bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Multi-Connected Floating Body System
Authors: Ikegami Kunihiro , Matsuura Masami , Hayashi Noriyuki , Tanigaki Shinkichi , Kawazoe Tsuyoshi , Yamauchi Yoshihisa , Toshimitsu Kazuki , Nagaosa Satoshi
Published: November 2008

A multi-connected floating body system composed of many connected small-scale floating body units has a number of advantages with regard to construction and performance. To realize the multi-connected floating body system, a new type of mechanical connecting device was developed. It is composed of multi-degrees of freedom connecting mechanism and restricting mechanism to control a restricting condition between floating body units, and its effectiveness was confirmed by model basin test in waves. Next, friction and wear tests in the seawater environment led to the discovery of suitable materials for oscillatory sliding parts in multi-degrees of freedom connecting mechanism. Finally, a field test performed for two floating body units connected by use of the mechanical connecting device proved that the developed mechanical connecting device was of practical use.
Development of a Decommissioning Cost Model for Australian Offshore Platforms
Authors: O’Neill Lee , Cole Geoff , Ronalds Beverley
Published: November 2008

Experience has shown that regional factors can contribute to significant variability in decommissioning costs for offshore platforms. Nevertheless, previous studies aimed at estimating decommissioning costs have been valuable inputs for operators, regulators and decommissioning contractors as they develop abandonment and decommissioning strategies and public policy. Estimated costs associated with decommissioning offshore oil and gas platforms in Australia have not been reported widely in the open literature. This paper summarises the physical and regulatory environment in Australia, and develops a cost model which reflects the decommissioning challenges for fixed platforms in this remote region. This cost model could be readily applied to other remote petroleum provinces provided that mobilization times and the nature of the local ocean environment are known. The total cost of decommissioning all 39 current fixed platforms in Australian waters is estimated to be between US$845 and US$1044 million.
Greatly Extended Distance Pipeline Monitoring Using Fibre Optics
Authors: Nikles M. , Briffod F. , Burke R. , Lyons G.
Published: November 2008

Monitoring of the effects of hydrocarbon pipeline blockages such as may be caused by hydrates and waxes is receiving a higher level of consideration as the distributed sensing capability offered by the use of fibre optic technology matures. The extent of the hydrate or wax formation problem increases with pipeline length through the effects of cooling. The challenge is significantly greater when assuring flows in deep water and remote subsea locations. Commercially available strain and temperature sensing equipment such as discrete FBGs (Fibre Bragg Gratings) and fully distributed sensing techniques such as Raman DTS (distributed temperature sensor) and Brillouin OTDR (optical time domain reflectometry) typically offer sensing lengths of the order of 20–30km. Whilst this is in many instances a useful length, it is not sufficient to be able to monitor the whole of a pipeline which may be several hundreds of kilometres in length. The authors have developed and demonstrated a method for extending the reach of a Brillouin OTDR interrogating system such that sensing sections of conventional length (approximately 25km) can be successfully interrogated from distances well in excess of 100km without having to compromise on the performance. With a single instrument, more than 250km of sensing fibre can be monitored to within 1.5 metre resolution. By this means, temperature and strain profiles may be measured for the entire pipeline length which will enable active flow assurance measures to be taken including identifying the presence, nature and extent of blockages as they form. Consequently, any corrective action taken by the pipeline operators will be on an informed basis (such as the injection of an optimised quantity of inhibitor), and will incur a significantly lower level of risk than is currently possible. This paper describes the technology which has been developed to meet this requirement and provides results of simulated pipeline blockage effects which demonstrate this.
Hydrodynamic Loads on Twisted Ropes and Hawsers
Authors: Winkel Hans-Joachim , Paschen Mathias
Published: November 2008

