bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Prediction of Thruster-Thruster Interaction
Authors: Bosland R. , Dijk J. M. , Huijsmans R. H. M.
Published: February 2010

Many vessels deploying offshore activities nowadays are dynamically positioned by multiple azimuth thrusters instead of anchors. The multiple propulsor set up, gives a considerable flexibility to work fast and accurate. Due to the fact that the thrusters are positioned relative close to one another their performance is influenced. Normally to quantify this influence and take into account in the DP control algorithm, elaborate experiments have to be performed. To optimize the results a robust numerical flow solver is developed to predict the interaction effects. The program is used to optimize the effort put into these experiments. The developed propeller interaction model is a first order potential based panel method, which uses zero order doublets and sources panel elements. This method is selected to prove the main objective of this research that; Although the slipstream of a thruster has a very turbulent character the interaction can be modeled without taking the viscosity into account as long as an accurate distorted flow field behind a propeller can be predicted. At the 2nd thruster the distorted flow field due to the 1st thruster is modeled by means of two wake field models; a linear potential wake model and an empirical turbulent jet model. Due to the intersection of wake and body panels at the 2nd thruster, numerical instabilities occur at the collocation points. These instabilities are removed by applying a realistic vortex model instead of the analytic vortex model which has infinite velocities in the core. The second problem is to capture the divergent and subsiding character of a propeller wake field by means of a linear potential wake model. This problem is resolved by validating the region for which the results are still accurate. From the results it is concluded that the thruster interaction propeller model coupled to the turbulent jet wake field yield accurate thruster interaction results. For the linear potential wake field results are promising but adaptations are needed to improve the prediction of the divergent and subsiding character of the physical wake field.
Ship Motion Instabilities in Coastal Regions
Authors: Lin Ray-Qing , Kuang Weijia
Published: February 2010

Ship motion instabilities occur much more frequently in coastal regions than in the deep ocean because both nonlinear wave-wave interactions and wave-current interactions increase significantly as the water depth decreases. This is particularly significant in the coastal regions connecting to the open ocean, since the wave resonant interactions change from the four-equivalent-wave interaction in deep water to the interactions of three local wind waves with a long wave (e.g. swell, edge waves, bottom topography waves, etc.) in shallow water [1, 2], resulting in rapid growth of the incoming long waves. In this study, we use our DiSSEL (Digital, Self-consistent, Ship Experimental Laboratory) Ship Motion Model [3,4,5,6] coupled with our Coastal Wave Model [1,2,11] and an Ocean Circulation Model [7] to simulate strongly nonlinear ship motions in coastal regions, focusing on the ship motion instabilities arising from ship body-surface wave-current interactions.
Progressive Wrinkling and Collapse of Pipes Due to Axial Cycling
Authors: Jiao R. , Kyriakides S.
Published: February 2010

Pipelines buried in trenches and covered by soil are essentially under full axial constraint. Under such conditions, a temperature change resulting from the passage of hot oil coupled with high internal pressure can plastically deform the pipe. If the line is relatively thin the compression can induce axisymmetric wrinkling. Mild wrinkling is benign, but at higher strain levels it leads to collapse by localized wrinkling. During a lifetime of 20 or more years, lines experience many startup and shutdown cycles (∼100). This work investigates whether a tube that develops small amplitude wrinkles can be subsequently collapsed by persistent cycling. The problem is investigated experimentally using SAF2507 super-duplex steel tubes with D/t of 28.5. The tubes are first compressed to strain levels high enough for mild wrinkles to form; they are then cycled axially under stress control about a compressive mean stress. This type of cycling usually results in material ratcheting; here it is accompanied by accumulation of structural damage due to the growth of the amplitude of the initial wrinkles. The tube average strain initially grows nearly linearly with the number of cycles, but as a critical value of wrinkle amplitude is approached, wrinkling localizes, ratcheting grows exponentially and the tube collapses. The rate of ratcheting and the number of cycles to failure depend on the initial compressive pre-strain and on the amplitude of the stress cycles. However, collapse was found to occur when the accumulated average strain reaches the value at which the tube localizes under monotonic compression. A custom shell model of the tube with initial axisymmetric imperfections, coupled to a cyclic plasticity model is used to simulate successfully the series of experiments performed.
Pipeline VIV: Analytical Solution, Experiments and Parameter Identification
Authors: Cunha Sergio B. , Matt Cyntia G. C. , Morooka Celso K. , Franciss Ricardo , Tsukada Raphael I.
Published: February 2010

