-mm ID × 1.46-mm WT tubing reeled to 20% strain. Results indicate that the smaller tubing, once reeled to 20%, its fatigue performance degrades to the same level as that of the larger tubing. However, the combined fatigue data do not support current design criteria DnV-RP-C203. Therefore, given the uncertainty of all of the variables involved, fatigue qualification for specific applications is considered necessary.
A New Approach for Identification of Forces on Slender Beams Subjected to Vortex Induced Vibrations
Authors: Wu Jie , Larsen Carl M. , Kaasen Karl E.
Published: July 2009

Vortex induced vibration (VIV) has been subjected to extensive research during the last 20 years. A large number of laboratory and ocean tests with long slender beams or cables have been reported. Key results from such experiments have been response frequencies and amplitudes, but also information on mode composition and traveling waves. Due to the difficulty of direct force measurement, accelerometer and bending strain measurement are used in such experiments. Formally, it should be possible to identify the forces that have created the measured response, but so far few results from such attempts have been reported. An inverse force estimation method is adopted to provide an accurate way of reconstructing the unknown hydrodynamic forces from measured dynamic response data. The method is based on state space formulation of a finite element beam model. It incorporates the Kalman filtering and recursive least squares algorithm to remove the noise from measurement and obtain force estimation in discrete time domain. The inverse force estimation method is verified with numerical simulations. The input force of a tensioned beam structure is estimated from response. The result indicates its capability to accurately estimate the input forces from stochastic response. The method is applied to the data from Rotating Rig Test to identify hydrodynamic forces along the riser. The lift force and added mass coefficients are calculated and compared with existing data.
Numerical Simulations of Flow Past an Aspirated Fairing With Three Degree-of-Freedom Motion
Authors: Pontaza Juan P. , Menon Raghu G.
Published: July 2009

We simulate the flow past circular cylinders that are outfitted with plain and aspirated short aspect ratio fairings. Aspirated fairings aim to reduce the mean drag by means of suction holes and blow holes strategically placed around the circumference of the fairing. Several designs are presented here, including centered and off-centered suction, and the designs assessed in terms of mean drag reduction and vortex-induced vibration suppression. We consider flow conditions that correspond to a high Reynolds number of 106, and allow for three degree-of-freedom motions where the structure is allowed to respond to flow-induced cross flow forces, in-line forces, and spanwise moments. The computations are performed using a parallelized Navier-Stokes in-house developed solver using overset grids.
X80 UOE Pipe With Excellent HAZ Toughness
Authors: Terada Yoshio , Morimoto Hiroshi , Doi Naoki , Murata Masahiko
Published: July 2009

New X80 UOE pipe manufacturing technology has been developed to attain excellent CTOD properties in HAZ. In the new steel pipe, the HAZ microstructure near the weld fusion line is refined by utilizing the strong suppression of austenite grain growth as well as the formation of intragranular ferrite (IGF). The IGF grows radially from oxides in the same way as in Ti-O steel. The suppression of austenite grain growth is due to the pinning effect by fine particles including ultra fine oxides. As these oxides dispersed in the steels are chemically stable even near the fusion line, the microstructure can be refined. In addition, it is also necessary to suppress the formation of coarse grain boundary ferrite (GBF) near the weld fusion line in order to obtain excellent CTOD properties. So, it was found that the increase of boron addition in weld metal is effective to suppress the formation of coarse GBF near the weld fusion line because boron atoms diffuse into prior austenite grain boundaries near the fusion line from the molten pool during welding. This paper describes new technology for improving CTOD properties in HAZ. The X80 UOE pipe manufactured on a large scale and exhibited excellent CTOD properties at −30°.
Effect of Marine Growth on an Elastically Mounted Circular Cylinder
Authors: Skaugset Kjetil , Baarholm Rolf
Published: July 2009