The loads on both a model of a smooth cable and a helical strake (also known as scrouton spiral) were measured in a wind tunnel. The coefficients of drag, lift and transverse force were ascertained for an angle of attack between 0 and 360 degrees. Results show that the drag coefficient increases by the spiral in each case whereas the lift coefficient changes only insignificantly. A defined transverse force is caused by the spiral. To find an explanation of this force by the circulation a simple mathematical model is given. Finally the behaviour of a twisted rope in water calculated by a known code is predicted in case of steady current.
A Novel Structural Joint With the Potential of Fire-Tolerance Improvement
Authors: Khonsari S. V. , England G. L. , Jamshidi-Vismeh A. R. , Fattahian N.
Published: November 2008

A new innovative ‘universal’ structural joint with multiple applications was devised. The two major conceived contexts for the use of this joint are ‘joining beams to columns,’ and ‘joining diagonal braces to horizontal ones.’ The main features of this joint are its high rotational capacity, its high shear deformation capacity, its high energy-dissipation capacity, its ability to contain damage, and its repalceability. Due to its geometry, it can well lend itself to protection measures against fire, normally practiced by the involving industries. This makes it a good candidate for being used in structures related to oil and gas industry, offshore or onshore. Through numerical modelling of the joint, also using mechanical properties of ‘mild steel,’ one of the best potential materials for the fabrication of the joint, at elevated temperatures, the ‘bending behaviour’ of the joint at various temperatures was studied. Additionally, the effects of using various thermal insulating materials, used for covering the joint, in reducing the temperature of various parts of the joint were investigated. Though not supported by any experiments, all these numerical analyses showed the potential of this joint for presenting improved behaviour during a fire scenario, as a result of using some insulating agents.
Research on a Fitting Structure of CFRP Riser Pipe
Authors: Watanabe Yoshiyasu , Ando Hirotomo , Suzuki Hideyuki , Inazaki Youichi
Published: November 2008

A deep-sea riser drilling vessel is now under construction in Japan for the purpose of scientific drilling. The target water depth of the vessel is 2500m for the time being and will be extended to 4000m in future. In the field of offshore oil drilling, the riser drilling has been practiced for many years and in recent years it is confirmed that the target water depth of 3000m with using steel riser pipes will be possible. However, the drilling up to the water depth of 4000m has not been experienced at all and will have a lot of technical issues. One of the most important issues is to make the weight of the riser pipe lighter and its axial rigidity higher. The purpose of this research is to make clear the design concept of the CFRP riser pipe that has multiple traplock structure and develop a CFRP riser pipe capable of drilling in 4000m deep waters. Here, referring to a series of research results on the leg fixing device for jackup rigs where similar fitting structure is adopted, a prototype of CFRP riser pipe which has multiple traplock structure is designed and five experimental models are fabricated and tested. Resulting from the comparison of the experimental results with those of finite element analysis, the findings have been obtained and it has been confirmed that it will be possible to develop an actual CFRP riser pipe that has enough strength for 4000 m water depth.
A Prototype Tool for Analysis and Design of Floating Fish Cages
Authors: Thomassen Paul E. , Leira Bernt J.
Published: November 2008

Floating fish cages are the main means of production in the multi billion euro salmon farming industry. Despite its pivotal role in production safety, protection of values, as well as in protection of the environment, neither verified structural design procedures nor computer tools for structural analysis and design have received much attention. To a large extent they can be regarded as not being in accordance with the current state-of-the-art of structural analysis and design of slender marine structures. A momentum to move towards a more scientific based design approach has been created by the requirements of the recently introduced Norwegian certification criteria and the accompanying design code NS 9415. A prototype for analysis and design of floating fish cages has been developed and is described herein. The tool is based on an object-oriented framework for general FE analysis. The framework has among other things been developed with ease of extensibility for the software developer in mind. The prototype is thus intended for iterative extension of the functionality. In the first development iteration, described here, the FE framework has been extended, with hydrodynamic load models and a user interface for analysis of floating fish farms. The development of the prototype shows that by building on an object oriented FE framework, specialized and focused applications for aquaculture can be developed with limited effort. As an example analysis — and a possible benchmark — a simplistic model of a steel frame is chosen. Comparison of results obtained with different load formulations indicated that the buoyancy load was more important than the hydrodynamic load.
A Direct Drive Wave Energy Converter: Simulations and Experiments
Authors: Danielsson O. , Leijon M. , Thorburn K. , Eriksson M. , Bernhoff H.
Published: November 2008