The study presents a closed-form solution for the vibration of a simply-supported beam due to vortex shedding, assuming linear elasticity and considering fluid damping. The in-line and cross-flow fluid forces are coupled to the beam equation as harmonic nonhomogeneous terms. Experimental results of 2 DOF VIV of a flexible small scale pipe in a uniform stream are presented for perpendicular an oblique (at 60 degrees of the translation direction) pipe. The range of relative velocity is from 1 to 10. The performance of two fluid damping models (Venugopal, 1996; Blevins – modified, 1990) is evaluated by comparing their predictions to the measurements of the in-line and cross-flow oscillations. Finally, ranges for in-line and cross-flow force coefficients are proposed and compared to the literature.
On the Reliable Modeling of the Collapse and Post-Collapse Behavior of Pipelines
Authors: Toscano Rita G. , Dvorkin Eduardo N.
Published: February 2010

Finite element simulations are nowadays a standard industrial tool for exploring the effect of manufacturing tolerances on the collapse and collapse propagation pressure of tubular goods. Hence, it is of the highest importance that sound computational techniques are used and that the model results are validated using experimental results. Regarding the modeling of steel pipes collapse and post-collapse behavior, in this paper we discuss: applicability of 2D models; shell elements for the 3D models; nonlinearities to include in the models; material modeling; modeling of residual stresses; boundary conditions for simulating different pressure tests; code verification and results validation. Regarding the link between production process and manufacturing tolerances we briefly review some results that we obtained for the case of the UOE process.
Dynamic Response Characteristics of a Floating Wind Turbine Tower at Low Response Frequency
Authors: Johanning Lars
Published: February 2010

This paper presents experimental and numerical hydrodynamic load and damping results on a surface piercing pivoted circular cylinder, representing a monopile of a floating Marine Renewable installation (Spar-Buoy concept). The resulting load and damping characteristics are applied to predict the response characteristic of the pile and compared with experimental results. The main consideration is given to the characteristic of the cylinder due to steep wave action in the pitching mode. The experiments were conducted in the wave tank at the University of Glasgow using a cylinder model with a diameter of D = 0.21m that was constructed at the Imperial College London, to provide a structural to wave frequency ratio of 2 and 3. The outcome from the investigation supports the importance of the dynamic response to the successful operation of a deep water wind turbine installation.
Key Materials and Systems for the Use of Renewable Energy in the Form of Methane
Authors: Hashimoto Koji , Kato Zenta , Kumagai Naokazu , Izumiya Koichi
Published: February 2010

Extrapolation of primary energy consumption of the world between 1990 and 2005 to the future revealed the complete exhaustion of oil, uranium, natural gas and coal reserves on the Earth in 2034, 2040, 2040 and 2054, respectively. We have been proposing global carbon dioxide recycling to use renewable energy for all people in the whole world. The electricity converted from renewable energy will be used for production of hydrogen by seawater electrolysis. Hydrogen, for which no infrastructures of transportation and combustion exist, will be converted to methane by the reaction with carbon dioxide captured by energy consumers. Among systems in global carbon dioxide recycling, seawater electrolysis and carbon dioxide methanation have not been performed industrially. We created energy-saving cathodes for hydrogen production and anodes for oxygen evolution without chlorine formation in seawater electrolysis, and ideal catalysts for methane formation by the reaction of carbon dioxide with hydrogen. This paper reviews the characteristics and performance of these materials in the systems.
Experimental Investigation of the Validity of Linear Theory to Assess the Behaviour of a Heaving Point Absorber at the Belgian Continental Shelf
Authors: De Backer Griet , Vantorre Marc , De Beule Kim , Beels Charlotte , De Rouck Julien
Published: February 2010

The results of an experimental investigation on a heaving point absorber are presented. The physical tests are used to validate numerical simulations of the behaviour of the point absorber based on linear theory in the frequency and time domain. Floater response and power absorption are evaluated in regular and irregular waves representing a mild wave climate. A good correspondence is found between the physical and numerical test results. In irregular waves the difference between numerical and experimental power absorption is generally smaller than 20%. In regular waves the correspondence is good as well, except in the resonance zone; i.e. when the natural frequency of the buoy is tuned towards the resonance frequency of the incident wave. In this case, non-linear effects such as viscosity and a non-linear hydrostatic restoring force become important due to the high velocities and motion amplitudes of the point absorber. However, because of these large amplitudes, pure resonant cases are often not preferred in practical applications. In general it is concluded that the numerical results are in good accordance with the experimental results and can be used to predict the point absorber behaviour in mild energetic waves in non-resonance conditions.
Modeling of Flow in a Near-Wellbore Network
Authors: Thompson Leslie , Brekke Kristian
Published: February 2010

