bluuebunny/crossref_metadata_2025 huggingface dataset:
Offshore Wind Farm Construction: Easier, Safer and More Cost Effective
Authors: Eijssen Marc
Published: November 2011

Converting wind energy into a useful form of energy is one of the fastest growing alternative sources of energy in the present and foreseeable future. At the end of 2009, worldwide nameplate capacity of wind-powered generators was 159 gigawatts (GW). Energy production at onshore, near shore and offshore locations was 340 TWh, which is about 2% of worldwide electricity usage, and has doubled in the past three years and will continue to grow substantially. This growth comprises not only more wind farms, but wind mills with more capacity as well [1–3]. To achieve this growth, (heavy) lift companies and offshore contractors meet various challenges. Since primary cost for producing wind energy is construction, with up to 10 lifts per wind mill, a very competitive environment has been created in which efficient logistic and lifting operations, flexibility, avoiding damage to loads and safety are paramount [4,5]. Appropriate lifting gear provides an essential tool to meet these challenges; especially at offshore locations. Currently, steel wire ropes and grommets are extensively being used as lifting gear during the construction of wind farms, with its low cost being the key driver. But its weight together with the risk for damage to loads and injuries to operators are serious concerns. Synthetic slings, especially those made from polyester fiber, have gained popularity as a way to overcome these concerns. But, such slings are very sensitive to damage, hence its value and risk-avoidance is more and more being questioned; especially considering currently applicable legislation such as the European Machinery Directive 2006/42/EC [6]. With the introduction of high performance fibers, such as Dyneema® (Ultra-High Molecular Polyethylene (UHMwPE) fiber), not “just another synthetic fiber” has been introduced. The use of this UHMwPE fiber in protective sleeves and load bearing constructions holds the characteristics to overcome the concerns of the traditional materials as it has been proven by well-respected lifting companies. Since durability of a synthetic sling is largely determined by the performance of the protective sleeves, this paper comprehensively presents the abrasion, cut and tear resistance improvement created by sleeves made with fibers such as Dyneema®. In combination with its functionality in load bearing constructions and the key elements of the European Machinery Directive 2006/42/EC, this paper proves that Ultralift® roundslings made with Dyneema® provide not only safer and easier but also more cost effective construction (logistics and lifting) operations. So, slings made with Dyneema® have been entrusted to meet the lifting challenges of today and tomorrow.
Fatigue Assessment of Subsea Tree Connectors and Wellheads
Authors: Buitrago Jaime , Krishnan Venkat R. , Sommerfield Paul M.
Published: November 2011

Drilling and workover operations offshore impose fatigue loads on the subsea tree and wellhead due to the riser dynamics. In particular, the connector between the tree composite valve block and the wellhead components may be subjected to fatigue damage. This is primarily due to specific mechanical connector designs, girth welds and thickness or section transitions commonly used in trees and wellheads. The fatigue assessment methodology of subsea tree connectors and wellheads requires a holistic approach involving sequential analyses of the floating vessel, riser, subsea well stack-up, and the wellhead and downhole casing assemblies including cement and soils. In this paper, a methodology for the analysis of each of those assemblies and their interactions is discussed. The methodology reflects ExxonMobil’s experience and offers a balance among analysis efficiency compatible with project and operational constraints, availability and uncertainty of the inputs, and accuracy of the outputs. In general, the methodology is based on dynamic analysis of models to obtain global response loads of the floating unit, riser, and wellhead. Finite element analyses are then used to translate global responses to local stresses and to define SCFs for structural details of interest. The conventional cumulative damage approach is adopted, which provides fatigue lives based on local stresses and fatigue resistance defined by S-N curves. The fatigue resistance of machined components is based on a strain-life model that provides material specific S-N curves.
Development and Verification of a Computational Fluid Dynamics Model of a Horizontal-Axis Tidal Current Turbine
Authors: Lawson Michael J. , Li Ye , Sale Danny C.
Published: November 2011

This paper describes the development of a computational fluid dynamics (CFD) methodology to simulate the hydrodynamics of horizontal-axis tidal current turbines (HATTs). First, an HATT blade was designed using the blade element momentum method in conjunction with a genetic optimization algorithm. Several unstructured computational grids were generated using this blade geometry and steady CFD simulations were used to perform a grid resolution study. Transient simulations were then performed to determine the effect of time-dependent flow phenomena and the size of the computational timestep on the numerical solution. Qualitative measures of the CFD solutions were independent of the grid resolution. Conversely, quantitative comparisons of the results indicated that the use of coarse computational grids results in an under prediction of the hydrodynamic forces on the turbine blade in comparison to the forces predicted using more resolved grids. For the turbine operating conditions considered in this study, the effect of the computational timestep on the CFD solution was found to be minimal, and the results from steady and transient simulations were in good agreement. Additionally, the CFD results were compared to corresponding blade element momentum method calculations and reasonable agreement was shown. Nevertheless, we expect that for other turbine operating conditions, where the flow over the blade is separated, transient simulations will be required.
Internal Waves Impact on the Sea Surface
Authors: Shugan Igor V. , Hwung Hwung-Hweng , Yang Ray-Yeng
Published: November 2011