A novel wave energy converter concept is developed at Uppsala University, Department of Engineering Science. The concept is based on a synchronous permanent magnet linear generator, placed on the seabed. The piston of the generator is directly connected to a surface-floating buoy with a rope. The tension in the rope is maintained with springs that pull the piston downward. The three-phase current induced in the stator coil has a varying amplitude and frequency and a conversion is therefore necessary. Research has been carried out in three main areas: generator design, dynamic behavior and grid connection. The generator is modeled by full physics numeric simulations, based on a 2-dimensional finite element formulation of the time dependent electromagnetic field. A first set up is built to experimentally verify the simulated results. The impact of different parameters are estimated with mathematical models and verified by experiments. This paper includes both simulated and experimental results.
Advances in Frequency and Time Domain Coupled Analysis for Floating Production and Offloading Systems
Authors: Lang Donogh W. , Connolly Aengus , Lane Michael , Connaire Adrian D.
Published: November 2008

With the move to the development of remote, deepwater fields, increasing use is being made of floating production, storage and offloading (FPSO) facilities from which oil is intermittently offloaded to a shuttle tanker via offloading lines and an anchor leg mooring buoy. The response of the individual components of these systems is significantly influenced by hydrodynamic and mechanical coupling between adjacent components, precluding the use of traditional analysis techniques such as displacement RAOs derived from tank model tests or diffraction/radiation analyses of the independent components. Consequently, the reliable and accurate design of these complex systems requires an analysis tool capable of determining the fully coupled response of each of the individual components of the system. A recently-developed time domain coupled analysis tool has been extended to incorporate a frequency domain coupled analysis capability. This tool combines radiation/diffraction theory with a non-linear finite element (FE) structural analysis technique used for the analysis of slender offshore structures. This paper describes the application of frequency domain analysis to the coupled FE/floating structure problem, with particular consideration given to the linearisation of viscous drag loads on floating structures and the treatment of low-frequency second-order loads in the frequency domain. Results from frequency domain and time domain coupled analyses of a typical West of Africa type offloading system are compared, highlighting areas of application where frequency domain coupled analysis can offer significant benefits when used in conjunction with time domain analysis. Based on this, recommendations are made for the appropriate use of frequency and time domain coupled analysis for this type of system.
Final Design and Installation Constraints of a Shallow Water Oil Pipeline at the Capixaba North Terminal Offshore Brazil
Authors: de Azevedo Fa´bio Braga , Solano Rafael Familiar , de Freitas Hallai Julian , Bomfimsilva Carlos Terencio
Published: November 2008

The Petrobras Capixaba North Terminal - TNC is located in the state of Espirito Santo, in Brazil and is being built to receive the heavy and high viscosity oil produced onshore in the Fazenda Alegre field. This oil shall be heated prior to be pumped into the pipelines and it will be exported through a monobuoy and a tanker system. The two export pipelines are being laid to connect the onshore Terminal to a subsea PLEM to be installed under the monobuoy. The pipelines and PLEM were designed to operate with oil containing H2S in cyclic high temperature. This paper addresses the special concerns defined by the design activity to cope with the TNC operation conditions. It also focuses the modifications imposed to the installation process to fulfill the design and operation requirements.
Remote Connection and Disconnection Device for Mooring Lines KSDIN32, KS40 and KS50 Hook and Its Modelling for Structural Finite Elements
Authors: Lima de Almeida Jose Carlos , Sobral Ricardo
Published: November 2008