The Riser and Mooring project of the Norwegian Deepwater Programme (NDP) has undertaken a parametric study on the influence of marine growth on the effectiveness of helical strakes to suppress vortex-induced vibrations on circular cylinders. Helical strakes are one of the most commonly used devices to suppress vortex-induced vibrations (VIV) on marine risers. The aim is provide guidance on the effect marine growth has on the dynamic response of a riser fitted with such VIV suppression devices. The tests were conducted at MARINTEK in a controlled laboratory environment. Artificial marine growth was modelled, manufactured and tested. Both hard and soft marine growth of various heights and coverages were tested. The present paper discusses some results obtained in this test campaign.
Fatigue Resistant Threaded and Coupled Connectors for Deepwater Riser Systems: Design and Performance Evaluation by Analysis and Full Scale Tests
Authors: Sches Celine , Desdoit Emmanuel , Massaglia Jacky
Published: July 2009

Threaded and Coupled (T&C) riser connectors with High Strength Steels have been developed for deepwater top tensioned riser (TTR) applications up to 10,000ft Water Depth. These developments have been ongoing for a decade, and the resulting solutions are now becoming the standard in the industry. Due to the stringent fatigue requirements involved, new design and performance evaluation methods were needed and have been built over time. In this article, we will demonstrate how these methods were implemented into the standard development process of T&C connectors, with a focus on finite element analysis (FEA) techniques. This process includes full scale tests programs on resonant fatigue frames, statistical post treatment of the resulting data, and fatigue cracks expertise for failure mechanism analysis. These elements are a key for the evaluation of T&C connectors’ fatigue performance and for the determination of influencing parameters, leading to the proper design optimization possibilities. The application of these methods will be illustrated with actual examples on T&C connectors’ recent developments. Namely, we will describe FEA methodologies, testing methods and results post-treatment techniques. We will show how the connectors’ performance is eventually derived after such analysis and test data accumulation. The reader will see that innovative and effective fatigue enhancement techniques have resulted, along with premium fatigue compliant sealing devices. The experience and expertise gained, together with a continuous improvement process of our methods have made T&C riser connectors a viable solution to meet emerging needs within deepwater industry, including xHP-HT, SCR and flow lines.
Current Effects on a Moored Floating Platform in a Sea State
Authors: Stansberg Carl Trygve
Published: July 2009

The significance of current-induced forces and effects on a moored semisubmersible production platform in various sea state conditions is explored, with emphasis on surge motions. Experimental data from 1:55 scaled model tests in a 50m × 80m wave basin are investigated. A description of the current generation is given first. The current in the actual basin is modelled by use of a return current under a false bottom. The importance of modelling a “real” physical current for the proper reproduction of platform responses is pointed out. The semisubmersible tests are carried out with the platform in current only, in irregular waves only, and in combined waves and current conditions. The effects from the current on platform motions and mooring line tensions are investigated. Vortex-Induced motions (VIM) are observed in pure current, depending on the actual combination of current velocity and natural sway period. In combined waves and current the VIM seems to be more or less disappearing. A large effect is seen on the wave drift responses. Both drift forces, non-Gaussian properties and resulting extreme motions and line tensions are significantly increased, especially in high sea states. This is explained through a combination of wave drift damping and viscous effects. At the same time the damping is also increased, but this only partly compensates for the increased forces.
Reduced Model Device of Solutions to Control Thermal Buckling Effects in HP-HT Subsea Pipelines
Authors: Silva-Junior Helio C. , Cardoso Carlos O. , Carmignotto Marco A. P. , Zanutto Jose C.
Published: July 2009

Nowadays, the safe operation of HP-HT subsea pipelines resting on seabed must take into account the thermal buckling phenomenon. The transport of oil with high pressure and temperature can cause uncontrolled thermal buckling in subsea pipelines. The failure risk must be carefully evaluated to design the pipeline with safety. Nowadays to control the thermal buckling the use of man made triggers is seen like the best solution for cost and safety of subsea pipelines. Some projects employ man-made triggers to control the thermal buckling in the last years around the world. In this article is presented the system and methodology used to test some solutions in a reduced scale model. Different geometric setups along the model line were tested. Solutions like sleepers, dual sleepers and buoyancy were tested and the geometric and structural behavior monitored. The reduced model has 195 m length, and was developed in the IPT Towing Tank, representing a pipeline section of almost 6 km long. Strains, temperature, pressure and displacements were measured in several sections of the model. Additionally, an imaging technique for the model geometry retrieval was developed. This paper presents the experimental setup developed to investigate the performance of man-made triggers solutions for HP-HT subsea pipelines.
Wave Design in Distorted Physical Model for Estuarine and Coastal Regions
Authors: Kong Lingshuang , Wang Na , Cao Zude
Published: July 2009