We consider steady-state multiphase flow in the near-well region of a completed horizontal well. The flow topography in this system is such that many alternate paths are available for fluid to travel from the reservoir to the producing vertical wellbore. Predicting and controlling this flow is essential to optimizing recovery from the reservoir. We treat the system as a pipe network. We decouple the mass conservation and pressure equations and solve for the phase splits at each junction in the network under the assumption that there is complete mixing at each branch point. Thus, the gas-liquid ratio (GLR) and water oil ratio (WOR) of each stream exiting a given network junction is constant and is determined by the quality of the streams entering the junction. (This assumption is reasonable since the flow paths in the “network” are short.) We use Newton iteration to solve the pressure equations. The resulting algorithm is fast and robust, so that it is well suited for coupling with a reservoir flow simulator. We illustrate the method by presenting an example.
The Improvement of k-ε Model in the Turbulent Wave Boundary Layer
Authors: Zhu Yuliang , Ma Jing , Dong Peipei
Published: February 2010

Numerical model is one of the means for investigating turbulent wave boundary layer. Many scholars have used various eddy-viscosity models to simulate wave turbulent boundary layer flow. On the basis of analyzing existing models, the article uses more reasonable boundary condition to establish an advanced model of turbulent wave boundary layer by k-ε model. Past models have two problems. Firstly, the calculation area is not united since one of the calculation areas is all-water depth and another is boundary layer thickness. Aimed at this problem, this model makes a sensitivity analysis of velocity and eddy-viscosity for various calculation area, which turns out that velocity inside the boundary layer is low-sensitive while the eddy-viscosity is high-sensitive to the change of calculation area. Secondly, a new integration adjust coefficient p is presented to solve the five empirical constants which are difficult to adjust in k-ε model. Although these five empirical constants have recommended value, the universality is not good. In order to obtain better eddy-viscosity value, many methods were suggested to get these five empirical constants, however, most are very complicated. In this article, adjust coefficient p is put before the diffusion item in the velocity equation, and p is a little bit smaller than 1. The result indicates that a reasonable eddy-viscosity can be easily adjusted using this method. The modified model has overcome some shortcomings of the previous models, and gets a better simulation effect.
Experimental Study on Water Flow Characteristics of Conical Floating Structure
Authors: Tanaka Hiromichi , Sumita Akinori , Suzuki Atsushi , Manabe Yasuhiro
Published: February 2010

This research consisted of an experimental study regarding the water flow characteristics of a conical floating body with wave-absorbing and water-flow features. The conical floating body is a conically shaped floating structure comprising 12 sheets of convergence banks and a cylindrical tank in the center to catch the overtopping waves. The experiment employed the No. 3 machine model to investigate the water flow characteristics for the two water-flow methods of (a) the flow of water to the receiving tank and (b) free discharge, by changing the following parameters: wave condition, wave overtopping head, and duct length. The results obtained indicated that the maximum water-flow efficiency was 46.5%, and that water-flow efficiency was altered by duct length.
Analysis of Social Background and Classification by Geopolitical Function of Floating-City Project Proposals
Authors: Kato Shimpei , Kondo Takeo , Yamamoto Kazukiyo , Fukunaga Taketo
Published: February 2010

Many floating city projects, both domestic and overseas, have been proposed since the 1960s. However, most of them have never gotten off the ground except for those that found a shape in Japan, all of which were reclamation or landfill types filling the gap of an urban function in the coastal land areas. In this research, we analyzed the social background of offshore cities using a bibliographical survey, concomitantly conducting interviews, extracting the factors of size, function, etc., of the sea city projects, classifying the projects by geopolitical function by using quantification theory, and from the results we are making a proposal as the guidepost indicating the feasibility and directionality of developing the offshore city of the future.
Global Design and Analysis of Umbilical in Offshore Applications
Authors: Qiu Weiyong , Cao Qiang , Librino Filippo , Hahn Guillermo , Stanton Paul
Published: February 2010

An umbilical is an assembly of fluid conduits (thermoplastic hoses and steel tubes), cables (electrical and fibre optic), and power cores, joined together for flexibility and over-sheathed, with or without armouring, for mechanical strength and stability. The emphasis of this paper is on the global configuration design and analysis of offshore umbilicals. The extreme and interference analysis methodologies are presented. One example is given for the application of very small OD electrical umbilical in shallow water in West Africa. The proposed global configurations are presented. Another example is presented for the application of a hydraulic umbilical in deep water in the Gulf of Mexico. The selection of the global umbilical configuration in deep water depends on the host vessel. In other words, the vessel motion characteristics may dominate the umbilical configuration selection for the deep water application. This paper also deals with the influence of the bottom current on the global design of the umbilical in deep water. It can be concluded that an optimized umbilical global configuration, which meets the strength and interference design criteria, can be achieved for the application of a small OD electrical umbilical in shallow water in West Africa as well as for a steel tube designed hydraulic umbilical in deep water in the Gulf of Mexico.
The Use of Streamed Digital Video Data and Binocular Stereoscopic Image System (BiSIS) Processing Methods to Analyze Ocean Wave Field Kinematics
Authors: MacHuchon Keith R. , Wessels Wehan J. , Wu Chin H. , Liu Paul C.
Published: February 2010