The impact of subsurface currents induced by internal waves on nonlinear Stokes surface waves is theoretically analyzed. An analytical and numerical solution of the modulation equations are found under the conditions close to the group velocity resonance. It is shown that smoothing of the down current surface waves is accompanied by a relatively high-frequency modulation while the profile of the opposing current is reproduced by the surface wave’s envelope. The possibility of generation of an internal wave forerunner, that is a modulated surface wavepacket, is established. Long surface waves can form the wave modulation forerunner ahead of the internal wave, while the relatively short surface waves create the trace of the internal wave. Modulation of surface waves by the periodic internal wave train may have the characteristic period less than the internal wave period and be no uniform while crossing the current zone. Surface wave excitation by internal waves, observable at their group resonance is efficient only on the opposing current.
A Numerical Study on Squat of a Wigley Hull
Authors: Alidadi Mahmoud , Calisal Sander
Published: November 2011

A numerical study is conducted to calculate the squat for a wigley hull. An approach based on slender body theory is used to convert the three dimensional ship problem into a series of two dimensional problems in cross sections from bow to stern (solved sequentially in time). A boundary element method is used to compute the flow potential at every cross section. The ship squat is calculated from the pressure integration over the hull. Numerical results for the Wigley hull is presented and compared with the experimental results.
Measurements of Surface Waves Using Low-Grazing Angle High-Resolution Pulse-Doppler Radar
Authors: Hackett Erin E. , Fullerton Anne M. , Merrill Craig F. , Fu Thomas C.
Published: November 2011

Techniques for extracting surface wave characteristics from radar backscatter have been investigated and improved over the last several decades. Much of this research has focused on the use of backscatter intensity from navigational radars for characterization of wave period and direction, and has clearly demonstrated accurate measurement of these wave characteristics. However, the precise determination of significant wave height has been more problematic due to the required application of a modulation transfer function. Furthermore, low sea states generally do not provide enough backscatter intensity for evaluation of wave characteristics, and thus, navigational radar measurements are restricted to relatively high sea states. More recently, techniques using Doppler velocities as a measurement of surface waves have been an area of increasing focus and development. An advantage of this approach is that no modulation transfer function is required, and only phase information is used from the backscattered radar signal. Recent research suggests that the relationship between Doppler velocities and wave height may be more consistent than that between radar backscatter intensity and wave height. In July 2010, surface waves were measured during an experiment at the Scripps Institution of Oceanography pier. Radar measurements were performed using a high-resolution pulse-Doppler instrumentation radar at low grazing angle (∼1 deg) with a pulse repetition frequency of 800 Hz and spatial resolutions of 10–30 cm. Radar data for X- and Ku-bands using both VV and HH polarizations were collected. Concurrent buoy measurements were also performed, along with the collection of wind speed and direction data. Measured seaways consisted of small significant wave heights (glassy conditions to <1 m), and contained combinations of wind sea and swell. Doppler processing of the radar data provided estimates of surface wave orbital velocity spectra in wavenumber and frequency domains. The velocity spectra were converted to sea surface elevation spectra. Using these spectra, peak periods were computed as well as RMS wave heights, thus providing approximate significant wave heights. The methods for extracting wave spectra, peak periods, and significant wave heights are discussed, and results are compared with buoy measurements. When sufficient capillary waves existed on the sea surface, the radar and buoy measured wave spectra were in agreement, and analysis indicates that the instrumentation radar was able to detect and spectrally distinguish between wind seas and swell.
Space-Time Waves and Spectra in the Northern Adriatic Sea via a Wave Acquisition Stereo System
Authors: Fedele Francesco , Benetazzo Alvise , Forristall George Z.
Published: November 2011

A novel Wave Acquisition Stereo System (WASS) is proposed for the stereo reconstruction of oceanic waves both in space and time. To test the performance of such video observational technology, we have deployed WASS at the oceanographic tower Acqua Alta in the Northern Adriatic Sea, off the Venice coast in Italy. The analysis of WASS video measurements yielded accurate estimates of the oceanic sea state dynamics, the associated directional spectra and wave surface statistics that agree well with theoretical models. Further, the expected largest wave surface height over an area is estimated via both Piterbarg’s theory (Piterbarg 1995) and Adler’s Euler characteristics (Adler 1981, Adler and Taylor 2007). It is found that the largest surface height over the imaged area is considerably larger than the maximum crest observed in time at a single point, in agreement with theoretical predictions.
A Practical Method to Determine the Effect of Current on Wave Loads and Motions of Offshore Structures
Authors: Bunnik Tim
Published: November 2011