With the new sceneries of oil exploration in ultra deep waters that move forward to 3000 m, it has been putting for the companies that accepted this technological challenge significant border of the techno-scientific knowledge. Therefore, in this cases of ultra deep waters, where the use of the polyester synthetic rope in the Petrobras Floating Production Units, is present, it can appears the need replace. THE NEED TO LOOK FOR A SOLUTION FOR THE RELATIVE PROBLEMS THE CHANGES OF THE POLYESTER ROPE IN THE PRODUCTION PLATFORMS WITHOUT THE CHANGE OF THE EXTENSION OF BOTTOM AND OF ITS FUNDATION (FIXED POINT). THEREFORE, APPEARS THE KS HOOK AND ITS OTIMIZATION UNDER THE OPTICS OF THE CONCEPTS OF THE MECHANICS OF THE FRACTURE AND OF THE TOOLS EXISTENT COMPUTACIONAIS (MEF AND MOORING SOFTWARE). This way it was needed to make available for the Mooring System a connection Device and remote disconnection for permanent use in production and drilling units. This device, already approved for the classifying society, it is the hook KS32/40/50, one of the first open device used in permanent mooring systems in the world. This device presents as fundamental characteristic, the easy installation for at adverse environmental condition in Campos’ Basin, where the sea is Bimodal and Bi-directional (sea in development).
A Review of In-Place Design Approaches for Spar Hulls
Authors: Chen Cheng-Yo , Mills Trevor
Published: November 2008

This paper reviews the current practice for the in-place design of Spar hulls. Both the commonly-used approach and the state-of-the-art procedure for the maximum strength and fatigue conditions will be presented. Key assumptions for various design approaches will be discussed along with advantages and disadvantages of each approach. The review will focus on how each approach generates hydrodynamic loadings, performs global motions analysis, and maps design loads from motion analyses to structural finite-element model. Important aspects relating to Spar design will be addressed. In particular, effect of vortex induced hull motions (VIM) will be discussed, and an approach for including the VIM effect in the design of moorings and risers will also be described. Impact on the maximum strength and fatigue capacity of critical structural components due to the assumptions employed in the commonly-used design approach will be evaluated and quantified as compared to the results from the more rigorous state-of-the-art approach.
On the Reliability and Risk Analysis of Subsea Blowouts Preventers With Focused Attention on DP Rigs
Authors: de Moura Jorge Nilo
Published: November 2008

This paper provides a selection of findings on the reliability and risk analysis of submarine blowout preventers (BOPs) achieved in recent studies, which the author has participated among technicians in Petrobras and Rio de Janeiro Federal University - UFRJ. Petrobras is a deepwater E&P leading company and special attention has been given on the deepwater and ultra deepwater scenarios. Particular factors on the BOP for dynamic positioning (DP) rigs need to be accounted as far as risks on safety and downtime are concerned. The analyses have considered a comprehensive BOP reliability database that covers more than 12 years of experience, as well as, a collection of DP experience has been accessed during work. The riser safety margin tends to be unavailable as the water depth becomes deeper, and, so, in an emergency disconnection, the safety isolation of the well tends to be relied on the BOP mechanical barriers only. In this context, risks on different configurations of the BOP are compared and their results discussed with focused attention on main factors of risk. Finally, there has been visible progress on BOP reliability within recent years and a number of good operational practices in place are also mentioned in the paper.
Seismic and Structural Behaviour of Oil Storage Tank of Large Capacity
Authors: Salas Carlos Corte´s , Sa´nchez Sa´nchez He´ctor A.
Published: November 2008

This research has focused on the behavior, under seismic conditions, of already existing steel storage tanks of large capacity, located in high risk zones. From the revision of analysis and design criteria concerned with thin walls structures, it has been prepared a procedure based on a numeric modeling where the mechanic characteristics of the materials and the real geometrical measures have been considered. Numeric analysis by FEM have been used in different conditions: empty tanks vibration, full tanks where fluid-structure interaction is considered to the case of flexible walls, in order to take into account the pressure distribution of the liquid. To estimate the response, real seismic records originated in the Mexican Region, have been used. Finally the numerical results obtained of the empty tanks with those calculated analytically are compared and it is observed that a good correlation between both approaches. For the results obtained of the fluid-structure interaction models with the selected seismic registry is observed that given its great dimensions and the rigidity that provides the ring to them in the top part of the tanks, the effect of the surge is not very significant due to the fluid system — structure is excited in the first seconds, reason why the action of the hydrostatic pressure on the walls of these is sample to be dominant.
Assessment of the Operations of Floaters in Close Proximity
Authors: Ji Chunqun , Halkyard John
Published: November 2008