The kinematics of short crested steep and breaking waves in the ocean is a subject that is best studied spatially, in the time domain, to obtain a good understanding of the multi-directional spreading of energy, which is dependant on strongly non-linear wave interactions in the system. The paper will cover the collection, recording and processing of streamed sea surface image data, obtained simultaneously from multiple digital video cameras, for analysis using stereoscopic image processing methods to provide information on the kinematics of ocean wave fields. The data streaming architecture, which will be reviewed, incorporates an advanced laptop computer and two to three stand-alone digital video cameras which are all linked through a gigabit ethernet network connection with sufficient bandwidth to simultaneously transfer the image data from the cameras to hard drive storage. The modifications to the laptop computer comprise the provision of increased processing capacity to enable it to accept and process large IP frames simultaneously. The system has the capacity to continuously record images, at a rate of up to 60 frames per second, for periods of up to one hour. It includes an external triggering mechanism, which is synchronised to a micro-second, to ensure that stereo pairs of images are captured simultaneously. Calibration of the cameras, and their stereoscopic configuration, is a critical part of the overall process and we will discuss how ill-conditioned and singular matrices, which can prevent the determination of required intrinsic and extrinsic parameters, can be avoided. The paper will include examples of wave field image data which has been collected using streamed digital video data and Binocular Stereoscopic Image System (BiSIS) processing methods. It will also give examples digital video images and dimensional wave field data which has been collected and processed using the Automated Trinocular Stereoscopic Imaging Systems (ATSIS) methods. Both of these systems provide a valuable means of analysing irregular, non-linear, short crested waves, which leads to an improved understanding of ocean wave kinematics.
Effective Medium Properties of Periodic Elastic Layers by Homogenization
Authors: Liu Ying-Hong , Chang Chien C. , Kuo Chih-Yu
Published: February 2010

In this study, we examine effective modes of acoustic waves in periodic solid layers embedded in ideal or viscous fluids. In particular, at the long-wavelength limit, a three-scale homogenization analysis is developed to derive the effective group velocities in analytical forms for the shear-vertical (SV) waves as well as for the longitudinal-shear-horizontal (P-SH) waves. It is found that propagating modes, i.e., modes with real group velocities, may be supported even if the fluid phase is viscous. A criterion for the existence of a vanishing effective viscosity is derived based on composite medium constants and the filling ratio of the fluid phase. The critical filling ratios at which an evanescent mode changes to a propagating mode are given for various solid-water systems. Finally, we would like to acknowledge that the analysis presented here benefited greatly from the article drawn attention to the first author by Prof. Mei some ten years ago: “C. Mei, J-L. Auriault, and C. O. Ng (1996) Some Applications of the Homogenization Theory, Advances in Applied Mechanics, Vol. 32, edited by J. Hutchinson and T. Y. Wu, Academic Press, New York.”
Observations of the Boundary Layer Characteristics at the Yangtze Estuary
Authors: Hao Jialing , Zheng Jinhai , Zhang Wei
Published: February 2010

Measurements of the flow velocity profiles through one tidal cycle were taken in the Yangtze Estuary. The flow velocity profile during the experiment was characteristic of a tidal boundary layer growing through the tide, and with increasing velocity, especially on the accelerating flood tide. Due to the bed friction, the near bottom flow, which forms the bottom boundary layer, is different from that of the water body far from the bed in estuarine and coastal waters. In near bottom layer, due to the frequent flux and momentum exchanges between the flow and the bed, the study of near bottom plays an important role in vertical mixing of water, sand, temperature, salinity and the process of bed-load movement. Some scholars point out that due to the acceleration or deceleration action of tide, the flow structure deviates from traditional logarithmic law in estuary, coast or other near shore waters. In a previous study by the authors, it was shown that the measured vertical profile of tidal current agrees better with a logarithmic-linear model than logarithmic model through the theoretical derivation and case verification. The friction velocity u* and the roughness length z0 are calculated based on a logarithmic-linear tidal current velocity model and compared with that of using traditional logarithmic model also. Some of the sample sites were selected to analyze the distribution of the friction velocity u* and the roughness length z0 with the temporal and spatial variation. The derivation of the boundary layer parameters was restricted to profiles when the mean current speed almost increased with height and is greater than 0.3 m/s to exclude the periods around slack water. From profiles that showed an increasing speed with height, the parameters u*, z0 and CD are estimated and presented here. The methods of deriving the shear stress from vertical profiles are discussed and the drag coefficients are presented.
Residual Stress Measurement on a Narrow Gap Dissimilar Metal Weld Pipe
Authors: Ficquet Xavier , Chidwick Laurie , Gilles Philippe , Joly Pierre
Published: February 2010