In this paper a linear diffraction method is presented which is able to determine accurately and fast the effect of current on motions of, and first- and second-order wave loads on offshore structures. The current flow is modeled by double-body potential flow, thereby neglecting viscous effects and stationary wave effects. The interaction between the double-body flow and the first-order non-stationary flow is modeled up to first order in the current speed, thereby restricting the method to small current speeds. A direct pressure integration method is used to evaluate the wave drift forces. Therefore, the gradient of the double-body velocities is required, which is evaluated using an additional boundary integral. The interaction between the double-body flow and the non-stationary flow leads to a modified free-surface condition which is satisfied using panels on the free surface. On these panels pulsating sources are placed satisfying the zero-speed free surface condition in the frequency domain. The method is validated against results published by Zhao and Faltinsen for a fixed vertical truncated cylinder. Furthermore, experimental data for a tanker, published by Wichers, [11] is used to validate the method for realistic ship shapes. In both cases a good agreement is obtained.
Numerical Studies of Installation and Extraction Processes of Jack-Up Ships
Authors: Qiu Gang , Grabe Ju¨rgen , Kukolka Nikolai , Vollstedt Hans-Werner
Published: November 2011

New Jack-up ships are built to transport offshore wind turbines from harbor and assemble them with the help of cranes on the ship at the site of installation. Every ship has four stilts, which can be lowered to seabed and jack the ship up. However, penetration and extraction the stilts at the harbor area could jeopardize the existing quay wall construction. In this paper two conceptual designs of foundations, which are used to improve the strength of the seabed in front of the quay wall, are investigated using numerical methods. Through soil exchange in open-ended cylinder or bucket foundation the strength of the seabed should be improved so that jack-up ships can dock directly at the quay wall and lower the stilts into the foundations. Three dimensional finite element analysis using a coupled Eulerian-Lagrangian method (CEL) are carried out to simulate penetration and extraction process. A hypoplastic constitutive model and the Mohr-Coulomb constitutive model are used to describe the filling. The studies of influences of geometry of foundations as well as the soil parameters on the bearing capacity of stilts and failure mechanism in foundations are carried out as the design basis of the foundations.
Parametric Study on the Axial Vibrations of Riser Suspended and Moored by Chains (RSAA) Configurations
Authors: Dantas Claudio Marcio Silva , de Siqueira Marcos Queija , da Silva Pereira Victor Milanez , de Sousa Fernando Jorge Mendes , Ellwanger Gilberto Bruno , Masetti Isai´as Quaresma
Published: November 2011

Recently, in order to minimize the influence of the vertical motions in the risers and consequently allow the utilization of FPSOs in deep waters, a new riser configuration called RSAA (riser suspended and moored by chains - in Portuguese), composed of a rigid vertical riser, flexible structures and mooring line segments (top and bottom) was proposed. This configuration presents solutions to the most critical points in a riser design: the top tensions are dissociated from the bending moments at the top region, and the curvatures at the TDP are reduced by utilization of floaters. Feasibility analyses have shown that the vertical riser is the most critical part of the proposed system due to the FPSO high level of vertical motions. These motions are transmitted by the top chains, leading to high levels of axial stress variation due to dynamic tension. Faced with this, a parametric study is vital in order to understand the system’s behavior as well as to establish the main parameters which influence its structural behavior. Analytical methods may require some slight simplifications of the problem to be applicable, but they generally lead to compact formulas that do explain which parameters influence the results and why and how it does so. This work proposes an analytical model to determine axial stress and tension variations at the vertical riser, considering some simplifying hypotheses, like the flexible structures and mooring line segments at the bottom will be replaced by a mass and a spring. Neglecting some nonlinearities but considering the coupling between axial and transversal vibrations, a random dynamic analysis in the frequency domain can be performed to evaluate the maximum stresses and tensions levels with considerably lower computational costs.
Fatigue Life Extension of Offshore Structures by Ultrasonic Peening
Authors: Lopez Martinez Luis
Published: November 2011