Wave design in distorted model for estuary and coast has been analyzed and equivalent wave was designed according to bottom shear stress. And at the same time the wave direction generated by wave generation is adjusted to reach refraction similarity.
Characteristics of the Infragravity Wave Climate
Authors: Masterton Stephen , Ewans Kevin
Published: July 2009

Infragravity waves are very long period waves below the frequency of typical wind waves. They are most significant in shallow water locations and therefore have a high impact on the response of moored vessels. For the Oil and Gas business this can be an important consideration for tanker on/offloading operations (including LNG vessels) — these larger vessels, with longer natural periods, are particularly susceptible. There are implications for both the design and operation including the calculation of extreme loading on the mooring system, extreme vessel motions, fatigue of mooring systems and the availability of on/offloading operations. There are currently limited design practices to account for the effect of infragravity waves. This may be attributed to two main factors: The development of infragravity waves is difficult to model and is sensitive to many factors, including the magnitude and shape of the incident wind and swell spectra, local bathymetry, directionality and near shore wave breaking. Secondly, very little measured data exist since the infragravity wave frequencies lie below the conventional range of commonly deployed wave measurement devices. The present paper will provide a description of the infragravity waves acting on the US coast at two locations, Duck, North Carolina, and Baja, California. The results will characterize parameters including the significant wave height, peak period, and comparison of infragravity waves through time. In addition, the relationships between the spectral shape will be examined including directionality. This type of information is needed to set design criteria for infragravity waves, and in the longer term to develop and enhance infragravity wave models e.g. Reniers 2002 (1) and ultimately contribute to establishing design practices.
New Data on the Capacity of X-Joints Under Tension and Implications for Codes
Authors: Dier Adrian F. , Smedley Philip , Solland Gunnar , Bang Hege
Published: July 2009

This paper reviews available static strength data and presents results of finite element analyses on first crack loads and ultimate loads of X-joints in tension. A critique of existing guidance for such joints is given. An examination of hot spot stress for such joints is presented, together with new capacity formulations based on test data. The new formulations are verified with reference to new data from a finite element analysis. The new capacity formulations will be of interest to regulatory authorities, to designers of new offshore installations and to engineers carrying out assessments of existing structures. It is also expected that the formulations will be considered by code drafting committees, e.g. for API RP2A, ISO 19902 and NORSOK, during code revisions. The paper demonstrates that present guidance is unduly conservative in two respects: (1) high γ joints (i.e. thin-walled chords) in the range 0.7 ≤ β ≤ 0.9 joints (i.e. moderately high brace/chord diameter ratios), and (2) joints with β = 1.0 having low γ. However, it is shown that present guidance may be optimistic for low γ joints with β < 0.9. The new capacity formulations proposed in this paper correct these deficiencies. As one example, the new formulations give an increase of 60% in capacity compared to existing guidance for a joint with β = 1.0 and γ = 10, not untypical of many joints in service. In the near term, the paper may be most appreciated by those involved with structural integrity assessment studies. There have been some recent examples where existing guidance has indicated that some primary structural joints are under-strength. This has prompted extensive numerical work to prove the adequacy of the joints. A worst case scenario would be the implementation of unnecessary offshore strengthening work.
Development of Ice Class Arc4 MK III™ Type LNG Carrier
Authors: Suh Yongsuk , Jang Kibok , Ito Hisashi , Park Seungmun , Han Sungyong , Appolonov E. M. , Shaposhnikov V. M. , Nesterov A. B.
Published: July 2009