Field development in deep water often require floaters to be moored in close proximity, e.g. tender or offset drilling from spars, Dry Tree Units operating in conjunction with FPSOs. Mooring line interference is a key issue which needs to be considered in the design of the systems. This paper provides a study of this for a cell spar and semi-submersible operating in close proximity. Several nominal separation distances between the vessels were considered in the study. This paper presents an example for an initial separation distance of 530 ft (10% of the water depth). A time domain analysis of multi-vessel coupled responses and mooring line motion was performed to determine the potential of mooring line interference for a 100 year Hurricane and Loop Current condition. Results show that the 100 year Hurricane case would dominate for the mooring line interference for this case, and the interference for very close coupling might be avoided by pre-planning. In the worst case buoyancy might be added to the semi-submersible mooring to eliminate interference.
Database of Wave Energy Potential in Portugal
Authors: Pontes M. Teresa , Rebeˆlo Lui´s , Silva Pedro , Pata Ce´lia
Published: November 2008

Site selection for wave energy power plants is a complex procedure. In addition to enjoy good resource, the site should obey to certain geomorphologic and environmental conditions, comply with a number of restrictions to avoid conflicts of use, and enjoy close availability of specific infrastructures. Information on those topics is usually spread out through a number of institutions making their collection a time consuming task. In this paper a preliminary version of PEMAP, a database containing required information for this purpose for mainland Portugal, is presented. This database is implemented in a Geographical Information System. It contains information on wave energy resource, bathymetry, slope and seabed coverage of the mainland continental shelf and electrical grid among others. Near future development concerning engineering conditions such as information on harbors and shipyards, and marine biodiversity and fisheries is planned.
Spar Technology for Arctic Region Challenges
Authors: Murray John , Ji Chunqun
Published: November 2008

Arctic deepwater regions present special criteria for platform designs. These criteria include the ability to resist local and global loads from ice in addition to the loads conveyed by waves, wind and current. In some cases, a platform has to be moved to avoid contact with ice. This paper addresses the technical feasibility of a Spar design that can be disconnected from its mooring and riser system and towed out of the path of an encroaching iceberg. The paper also examines motions of the hull and load in the mooring lines in extreme loading conditions. The hull and mooring are sized for 100-year hurricane conditions in the North Atlantic region. Estimates of pack ice loading are compared to the responses and results show that the maximum mooring loads are governed by 100-year hurricane conditions and not the ice conditions. The paper presents conceptual design for quick release mooring and riser systems and preliminary dimension analyses of various components are provided.
A Benchmark Problem for Three-Dimensional Linear Hydroelasticity
Authors: Riggs H. R. , Huang L. L.
Published: November 2008

There has been substantial development in codes for three-dimensional linear hydroelasticity, but to the authors’ knowledge there does not seem to be any problems put forth in the open literature to serve as an appropriate benchmark problem for a floating structure. We present in this paper a detailed description of such a problem for three-dimensional hydroelastic computer codes. The structure is a rectangular, box-shaped ‘barge’ with dimensions 100 m × 10 m × 2 m. Its deformational response primarily involves vertical and horizontal bending. Detailed descriptions of the structure, the finite element structural shell model, and the hydrodynamic fluid model, based on the constant panel Green function method, are provided. Fine meshes are used to minimize discretization errors. Detailed results, including dry natural periods and modes, wet natural periods, and wave-induced displacements and stresses are presented. The detail is sufficient for others to use the problem as a benchmark for other codes.
Modeling Salt and Heat Dispersion From a Large Power and Desalination Plant in Abu Dhabi Emirate
Authors: Odeh M. , Mohamed Khaled A. , Areiqat Ahmed
Published: November 2008