The service life of offshore installations is limited by its structural integrity. Furthermore the structural integrity is mainly governed by the fatigue resistance of critical welded details. In a FPSO installation these details are among others pallet stools weld joints to deck structure and bulkheads/web frames weld connections to longitudinal in ballast tanks. ultrasonic peening can improve the fatigue resistance of welded joints. Fatigue test results shows an increase of four times for high stress ranges and up to ten times for high cycle fatigue. For specimens which have already consumed half of their fatigue life the treatment resets the clock to zero, as a minimum value. Consequently ultrasonic peening treatment was applied to several offshore installations on fatigue sensitive weld connections with the objective to extend the service life of the these. Finite Element Analysis carried out by classification societies for these offshore structures demonstrated critical fatigue lives for several weld connections. These weld connections were then treated by ultrasonic peening with the objective to extend their fatigue lives and by doing that reach the targeted service life for the installation. The successful application of the ultrasonic peening treatment was a pioneering work which involved several partners. A pilot project on a FPSO started in 2005 and the treated critical weld connections are still intact and show not sign of crack initiation despite the fact the calculations then showed shorter fatigue lives than the life span already consumed. As a result the same ultrasonic peening procedure has been proposed to be applied for other fatigue sensitive locations on the installation. Offshore installations around the world are reaching their original design life. Most of the operators chose to extend the service life of their assets rather than scrape them and build new. The reasons for that are: improved oil recovering techniques, time required to get a new build installation on site, environment concerns, wiser management of energy and resources among others. Therefore the Life Extension of Offshore Installations is a subject of current interest for the upstream industry.
The Interaction of Tsunamis With Ocean Swell: An Experimental Study
Authors: Kaihatu James M. , El Safty Hoda M.
Published: November 2011

Our objective is to investigate the effect of combined swell–tsunami interaction on the nature of the tsunami — in particular the surface elevation, the runup speed and the near-bottom velocities. Laboratory testing in the Tsunami Wave Basin at Oregon State University has been performed to simulate this interaction, with free surface elevations and near-bottom velocities measured at various locations over a plane sloping beach. Random wavetrains with varying initial mean steepness were generated in concert with the tsunami. Preliminary analysis of the data reveals that high steepness ocean swell changes the spectral signature of the tsunami, particularly at high frequencies. There is also a significant difference in location of the breakpoint of the tsunami with overriding swell.
Pipeline Shore Approach Design: Case Study
Authors: McMaster Scott Y. , Campbell Dean R. , Jas Eric
Published: November 2011

An insight is provided into the design of a large diameter high pressure gas pipeline shore approach for an LNG project off the coast of North Western Australia. The shore approach is located in a challenging and congested area, within one of Australia’s busiest ports. In close proximity to the pipeline route are two existing high pressure gas pipelines, several major shipping channels, a large spoil ground and environmentally sensitive coral reefs. Throughout the design process, careful consideration has been given to environmental and heritage constraints. In the case of the pipeline shore approach, prevention of coral mortality due to dredging induced turbidity has been a key priority. Ensuring the preservation of the heritage site adjacent to the landfall site has also been a major consideration. This paper describes the numerous challenges faced in designing the pipeline shore approach. A description of the design processes used to develop the secondary stabilisation and accidental external impact designs is provided. The unique methods employed to install the trunkline system across an operating shipping channel are also described. The information provided in this paper can be applied to the design and development of numerous pipeline shore approaches in the future. Individuals interested in pipeline secondary stabilisation, impact protection, shore crossings and pipelay techniques will also find this paper of value. This paper contributes to the technical knowledge base of the offshore industry by displaying the benefits of effectively combining relevant theoretical approaches with state of the art physical model testing methods and best practice installation techniques. This work demonstrates how innovative design practices can be successfully applied to produce a safe, cost effective and robust pipeline shore approach design in a challenging area.
Experimental Set-Up for Analysis of Subsea Equipment Installation
Authors: de Mello Pedro C. , Rateiro Felipe , Fujarra Andre´ L. C. , Oshiro Anderson T. , Neves Cassiano R. , dos Santos Melquisedec F. , Tannuri Eduardo A.
Published: November 2011

This paper and the companion paper (Rateiro et al., 2011) present an illustrative case of the joint application of experimental tests and numerical simulations for the proper analysis of a complex offshore operation (launching of a sub-sea equipment using one or two vessels). The main idea of the whole study is to compare two methodologies and operational procedures for the installation of the equipment in the seabed, using either one vessel (conventional operation) or two vessels in a synchronized operation in a Y-configuration. The experiment was conducted under a simplified configuration, and uses ODF (one degree of freedom) servo-actuator to emulate the vessels induced motion. The hydrodynamic properties of the equipment was then calculated, and some preliminary conclusions about system dynamics could also be drawn. After that, numerical simulations were conducted, considering the coupled dynamics of the vessels, cables and equipments under irregular sea state. Those simulations were used for determining the limiting environmental condition for a safe operation, and are described in the companion paper. This paper describes the reduced scale experimental setup used for evaluating the hydrodynamic properties of the equipment during a subsea installation under waves excitation. The reduced scale model of the equipment was attached to one or two servo-actuator, that emulate the wave-induced motion. The tests were conducted at the physical wave basin of Numerical Offshore Tank (Tanque de Provas Nume´rico – TPN). The experiments enabled the preliminary evaluation of the dynamic behavior of the equipment when submerged by one or two launching cables. In the later case (two launching cables), several tests considering phase shifts between the servo-actuator have been conducted. The reduction in the dynamic amplification of cable traction could also be experimentally verified.
Global Buckling of Pipe-in-Pipe: Structural Response and Design Criteria
Authors: Goplen Stig , Fyrileiv Olav , Grandal Jon Petter , Bo̸rsheim Lars
Published: November 2011