Prior knowledge of the magnitude and distribution of residual stresses in welded components is essential if a cost effective analyses of the integrity of the components is to be made. AREVA NP has recently developed, for EPR applications, narrow gap welding techniques, for joining ferritic low alloy steel heavy section components to austenitic, stainless steel piping systems, in nuclear reactors. An appraisal of available measurement methods was carried out and two residual stress measurement techniques were used to obtain through-thickness residual stress distributions in a fully circumferential narrow gap welded pipe, the neutron diffraction, which is not presented in this paper and the deep hole drilling (DHD) method. The DHD method was used to obtain the axial and hoop residual stresses along the weld centreline and on the heat affected zone in the ferritic and stainless steel sides up to depths of about 40mm from the outer surface of the pipe. The measured residual stress distribution in the weld centreline is compared with representative residual stress distribution provided in UK safety assessment procedures. It is found that the current safety assessment procedures BS 7910:2005 and R6 are conservative. The DHD measurements were made only at limited points in and adjacent to the circumferential weld. In order to estimate the complete residual stress distribution present in the pipe, a measurement mapping procedure using finite element (FE) analysis was implemented. Therefore this paper also provides the estimates of the full residual stress state present in the pipe based on the mapping procedure.
Numerical Simulation of Interface Time Evolution by Oriented Lagrangian Particles and Level-Set Method
Authors: Ianniello Sandro , Di Mascio Andrea
Published: February 2010

A new computational approach for tracking evolving interfaces is proposed. The procedure is based on the copuling of lagrangian massless particles and the standard Level-Set methodology, and the use of evolution equations for fundamental vector and tensor quantities related to the geometrical properties of the interface Γ. In particular, the normal vector n and the second fundamental tensor ∇n are linked to the particles and advected with them; in this way, the particles can be located upon Γ and enable a step–by–step calculation of the Level–Set function φ through a direct solution of the eikonal equation. No transport equation and reinitialization procedure for φ have to be taken into account and the usual numerical diffusion affecting the Level–Set approach is removed. The method is easy to code and carries out an accurate reconstruction of the front, limited only by the spatial resolution of the mesh.
Estimation of Small-Scale Vertical Diffusivity for CO2 Injected in the Deep Ocean
Authors: Hirabayashi Shinichiro , Sato Toru
Published: February 2010

In this study, vertical diffusivity, the scale of which was O (10 m), at a particular site in the deep ocean was estimated by using numerical simulations with forcing low-wavenumber components, which had been reproduced from measurement data. Spatial information of velocity field was reproduced by spectral analysis of 4 sets of time-series measured simultaneously at different places in the real ocean. In order to estimate finer-scale structures, which are necessary to obtain statistical quantities such as energy dissipation rate, large eddy simulations were carried out with forcing low-wavenumber components of velocity reproduced in the spectral analysis. The low-wavenumber components generated by the nonlinear interaction of forced components and resolved components were successfully removed from the computational domain by introducing a partial spectral filter in place of the conventional FFT filter. Vertical diffusivity was estimated by using the energy dissipation rate of the reproduced flow field, which was 3.3×10−5 m2s−1 on the time average.
A New Top Connection System for Steel Catenary Risers
Authors: Silva Dantas Claudio Marcio , de Sousa Jose´ Renato Mendes , de Sousa Fernando Jorge Mendes , Queija de Siqueira Marcos , Masetti Isai´as Quaresma
Published: February 2010

PETROBRAS has been developing several studies in order to verify the structural feasibility of SCRs connected to production units such as FPSOs, semi-submersible and monocolumn platforms. Due to the great stresses developed at the top region as a consequence of the platforms rotation movements, robust stress joints or flex joints are always required to connect the SCRs to the platforms. However, those components may add high costs to any project, mainly where titanium is required. In attempt to avoid this fact, the objective of this work is to present a new top connection system called “Suspender”. This system is composed by the SCR, a mooring line segment, a flexible jumper and a “Y” shaped steel connector, and has the advantage of reducing the transmission of bending moments from the platform to the SCR. The performance of this alternative was compared to a more conventional one, composed by a SCR and a flex joint, and the obtained results indicate that this new system reduces the maximum stresses at the top region without changing the SCR behavior at the TDZ. It is also possible to extend the fatigue life by changing the SCR configuration.
Near-Wall Turbulent Transport Knowledge for Suitable Flow Assurance Strategies
Authors: Zeinali Hossein , Toma Peter , Kuru Ergun
Published: February 2010