Taweelah Power and Desalination Plant was built in Abu Dhabi Emirate, United Arab Emirates in 1995. The capacity of the plant was increased in 1998. At present, it was decided to carry out the second phase of the capacity extension to satisfy the rapid urban and industrial developments in the emirate. A comprehensive study was carried out to investigate the increased recirculation of salinity and temperature from the plant outfall to the intake due to the proposed extension. The study was carried out using a 3-dimensional numerical flow model simulates the tidal flows and heat transport in the vicinity of the plant. Recirculation of temperature at the plant intake was also obtained from the available long-term seawater temperature measurements at the intake and in the ambient seawater. The resulting recirculation of seawater temperature from the measurements was compared with the model results.
The Flow Around FPSO’s in Steep Regular Beam Waves: Results of PIV Experiments and RANS Computations
Authors: Huijsmans Rene´ H. M. , Graham Mike , Kendon Tim
Published: November 2008

This paper investigates the hydrodynamical aspects of a fixed FPSO in regular waves. The emphasis is geared to the validation of state of the art CFD techniques, using particle image velocimetry measurements on the water velocities around a captive model of an FPSO in regular waves. The main focus is on the following issues: Determination of the water velocities around the vessel using PIV techniques and pressures on a girth below and just above the mean waterline of the vessel using pressure gauges. Comparison of the detailed RANS simulations of the flow around the bilges of the FPSO. The resulting pressure profiles along the girth, especially near the waterline, showed a significant non-linear effect in steep beam wave conditions. The velocities as measured near the bilges of the vessel indicated a strong separation at the bilges of the vessel. This leads to an overestimation of the water velocities near the bilges of the vessel as calculated using a linear diffraction programme. The resulting pressure profiles along the girth, especially near the waterline, showed a significant non-linear effect in steep beam wave conditions. The velocities as measured near the bilges of the vessel indicated a strong separation at the bilges of the vessel. This leads to an overestimation of the water velocities near the bilges of the vessel as calculated using a linear diffraction programme. RANS simulations will give a more realistic flow profile around the bilges.
Time Variant Reliability of Mooring System Considering Corrosion Deterioration
Authors: Gao Zhen , Moan Torgeir , Heggelund Svein E.
Published: November 2008

This paper deals with time variant overload reliability analysis of a mooring system due to corrosion deterioration. A probabilistic model for uniform corrosion is adopted to predict the strength degradation. A simplified method and nonlinear finite element analysis are used to calculate the breaking strength of the chain link and comparison is made. The strength of one mooring line is modeled by a weakest link system. The effect of correlation in corrosion models for different chain links in one mooring line and the effect of higher corrosion rate in the splash zone are discussed. The annual failure probability of the most loaded mooring line of a semi-submersible is calculated. The first and second order motions of the semi-submersible and the corresponding line tensions are found by a simplified analysis. The time variant reliability analysis is performed by approximating the degraded strength by a piece-wise constant model. The annual failure probability is obtained for different years. It is found that the annual failure probability increases significantly as the chain is corroded.
Numerical Simulation of Accelerating and Decelerating Motion of a Submerged Body
Authors: Tzabiras George , Papadopoulou Vlasia
Published: November 2008

The present work deals with the numerical simulation of accelerating and decelerating motions of a submerged body of revolution, in order to investigate the influence of the thrust variation on the maneuvering characteristics. A finite volume method is adopted to solve the essentially 2D RANS, time-dependent equations in a body-fitted co-ordinate system. Two problems have been examined for a 50m body of revolution: (a) the stopping maneuver, i.e. crash stop from steady forward speed and then full astern and (b) full ahead at steady speed from rest and then full astern.
Time Domain Simulations on a Single Point Moored Submerged Sphere of Variable Radius
Authors: Cruz Joa˜o M. B. P. , Sarmento Anto´nio J. N. A.
Published: November 2008

This paper presents a different approach to the work developed by Cruz and Sarmento (2005), where the same problem was studied in the frequency domain. It concerns the same sphere, connected to the seabed by a tension line (single point moored), that oscillates with respect to the vertical direction in the plane of wave propagation. The pulsating nature of the sphere is the basic physical phenomenon that allows the use of this model as a simulation of a floating wave energy converter. The hydrodynamic coefficients and diffraction forces presented in Linton (1991) and Lopes and Sarmento (2002) for a submerged sphere are used. The equation of motion in the angular direction is solved in the time domain without any assumption about its output, allowing comparisons with the previously obtained results.
Validation of an Analytical Method to Calculate Wave Setdown on Current
Authors: Voogt Arjan , Bunnik Tim , Huijsmans Rene´
Published: November 2008