Pipe-in-pipe is a flowline concept that shows an increasing popularity when certain flow assurance aspects are to be dealt with. U-values in the order of 1W/m2K are achievable, ensuring that the well fluid temperature can be kept high for longer time after shut-down and over longer distances. This two layer steel construction also has some mechanical properties that can be beneficial for the design such as a stronger, more robust cross section, better protection against 3rd party interference and increased stability as a few examples. Disadvantages such as high weight causing higher bending moments during installation or in free spans should also be mentioned. The global response of a pipe-in-pipe will be very much similar to a conventional single pipeline. It will expand due to pressure and temperature loads, longitudinally or in combination with lateral motion (global buckling), always in the direction of the lowest resistance. However, there are also some important differences compared with conventional pipelines. Interaction between the inner and outer pipeline is secured using rigid bulk heads at each end. Along the pipeline the separation of the two pipes can be ensured by e.g. rollers, plates, spacers, insulation and additional intermittent bulk heads. In the most extreme case the spacing between intermittent buck heads is down to every pipe joint. At present there is no public pipeline code that in detail addresses pipe-in-pipe. One reason is of course that there is not only one pipe-in-pipe concept but a large number of variants. This paper’s focus is on mechanical behaviour of a pipe-in-pipe in relation to expansion and global buckling. Both the friction between to two pipes and soil friction influence on the global buckling pattern is discussed. An introduction is given to where pressure and temperature loads are acting and how these loads raises forces in the pipeline (load effects).
Concept of Seafloor Mineral Processing for Development of Seafloor Massive Sulfides
Authors: Nakajima Yasuharu , Uto Shotaro , Kanada Shigeo , Yamamoto Joji , Takahashi Ichihiko , Otabe Sho , Sadaki Jun , Okaya Katsunori , Matsuo Seiji , Fujita Toyohisa
Published: November 2011

Seafloor Massive Sulfides (SMS), which were formed by deposition of precipitates from hydrothermal fluids vented from seafloor, is one of unconventional mineral resources beneath deep seafloors in the world. The authors have proposed the concept of seafloor mineral processing for development of SMS, where useful minerals included in SMS ores are separated on seafloor to be lifted while the remaining gangue is disposed on seafloor in appropriate ways. To apply column flotation, one of conventional methods in mineral processing, to seafloor mineral processing, the authors carried out simulating experiments of column flotation on deep seafloor using ores including copper, iron, lead and zinc as metallic elements. Prior to the experiments at high pressures, preparatory experiments at the atmospheric pressure were carried out to find out the optimum condition of the properties of pulp, a mixture of feed ore, water and chemical reagents. In flotation experiments at high pressures, formation and overflow of froth layer by bubbling were observed at 1MPa in both of pulps with pure water and artificial seawater. The analytical data showed that the concentration of metallic elements such as copper and zinc in the concentrates recovered from the experiments was higher than that in the feed ores while the concentration of silicon and calcium, which are assigned to gangue, in the concentrates was lower than that in the feed ores. These results suggest that column flotation can be applied to operation on seafloor.
WINDOPT: An Optimization Tool for Floating Support Structures for Deep Water Wind Turbines
Authors: Fylling Ivar , Berthelsen Petter Andreas
Published: November 2011

An integrated design tool for optimization of a floating wind turbine support structure of the spar buoy type, including mooring system and power takeoff cable, is described in this paper. The program utilizes efficient design tools for analysis of mooring system forces and vessel motions, and combines this with a gradient method for solution of non-linear optimization problems with arbitrary constraints. The objective function to be minimized is the spar buoy cost, and the mooring line and cable costs. Typical design requirements that may be included as constraints are: mooring line load limitations and minimum fatigue life, cable curvature radius, cable tension, tower top acceleration, and vessel motion and inclination. The spar buoy is modelled as composed of a set of cylindrical sections with different mass, buoyancy and cost properties, where each section is assumed to have a uniform mass distribution. It is assumed that a representative initial cost figure is available, and that it can be scaled in proportion with material mass. A simple relationship between mass and geometrical properties is proposed for both massive and thin walled tubular sections. Examples are included to demonstrate the various aspects of the optimization approach, including different parameterizations of the spar buoy.
Characteristics of the Environment Around a Massive Sea-Floor Sulfide Area in the Okinawa Trough
Authors: Ishida Hiroshi , Maeda Nobuhiro , Miwa Tetsuya , Yamazaki Tetsuo , Shirayama Yoshihisa , Toyohara Tetsuhiko , Okamoto Nobuyuki , Kodama Takayoshi
Published: November 2011