Gas-liquid transportation from the deep ocean floor level to wellhead and, then, to platforms and land processing units is often impeded by wax and hydrates deposits; sand erosion and corrosion-related being frequently encountered. During the last decades it was shown that apparently different problems such as sand erosion and deposition-removal of paraffin during turbulent pipe transportation are the effect of near-wall flow transport related to burst-sweep specific turbulent activity. Coherent structures visualized as a sequence of (in) bursts and outburst sweep actions has already been suggested as an important factor for understanding aging of the paraffin deposit and the deposition-removal balance controlling the grow of deposit. This paper, using published models, investigates the effect of near-wall turbulence on removal of small-size particulate matter, first through direct measurement of burst activity, then, using fine sand and glass beads transported as moving bed during turbulent flow condition. Lack of experimental data for assessing the effect of turbulent liquid pipe flow on burst activity for removal of fines created challenging problems. Those include direct assessment of burst frequency and measurement of the rate of fine sand grading and on-line sampling and measuring the rate of fine removal during sand bed or lenticular deposits transportation. Laboratory work uses a Particle Image Velocimetry (PIV) instrument to observe and quantified the burst activity as it progresses from the pipe wall to the turbulent core flow. Experimental data are closely compared to existing literature models; in addition the present laboratory measurements allow for describing the dynamic of a burst as it evolves from the pipe wall to turbulent core regions. The frequency of burst removal is further compared with changing of size distribution during the sand bed-slurry transport stage of this work. Results obtained so far at the University of Alberta with the aid of an experimental loop designed and operated for observing and quantifying selective (size-density) radial-axial transportation of fines are discussed and summarized. It is suggested that the experimental data on fines removal and deposition, particularly related to near-turbulent structure activity, is important for understanding and mitigating a broad range of near-wall turbulent-related flow assurance problems.
Fracture Mechanics Evaluation of Pipes Subjected to Combined Load Conditions
Authors: Cravero Sebastian , Bravo Richard E. , Ernst Hugo A.
Published: February 2010

For certain applications, pipelines may be submitted to biaxial loading situations. In these cases, it is not clear the influence of the biaxial loading on the fracture mechanics behavior of cracked pipelines. For further understanding of biaxial loading effects, this work presents a numerical simulation of ductile tearing in a circumferentially surface cracked pipe under biaxial loading using the computational cell methodology. The model was adjusted with experimental results obtained in laboratory using single edge cracked under tension (SENT) specimens. These specimens appear as the better alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The negligible effect of biaxial loadings on resistance curves was demonstrated. To guarantee the similarities of stress and strains fields between SENT specimens and cracked pipes subjected to biaxial loading, a constraint study using the J-Q methodology and the h parameter was used. The constraint study gives information about the characteristics of the crack-tip conditions.
Transient Wax Gel Formation Model for Shut-In Subsea Pipelines
Authors: Ekweribe Chiedozie , Civan Faruk
Published: February 2010

Physics of wax gel formation during shut-in is analyzed and described over a cross-section of a typical subsea pipeline. Two regions are identified during this process: the liquid and gel regions. Phase transition is assumed to occur at the liquid-gel interface. Unsteady-state heat and mass transfer models are proposed for each region. Two diffusion streams are evaluated: the dissolved wax molecules moving from the pipe center towards the wall due to temperature gradient and subsequently concentration gradient and the wax molecules diffusing from the liquid-gel interface into the gel deposit. This model is essentially the modification of the model given by Bhat et al [1] which considered transient heat transfer and neglected mass transfer of wax molecules through the gel deposit and the model by Singh et al [2] which considered transient mass transfer of molecules with carbon numbers higher than the critical carbon number (CCN) necessary for wax diffusion into gel deposit but did not consider transient heat transfer effects during the cooling process. This paper presents a transient-state formulation circumventing the limitations of these previous models and better represents the true cooling and gelation process occurring in a shut-in subsea pipeline filled with waxy crude.
The Status of Marine Mining Worldwide
Authors: Morgan Charles L.
Published: February 2010

Metals are fundamental components of modern society worldwide, and, despite the current economic downturn, we know we will be faced with ever increasing demands and ever-shrinking supplies. Efforts to achieve sustainable supplies of minerals must include efforts to expand the supply. About 60% of the ocean surface consists of the ocean floor, so it is reasonable to expect that deep ocean minerals could contribute significantly to the world supply. Human efforts to recover minerals have thus far concentrated almost exclusively on land-based resources, so it is reasonable to postulate that marine minerals might offer better prospects for future mineral supplies than land prospects. Currently, we know of at least six separate categories of marine minerals: 1. Aggegrate sand and gravel deposits; 2. Placer deposits of relatively high value minerals (gold, diamonds, tin, etc) hosted in aggegrates; 3. Biogenically derived phosphate deposits; 4. Sediment-hosted (manganese nodules) and hard-rock hosted (ferromanganese crusts) ferromanganese oxide deposits; 5. Sediment-hosted methane hydrate deposits; and 6. Hydrothermally derived sulfide deposits of copper, gold, nickel, zinc, and other metals. Thanks primarily to the engineering developments made by the offshore oil industry and the computer-science advances that have revolutionized much of modern society, the technology is in place for most of the tasks of deep seabed mining. The objective here is not to provide a general status update regarding marine minerals technology, but simply to demonstrate, using the best example available to date (the Nautilus Minerals venture in the Territorial Waters of Papua New Guinea) that the technology is in place and ready to go. Development of marine minerals has both the curse and blessing of taking place in the ocean. Since the 1970’s and before, the marine environment has taken on a public aura reserved more commonly for religious beliefs. This aura poses substantial obstacles to any marine development efforts. At the same time, a basic advantage of marine mineral developments is that nobody lives there. Thus, marine mining activities will not conflict with most normal human activities. Marine mining proposals should be subjected to thorough impact assessment analysis, but it is also critical that policymakers take steps to provide a level playing field for marine developments that encourages objective comparisons with alternative land-based proposals for supplying needed mineral resources. Governments should foster reasonable access to the marine mineral resources under their jurisdiction while also supporting incentive policies and related research programs.
Experimental Investigation on the Dynamic Response of Density-Stratified Fluid in a Submarine Trench
Authors: Hwung Hwung-Hweng , Hsu Wen-Yang , Liu Chi-Min , Yang Ray-Yeng
Published: February 2010