This paper describes an analytical model to calculate the setdown in waves with and without current. This model is based on a second order quadratic transfer function and a Lagrangian transformation for the effect of current. The method is validated against basin experiments with a large number of wave probes through the basin. The wave signals are separated in incoming and reflected bound and free waves based on the phase differences between the wave probes. The optimum probe spacing and transient phenomena in the restricted sized basin are discussed. The resulting separated bound wave shows good comparison to the setdown calculated with the analytical model.
Analysis of Wave Run-Up Measurements on a Mini-TLP
Authors: Sibetheros I. A. , Niedzwecki J. M. , Teigen P.
Published: November 2008

Wave run-up on deepwater offshore structures may contribute to wave overtopping of the platform deck. It may also cause undesirable loads including impact loads on the underside of the deck when combined with other hydrodynamic phenomena beneath the platform deck. In this study a 1:40 scale model of an unmanned mini-TLP design was subjected to a series of design sea environments for the Gulf of Mexico. Complimentary testing of compliant and fixed hull configurations was performed and the wave run-up was measured at several locations around the hull in both head and quartering sea orientations of the platform. The wave elevation data reported here was obtained at three critical points on the hull and a reference wave gage well upstream of the model. Analysis of the data was performed using an orthogonal third order Volterra series system analysis technique. The wave run-up measurements were compared and correlated to the incident wave elevation measurements. The results indicate that the run-up is more pronounced in the rigid hull model configuration than for the compliant model configuration and this was the case for both headings. Further, the analysis revealed a strong linear relationship between wave run-up and the incident wave field over the high wave energy frequency band. This result adds credence to the previously proposed simplified computational procedures for estimating the second order wave run-up on large cylinders in random waves.
Full Scale Data Comparison for the Horn Mountain Spar Mooring Line Tensions During Hurricane Isidore
Authors: Tahar Arcandra , Finn Lyle , Liagre Pierre , Halkyard John
Published: November 2008

The Horn Mountain Production Spar was installed in 5,400 feet of water in June 2002. This was the deepest floating production unit at that time. A comprehensive instrumentation program was initiated to measure spar and riser responses (Edwards et al, DOT 2003), while motion comparisons were presented on previous publication (Halkyard et al, OMAE 2004). The present paper discusses the results of these measurements and compares with analytical predictions of spar mooring tension during hurricane Isidore in September 2002. Particular attention has been placed on the importance of Coulomb friction between wire chain and the fairlead bearing to the dynamic tension of mooring lines. Mooring tensions were measured at chain jack location (inboard tension), while analytical models computed those tensions at the fairlead location (outboard tension). Our conclusion is that there is excellent agreement between field measurements and computed tensions at the chain jacks when fairlead friction is included, and when the vessel motions are accurately predicted. Ignoring fairlead friction results in a slightly conservative estimate for the tension at the chain jack. This has been the standard practice in all spar designs to date.
High Lateral- and Temporal-Resolution Current Sampling: Measurement Set-Up and Some Findings
Authors: Kleiven Gudmund , Eide Lars Ingolf
Published: November 2008

This paper presents two high temporal resolution current measurement campaigns where the current is sampled and stored at a frequency of 1Hz. One of the campaigns also included high lateral resolution measurements. The measurements were part of the current measurement program conducted by the Ormen Lange project. The measurements are rather unique and the first successful campaigns of its kind on the Norwegian Continental Shelf. The main objective of these measurements was to measure the turbulence characteristics of the current flow. This was regarded as important input to the design of the numerous free pipeline spans in the Ormen Lange development resulting from the very uneven seabed in the area. The frequencies of particular importance were the frequencies of the first eigenmodes of the free pipeline spans being in the range 0.1–1 Hz. The measurements confirm the shape of the turbulence following the Kolmogorov –5/3 decay law in this frequency range. Measurements along the pipeline route did not reveal any significant differences in the near seabed turbulence intensity along the route. Extrapolating the measurements into a near seabed record mean current speed of 0.5m/s gives a turbulence intensity of approximately 0.1. The high lateral resolution measurements demonstrate local topographic influence on record mean current. This concerns topographic steering, damping and amplification of current speed.
Microstructural Design for High Strength Steel Welds: The Concept of Duplex Microstructure
Authors: Liu Stephen
Published: November 2008