It is a very challenging work to design 208K Arctic LNG carrier, since LNG carrier requires high reliability for the structural safety and the environment of Arctic region is known to be very severe. Therefore, special attention should be paid for the verifying the structural safety of LNG carrier particularly with regard to LNG leakage. In this paper, the safety of the hull structure and cargo containment system of 208K MK III™ type LNG carriers with Arc4 is investigated based on the direct calculation of ice loads as well as wave loads. Several scenarios like design ice load, accidental ice load, ramming, entrapment and extreme wave are considered. From the whole investigation, it is clear that the developed vessel — 208K MK III™ type LNG carrier with RMRS Ice class Arc4 — has enough strength and is safe to be operated in Arctic region.
Wave Measurements Using an Air Pressure Gauge
Authors: Bacellar Mendes Leonardo Brantes , Paiva Nunes Luis Manoel , Penteado Dio´rgenes , Lima Jose´ Antonio Moreira
Published: July 2009

An equipment for wave and tide measurements using an air pressure gauge was developed and tested in a Brazilian coastal site (Ilha Grande Bay Maritime Terminal, Lat 23° 03’ 22” S/ Lon 44° 14’ 07” W) for 18 months. The main properties of this equipment were the low production costs and the improved maintenance procedures required by a dry sensor fixed over the sea water level. Data were analyzed using a standard Fast Fourier Transform (FFT) algorithm and the results were very good. As an example of the adequate spectral resolution attained with the analysis methodology, results from a bimodal sea state will be presented, the first peak with period of 5.43 seconds and the second one with a period of 8.30 seconds.
Nonlinear Dynamics and Internal Resonances of a Ship With a Rectangular Cross-Section in Head Seas
Authors: Kleiman A. , Gottlieb O.
Published: July 2009

We investigate the nonlinear dynamics and internal resonances of a ship with a rectangular cross-section in head seas. We employ an asymptotic averaging method to obtain the slowly varying system evolution dynamics for the weakly nonlinear response, complemented by numerical integration in the strongly nonlinear regime. This combined approach resolves both parametric instabilities and internal resonances induced for both weak and finite nonlinear interactions, and culminates with criteria for orbital stability thresholds describing the onset of quasiperiodic response and magnification of energy transfer between coupled pitch-heave and ship roll that can lead to capsize.
Understanding Passenger Ship Evacuation Through Full-Scale Human Performance Trials
Authors: Brown Rob , Boone James , Small Graham , MacKinnon Scott , Igloliorte Gareth , Carran Andrew
Published: July 2009

IMO MSC circular 1033 [1] outlines the guidelines for evacuation analyses of new and existing passenger ships. This requirement coupled with recent advancements in computer technology has lead to the development of sophisticated computer-based simulation of the evacuation process on passenger ships. In order for these simulation tools to provide accurate and useful results, it is imperative they use realistic data for passenger movement throughout the evacuation process. However, due to the nature of ship abandonment, quantifying human performance in actual abandonment situations is very difficult. For this reason, simulation inputs must rely on results of controlled, well-defined experiments. This paper outlines experiments conducted to quantify human performance during abandonment using a variety of life saving appliances for ambulatory and non-ambulatory individuals wearing personal floatation apparatus. Evacuation analysis using commercially available software with these data is also presented as it relates to improving ship design for evacuation of non-ambulatory persons.
Novel Measurement System With Optical Fiber Sensor for Strain Distributions in Welded Tubular Joints
Authors: Murayama Hideaki , Kageyama Kazuro , Ohara Kohei , Uzawa Kiyoshi , Kanai Makoto , Igawa Hirotaka
Published: July 2009