The dynamic response of the generated internal wave as surface water propagating over a submarine trench is investigated in a wave flume. The image processing technique is used to observe the response of density-stratified interface. Two typical distinct phenomena of internal waves were caught in the experiments, which are standing internal waves usually occurred as the incident waves range from 0.6∼0.8 times the length of trench, and the traveling internal waves usually occurred outside this range.
Numerical Simulation of Pipeline VIV for Steady and Unsteady Flow
Authors: Bhattacharjee Pratik , Nielsen Kenny K. , Stewart Graham
Published: February 2010

The ability to predict Vortex Induced Vibrations (VIV) is important for the design and assessment of subsea pipelines lying on the sea-bed and susceptible to spans. Recent advances in CFD methods and the availability of powerful computational resources has made numerical simulation a viable option for VIV prediction. In this paper, an advanced meshing technique which is capable of handling moving boundaries, is used to discretise the fluid domain. This approach, in conjunction with a structural model, is employed to simulate the complex case of VIV in a pipeline in close proximity to the sea-bed. Simulations are carried out using 2-D CFD models for various configurations of sea bed proximity for flow regimes ranging from moderate to high Reynolds numbers and KC numbers in the range 10 to 40. The results obtained are benchmarked with published experimental data and good agreement is obtained. This study demonstrates the feasibility of using CFD models to obtain accurate VIV predictions for subsea pipelines. Future studies will examine more complex flow regimes including random waves and also consider 3D modelling.
Accurate Well-Bore Hydraulics Simulation Considering Non-Isothermal and Liquid-Slippage Phenomena for Multiphase Flow in Oil and Gas Wells
Authors: Michel Guillermo G. , Civan Faruk
Published: February 2010

A review of studies relevant to describing the non-ideal behavior encountered in oil and gas flow through wells is presented. The empirical prediction of liquid holdup and relaxation in time of gas separation from liquid phases are considered as mechanisms for explaining the nonideal behavior. Several features in modeling multiphase flow are discussed. The details of interest are elaborated for each reviewed approach and summarized. An application is presented in order to illustrate the holdup and relaxation profiles for vertical oil wells. The results are obtained by applying a novel formulation for liquid holdup modeling.
Higher Order Resonant Interaction of Surface Waves by Undulatory Bottom Topography
Authors: Alam Mohammad-Reza , Liu Yuming , Yue Dick K. P.
Published: February 2010

Higher order (quartet) Bragg resonance of water waves by bottom undulations and its effect on the evolution of ocean wave spectrum, particularly over continental shelves and littoral zones, are considered. Higher order Bragg resonance can provide a viable mechanism for distribution of (initially confined) energy across the spectrum. Contrary to classical Bragg resonances (Class I and II) where the resonant wave has to have the same frequency as the incident wave, Class III (quartet) Bragg resonance of three free waves and a bottom topography component allow participant waves to have different frequencies. Of particular interest here are higher-order resonances that lead to infragravity wave generation as a result of interaction of regular sea waves with bottom undulations (of the same order of wavelength as the primary waves), and, long/medium surface wave generation by nonlinear interaction between short surface waves and medium wavelength bottom undulations. These mechanisms can accelerate the rate by which energy is damped by the bottom friction. The second mechanism also provides a potential alternative mechanism for explaining microseismic noise observed in shallow waters. We further consider the oblique higher order Bragg resonance. Although for Class I, oblique resonance is less important than normal incidence, it is shown here via illustrative examples and direct simulations that there are strong oblique Class II and III Bragg cases. Inclusion of higher order interactions paves a path for the energy transfer to higher and lower frequencies of an initially narrow band spectrum. Ensuing multiple (exact/near) such resonant interactions can result in the generation of multiple new transmitted/reflected waves that fill a broad wavenumber band eventually leading to loss of order and chaotic motion of water surface.
An Underwater Vehicle for the Tracking Marine Organism “PICASSO”
Authors: Ishibashi Shojiro , Yoshida Hiroshi , Lindsay Dhugal J. , Yamamoto Hiroyuki , Hyakudome Tadahiro , Sawa Takao , Okuno Hikaru , Uemura Takayuki
Published: February 2010