It is necessary to carry out a proper environmental impact assessment for not only the sea-floor massive sulfide area where a special hydrothermal-vent chemosynthetic ecosystem is observed, but also its surrounding area. This paper shows provisional results of the environmental baseline survey conducted at the Izena Cauldron in 2009. Environmental conditions differed clearly between inside and outside of the Cauldron. In the inside area, a high turbidity layer was recognized at ca. 200 m above the sea-floor. In the bottom layer close to the hydrothermal active region, water temperature was slightly higher than the surrounding area with the lower pH, higher concentrations of both carbon dioxide and the dissolved Mn. Inside the Cauldron, the sulfur isotope ratio of the sediment close to a sea-floor massive sulfide was similar to that of the hydrothermal sulfate. In addition, heavy metal concentrations of the sediment were higher inside than outside of the Cauldron. Especially, concentrations of Cd, As and Hg were as high as poisonous levels. These results show the possibility that most of the chemical materials derived from hydrothermal vent remain in the Cauldron. Pelagic shrimps of the family Oplophoridae were widely distributed in the bottom layer inside the Cauldron. The biomass of benthic shrimps which belong to infraorder Caridea was higher inside than outside of the Cauldron. These higher biomass was likely caused by the abundant organic matter. This hypothesis was reinforced by the result of the mooring sediment trap (placed at ca. 50 m above the seafloor) experiment, which demonstrated that the settling particle in the Cauldron was supplied from not only the euphotic zone but also the hydrothermal-vent ecosystem.
Efficiency and Optimal Loading of Contra-Rotating Marine Turbines
Authors: Xu Wei , Kinnas Spyros A.
Published: November 2011

In this paper, an optimization method is developed for determining the loading on each component, which leads to the maximum efficiency (i.e. maximum output power) of a contra-rotating turbine when subject to uniform inflow. The lifting line model is adopted and both the self-induced velocities and the interaction induced velocities between the front and the back components are included. The optimum ratio of rotational velocities for reducing the torque on support structures and the performance effects of the gap distance between two components are investigated. The optimum distance for two in-line turbines in a turbine farm is also analyzed.
Numerical and Experimental Tools for Offshore DP Operations
Authors: Rampazzo Fabiano P. , Silva Joa˜o Luis B. , Vieira Daniel P. , Pacifico Antonio L. , Moratelli Junior Lazaro , Tannuri Eduardo A.
Published: November 2011

DP crane vessel operation can be analyzed based on the uncoupled system or considering the fully coupled system. Parameters such as top-crane acceleration, thruster capability and vessel motions are evaluated for several environmental conditions. Numerical and experimental tools are used and the important result of this analysis is the maximum condition in such that the operation can be safely executed. Those operations are critical, since the vessel is kept in close proximity with other unit and large loads are transported in a pendulum configuration. A precise positioning of the crane-vessel is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The uncoupled analysis approach does not consider the influence of the other unit in the crane vessel. This paper presents a methodology for evaluating a DP crane vessel in the offshore operations (DP crane vessel, load being transported, mooring and assistance lines, platform) considering the fully coupled method based on integration of the in house codes with the commercial code WAMIT® system. The methodology is based on the integration of numerical and experimental tools. The dimensions of the transported modules and the proximity of the vessels change the behavior of the vessel motions and line tensions. So, a full nonlinear time domain simulator (TPN – Numerical Offshore Tank) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load and the hydrodynamic interference between the bodies. In order to calibrate the numerical model, several experimental tests are performed such as wind tests with some positions of the crane, tests in towing tanks to evaluated the current effects, thrusters tests to calibrate DP algorithm and wave test with the two bodies. In some cases a complementary CFD analysis is requested in order to evaluate the current and wind shadow effect. Several alternative relative positions between the vessels can be evaluated. This methodology results a more accurate estimative of the system performance.
SPH Simulation of Hydrodynamic Forces on Subsea Pipelines
Authors: Abdolmaleki Kourosh
Published: November 2011

Hydrodynamic forces on subsea pipelines are simulated using Smoothed Particle Hydrodynamics (SPH) method. The objective is to assess the suitability of this method for common sub-sea engineering problems. The standard SPH formulation is used for simulation of cases with high KC and Re numbers, where the flow becomes turbulent with laminar or partially turbulent boundary layer. The numerical model includes a pipe section with smooth surface resting on a flat bottom. The pipe is exposed to various combinations of regular waves and current. The current is modelled as a steady flow of fluid particles and the waves are represented by forced oscillations of the pipe at defined frequencies and amplitudes. The selected KC and Re numbers produces subcritical and supercritical flows, which simulate extreme load cases on pipelines. In subcritical flows, the estimated forces on the pipeline agree well with experimental data. In supercritical flows with high KC and Re values, a relatively finer particle resolution is required in order to capture multiple harmonics of oscillating lift force. In conclusion, the SPH method could satisfactorily predict hydrodynamic forces on pipelines for the cases investigated.
Vibration Reduction in Steel Catenary Risers by the Use of Viscoelastic Materials
Authors: Borges Fla´via , Roitman Ney , Magluta Carlos , Castello Daniel A. , Franciss Ricardo
Published: November 2011