Defects and damage in a structural joint can trigger a critical degradation or collapse of the structure. Among joints, welded joints have many uncertainties, such as remaining stress, initial defects, and heat-affected zone. Such uncertainties in a welded joint can also induce a strain fluctuation, when they are subjected to a load. Conversely, the strain fluctuation along the weld line may represent the presence of uncertainties in the welded joint. This means that monitoring strain distribution along the weld line can be good way to assess their integrity and improve reliability of the structure. We have developed a novel distributed strain measurement technique which can measure strain distributions along fiber Bragg gratings (FBG) in an optical fiber and has the high spatial resolution and we applied it to strain monitoring of a welded tubular joint. The spatial resolution o is less than 1 mm and it was confirmed by measurement simulations and experiments. Then, we measured the strain distributions along the weld line of the tubular joint of a steel pipe subjected to a tensile load by the developed measurement system. We could successfully measure the development of the strain distribution along the weld line, where the sharply fluctuating strain distributions resulting from some defects were observed. In this paper, we describe the measurement principle and performance of the optical fiber sensor, and then show the results of strain monitoring in the welded joint.
Strength Analysis of a RO-RO SWATH Ship Deck Layout
Authors: Iancu Paulina , Pacuraru Sandita
Published: July 2009

The purpose of the paper is to obtain the loads that occur in the connecting deck of a multihull ship, considered on a beam wave. Therefore, is written and used a macro command for obtaining the displacement distribution in order to simulate the bending generated by the beam waves loading. A strength analysis of the loaded connecting deck layout is also performed, to obtain the loads that act upon the structure. In order to determine the stress hot spots and to compare the stresses to the yield point, a linear static analysis is considered.
PIV on Inclined Cylinder Shaped Fish Cages in a Current and the Resulting Flow Field
Authors: Harendza Astrid , Visscher Jan , Gansel Lars , Pettersen Bjo̸rnar
Published: July 2009

The present experimental investigation focuses on the flow structure around short free end cylinders with an aspect ratio of L/D = 3 at a Reynolds number of Re = 5000. Cylinders with varying degrees of inclination and porosity were tested in a towing tank, acting as models for fish farm cages. According to studies of fish cages at commercial Norwegian fish farms, the inclination angle of the structure change up to 25 degrees from the vertical when exposed to a current. Cylinders with porosities of 0% and 75% were tested, the latter representing fish cage netting with fouling. To visualize the flow around the cylinders, 2- and 3-Component (2C and 3C) Particle Image Velocimetry (PIV) was used. The effects of inclination and porosity on the three-dimensional flow field will be described and discussed.
Estimate of Storm Induced Beach Erosion Through the ETS Approach
Authors: Musumeci Rosaria E. , Faraci Carla , Arena Felice , Foti Enrico
Published: July 2009

In the present paper the risk of beach erosion is evaluated by applying the Equivalent Triangular Storm (ETS). The selected case study is ‘La Plaja’ beach located in the South of Catania, Sicily. The proposed approach has shown that when the ETS model is applied, a shoreline retreat has been found which on average overestimates the one obtained by means of actual storm data of about 35%. The model has been applied for the determination of the return period of shoreline recession due to beach erosion during extreme events in order to recover risk maps, which can provide useful information in the planning of coastal interventions. Finally the model has been applied to predict the shoreline retreat in the presence of a submerged breakwater, confirming that the introduction of such coastal protection work strongly limits the risk of coastal erosion.
Elastodynamic Analysis of Towed Cable Systems by Global Nodal Position Vector Finite Element Method
Authors: Zhu Zheng H. , LaRosa Michael , Sun Feng J.
Published: July 2009

The handling and control of towed cable and body systems onboard surface ships and submarines presents a significant technical challenge to design engineers in the defense and ocean industries. The current approaches rely heavily on the empirical methods and the time-consuming and costly prototype testing. Computer simulation provides a cost effective way to reduce the high risks associated with the towed cable/body system. However, the current dynamic analysis of towed cables is mostly done by the finite difference (FD) method in stead of the finite element (FE) method that is widely used in almost all engineering fields. This paper presents an alternative FE method to simulate the dynamics of towed cable and body system, in which the large rigid body motion is coupled with small elastic deformation. The newly derived FE method is formulated in terms of element nodal positions, which is different from the existing FE methods that use displacements. The alternative FE method solves for the cable position directly in order to eliminate accumulated numerical errors arising from existing FE methods that solve for displacements first in order to obtain the cable position over very long period of time. The alternative FE formulation is implemented and applied to real applications to demonstrate its robustness by comparing simulation results with the experimental and sea trial data.