So far, a special net is used to sample marine organism such as planktons in the marine biology. It is called as a plankton-net. However it often breaks the tissue of the marine organism. So scientists of the marine biology demand a good tool to observe the marine organism instead of the plankton-net sampling. On the other hand, an underwater vehicle has been a focus of constant attention in order to observe the marine organism. The vehicle should be equipped with devices to observe the marine organism and measure the sea characteristic. So Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has developed a new underwater vehicle “PICASSO”. It is small size vehicle, but it can be equipped with various observation and measurement devices. And also it can be applied to a small ship as its own support ship owing to its size. In this paper, the outline of PICASSO and its key technologies are described, and results of sea trials carried out until now are shown.
Passive Acoustic Monitoring of Surface Vessel Activity
Authors: Nosal Eva-Marie , Nosal Miloslav
Published: February 2010

Monitoring human activity in remote marine areas is a challenging problem to which acoustic methods present a promising solution. This paper develops and demonstrates automated passive acoustic methods to estimate ranges to surface vessels using a single seafloor-mounted hydrophone. Surface vessels that use echosounders (to navigate or find fish, for example) are especially well suited for passive acoustic monitoring since they use high-energy, narrow-band, short-duration pulses. Examples of surface vessel ranges estimated using echosounder pulses recorded on a seafloor-mounted hydrophone are presented.
Reliability of Fracture Mechanics Approach to Fatigue
Authors: Macia Mario L. , Buitrago Jaime , Kan Wan , Bichon Barron , Moody Jonathan , Hudak Stephen
Published: February 2010

Current fatigue design of fracture-critical components, such as tendons and risers, requires dual fatigue life criteria to be satisfied. The S-N approach includes a safety factor (SF) of 10 on the life of the component, while the fracture mechanics (FM) approach includes a safety factor of 5 on the life through-thickness of an acceptable initial flaw. FM provides critical initial flaw sizes such that suitability of the selected NDE methods and weld acceptance criteria can be established. This paper pertains to a comparative fatigue life reliability study between those two approaches. The objective is to develop a rationale for the selection of a safety factor on fatigue life to use in FM calculations. A reliability-based methodology is proposed and implemented. The SFs for FM are obtained by targeting the reliability obtained in fatigue designs based on historically proven S-N damage approach. Random variables entering both approaches were characterized and a number of weld design cases devised to obtain reliabilities. One important variable is the distribution of initial flaw sizes. For this study, flaw distributions were developed from actual inspection records, accounting for the effects of probability of detection and sizing accuracy of the inspection system, as well as the flaw acceptance criteria during fabrication. Comparisons of reliabilities obtained for designs by both approaches for various quality S-N curves, stress spectra, pipe sizes, and initial flaw sizes indicate that there is ample scope to modify downward the current FM safety factor. However, given the limited scope of this study, it is recommended to asses the FM SF using reliability analysis on a project-specific basis.
The Influence of Waves on Oil Spill Behavior
Authors: Lee Jung L. , Lee D. Y. , Kim I. H.
Published: February 2010

In the present study, we include the wind generated wave module to improve the prediction accuracy of oil spill behavior under the stormy sea condition. The wind waves are simulated by using a new concept of wavelength modulation to enhance broader application of hyperbolic wave model of mild-slope equation type. The Hebei Spirit oil spill movements are accounted for by including the Stokes drift due to weakly non linear waves and simulated with an efficient operational model of GUI environments.
Experimental Evaluation of Separation Methods for a Riser Dilution Approach to Dual Density Drilling
Authors: Shelton John , Smith John Rogers , Gupta Anuj
Published: February 2010

A dual gradient, deepwater drilling system based on dilution of riser mud requires economically separating the riser mud into a low density dilution fluid and a higher density drilling fluid. This study investigated the practicality of accomplishing this separation using hydrocyclones and centrifuges and examined the possible benefits and efficiency of each. The separation experiments were conducted using a laboratory centrifuge and 2 inch hydrocyclones. The laboratory centrifuge was able to separate the riser mud into near ideal densities for dilution and drilling fluid. However, the dense slurry retained in the centrifuge had lower emulsion stability than the feed stream. The hydrocyclones achieved much less contrast in density between the low and high density discharges, but consistently resulted in a beneficial increase in the stability of the mud emulsion in all of the flow streams and had more desirable rheological properties. A qualitative comparison indicates that the hydrocyclone separation system may offer a feasible and desirable alternative to centrifuge separation system.