The increasing need for petroleum is leading to an exploration in waters each time deeper, leading the structures to have a complex behavior. One of the main components in this area are the risers. These structures are submitted to dynamic loads, among them, it can stand out the one that it is induced by the detachment of vortexes when the structure is submitted to sea currents. These loads may reduce their lifetime due to fatigue. Therefore, many methodologies are being developed to increase the damping of the risers and reduce the vibration effects. One of the ways to reduce the vibrations is the use of viscoelastic materials associated with constraining layers, known in literature as “sandwich structures”. One possible application for this concept is related to the control and the reduction of vibrations in steel catenary risers. The main purpose of this work is present a methodology in order to increase the structural damping factors using the concept of sandwich structures with viscoelastic materials. This application differs from the usual because offshore structures work in lower frequencies than the civil ones, leading the need of an own development for its application. It was developed a numerical model of the sandwich tubes, and its results are evaluated through experimental tests in simple structures accomplished at the Structures Laboratory at COPPE/UFRJ. Through this analysis it is observed a great addition of damping that would allow a reduction of the vibration levels and an increase of the structures lifetime, for example, in steel catenary risers.
Flow-Induced Vibrations of Subsea Jumpers due to Internal Multi-Phase Flow
Authors: Pontaza Juan P. , Menon Raghu G.
Published: November 2011

Subsea jumpers are steel pipe sections that connect hardware components on the seafloor (e.g. trees, manifolds, and sleds) and typically operate in multi-phase flow. They are designed with bends to accommodate limited expansion due to variations in temperature and pressure. Under certain conditions significant fluctuating forces can be induced in flow-turning elements like bends and tees. These fluctuating forces may cause severe piping vibrations and weld fatigue damage. This paper presents a flow-induced vibration screening procedure based on the 3-D numerical simulation of unsteady internal multi-phase flow in subsea well jumpers, the prediction of associated flow-induced forces in flow-turning elements, and the prediction of structural response, including fatigue life estimates. We consider a 6 inch (nominal) diameter well jumper with six turning elements (i.e. six blind Tees), having 70 feet of suspended span, and perform simulations for two different flow conditions representative of early- and mid-life production. We find that the dominant frequencies of flow-induced vibration are those associated with modes 1 through 4 and that stresses are highest in mid-life flow conditions when the gas volumetric void fraction is 55%.
Calculation of the Accelerated Breaking-Roller Propagation Speed and Wave Energy Transfer to the Roller
Authors: Okamoto Takashi , Fortes Conceic¸a˜o Juana
Published: November 2011

Wave breaking has different physics from the potential flow wave motion. The roller model introduced by Svendsen [1] illustrates the separation of the wave motion and the roller. The roller propagation speed, therefore, is a very important factor for the energy calculation of the bore. The wave celerity data collected at the wave tank displays that the maximum roller propagation speed occurs when the wave has already decayed due to the breaking. This fact clearly displays that the bore energy cannot be calculated only from the wave height as it is done for non-breaking waves. It is certain that most the energy is dissipated through the roller formation in the outer surfzone, but a certain amount of energy is transferred to the roller at the same time and it accelerates the bore speed. Slow decay of the roller propagation speed indicates that the excess energy left in the roller dissipates in the inner surfzone at much slower rate than in the outer surfzone. Therefore, these two zones have to be clearly separated, but the amount of energy transferred into the roller is unknown. In this paper, we focus on the examination of the peak roller propagation speed that appears at the border of the outer and the inner surfzone by using the experimental data collected at the wave tank. In that way, the initial condition of roller propagation speed can be determined for the inner surfzone. The energy conservation between the wave motion and the roller kinetic energy derives an equation to calculate the roller propagation speed. The energy transfer rate is estimated by adjusting the value given by the full energy conversion with the observed roller propagation speed. It is found that about half of the energy is transferred into the roller. The model successfully illustrates the peak bore propagation speed which existing formulae cannot explain.
A User Evaluation Study on the Universal Network of the Water Transportation in the Seto Inland Sea in Japan
Authors: Sugahara Masashi , Noto Keichi , Idoji Atsushi , Yamamoto Kazukiyo , Hanai Kenta , Kondo Takeo
Published: November 2011

As Japan has increasingly becoming a so-called “super-aging society,” and the number of people with mobility impairment has increased, the barrier-free improvements have been implemented to public facilities so far. After the New Barrier-free Law has been enforced, however, the conceptual basis of such improvements has been shifting toward the universal design, based on the idea that everybody should be able to use facilities impartially. This study clarifies the present situation and problems of the barrier-free improvements from a passenger ship terminal to the inside of a ship, and elucidates improvement issues of nodal points of future marine and land transport. We carried out a questionnaire and site survey for the Hiroshima Port Ujina Passenger Boat Terminal, as well as the ships used, where the improvements are made based on the New Barrier-free Law.
Estimation of Tropical Cyclone Heat Potential From Oceanic Measurements
Authors: Ho Chung-Ru , Tsao Yen-Hsuan , Kuo Nan-Jung , Huang Shih-Jen
Published: November 2011

The primary purpose of this study is to estimate the tropical cyclone heat potential (TCHP) in the western North Pacific Ocean using in-situ measurements and satellite remote sensing data, as well as to explore the influence of TCHP on the genesis and intensification of typhoon in this region. The TCHP is defined as the integration of heat content from the depth of 26°C isotherm to the sea surface. Sea surface height and sea surface temperature data are used to estimate the TCHP based on a two-layer reduced gravity model. Totally 35 typhoons from 2006 to 2009 are analyzed in this study. The result shows that the typhoon is dramatically developed when it goes through the area with more TCHP than surroundings. From the result of regression analysis, the correlation coefficient between typhoon intensity and accumulated TCHP is above 0.8. It implies that the typhoon intensity changes might be controlled by the TCHP conditions of tropical cyclone formation region.
Global Analysis of a Floating Wind Turbine Using an Aero-Hydro-Elastic Numerical Model: Part 2—Benchmark Study
Authors: Luxcey Neil , Ormberg Harald , Passano Elizabeth
Published: November 2011

This paper describes and presents the results of a benchmark study of a floating wind turbine numerical model that includes aero- and hydro-elasticity. The modelled wind turbine is the NREL offshore 5 MW baseline wind turbine whose specifications are publicly available. The first part of this paper demonstrates the importance of including aeroelasticity and hydroelasticity in the system. Power production, internal forces and motion amplitudes are compared to results from models using a rigid tower and rigid blades. Comparisons are performed for different weather conditions such as calm water, regular and irregular waves, constant and varying wind. The consequences of including elasticity in the different parts of the model are studied. The second part of the paper presents a benchmark study against the codes of the Offshore Code Comparison Collaboration. The floater motions, blade and tower deflection and power generation are presented and discussed.
Scientific Drilling Program of Drilling Vessel Chikyu and Drilling Data Acquisition for Future Technical Development
Authors: Inoue Tomoya , Wada Kazuyasu , Miyazaki Eigo , Miyazaki Tsuyoshi
Published: November 2011

The scientific drilling vessel Chikyu has started drilling at Nankai trough under the international organization, IODP. The Nankai trough located beneath the ocean off the southwest coast of Japan is one of the most active earthquake zones on the planet and one of the best-studied subduction zones as well. The Nankai Trough Seismogenic Zone Experiment attempts for the first time to drill, sample, and instrument the earthquake-causing or the seismogenic portion of Earth’s crust, where violent, large-scale earthquakes have occurred repeatedly throughout history. Before starting the international drilling operations, an integration drilling test off Shimokita Peninsula was conducted and we acquired actual drilling data such as vessel heave, hook load, and compensator position. Confirming its validity, data acquisition systems have worked continuously in international drilling operations. It is very important to consider the actual drilling data for the drilling operation and for further technical development. This paper describes the scientific drilling programs of the drilling vessel Chikyu and the drilling data acquisition for future technical development in relation with the sample data acquired in the internal drilling operations.
Wave Statistics in Nonlinear Sea States
Authors: Latheef Mohamed , Swan Chris
Published: November 2011

This paper concerns the statistical distribution of both wave crest elevations and wave heights in deep water. A new set of laboratory observations undertaken in a directional wave basin located in the Hydrodynamics laboratory in the Department of Civil and Environmental Engineering at Imperial College London is presented. The resulting data were analysed and compared to a number of commonly applied statistical distributions. In respect of the wave crest elevations the measured data is compared to both linear and second-order order distributions, whilst the wave heights were compared to the Rayleigh distribution, the Forristall (1978) [1] empirical distribution and the modified Glukhovskiy distribution ([2] and [3]). Taken as a whole, the data confirms that the directionality of the sea state is critically important in determining the statistical distributions. For example, in terms of the wave crest statistics effects beyond second-order are most pronounced in uni-directional seas. However, if the sea state is sufficiently steep, nonlinear effects arising at third order and above can also be significant in directionally spread seas. Important departures from Forristall’s empirical distribution for the wave heights are also identified. In particular, the data highlights the limiting effect of wave breaking in the most severe seas suggesting that many of the commonly applied design solutions may be conservative in terms of crest height and wave height predictions corresponding to a small (10−4) probability of exceedance.