In the past three decades, Colorado School of Mines researchers have investigated flux-related welding processes for pipeline applications and systematically characterized the fundamental behavior of welding fluxes. They also established the relationships between flux ingredients, weld metal microstructure, and weld joint mechanical properties. These studies clarified for high strength steel welds the importance of the bimodal nature of weld metal inclusions, related to weld metal transformations. As strength and toughness levels of the steels continue to increase, new generations of consumables must be developed. Two novel consumables design concepts are being investigated at the CSM. The first one is based on a duplex microstructure consisted of lath martensite and ferrite, and the second is based on low carbon, high alloy martensite.
The Numerical Simulation of Green Water Loading Including Vessel Motions and the Incoming Wave Field
Authors: Kleefsman K. M. Theresa , Loots G. Erwin , Veldman Arthur E. P. , Buchner Bas , Bunnik Tim , Falkenberg Erik
Published: November 2008

This paper presents results from simulation of green water loading including vessel motions. The simulation is performed through a domain decomposition: the far field and ship motions are calculated by potential theory and are used to simulate the local flow around the deck of an offshore floater using a Navier-Stokes solver. In the solver the free surface is displaced using a Volume of Fluid based method, improved by introducing a local height function. First, simulations of an irregular wave, where the velocities at the boundaries of the domain are prescribed using results of a linear diffraction code are performed in order to check wave propagation properties. Then, the same code is used to initiate the simulation of an FPSO in high waves, resulting in green water on the deck.
Wet Ageing of Syntactic Foams Under High Pressure/High Temperature in Deionized Water
Authors: Gimenez Nelly , Sauvant-Moynot Vale´rie , Sautereau Henry
Published: November 2008

Syntactic foams (hollow glass microspheres embedded in an organic matrix) were traditionally dedicated to buoyancy applications and are now used for thermal insulation purpose. The paper focuses on the hygrothermal ageing of such materials with model diepoxy/diamine thermoset matrix having high Tg and controlled architecture revealed by the mechanical and thermal properties and by gravimetric measurements. The ageing of syntactic foams of different volume fractions is studied under the combination of both high pressure / high temperature conditions (up to 300 bar / 100°C) to discuss the factors governing the long-term performance of these materials. Attention is paid to the degradation phenomenon observed on the foam after matrix has reached saturation and associated with markedly increase of mass gain. This study points out how the hydrolytic ageing of glass microspheres may reduce the durability of syntactic foams used in hot wet conditions.
Enhancement of Design Criteria for Fish Farm Facilities Including Operations
Authors: Berstad Are Johan , Tronstad Harald , Sivertsen Stein-Arne , Leite Endre
Published: November 2008

A Norwegian Standard NS 9415 (NAS, 2003) has been introduced to the offshore fish farming industry in Norway. This is the first standard dealing with offshore fish farm facilities. The main objective of the standard is to reduce environmental pollution by fish escape. The work process leading to NS 9415 revealed the need for research work in several areas to enhance design criteria with the objective of having a consistent safety level through out the life cycle of a fish farm facility. This paper presents results from a government supported research project with the objective of enhancing criteria for design and operation of fish farm facilities. A case study of a fish farm facility representative for the majority of polyethylene based fish farms in Norway is presented and the sensitivity of such fish farms to variation in the mooring system is shown and discussed for design relevance. The sensitivity of net cage volume to current and weights is presented and discussed. Possible hazards from operational conditions are listed.
Experiences Using DNV-RP-F105 in Assessment of Free Spanning Pipelines
Authors: Fyrileiv Olav , Mo̸rk Kim , Chezhian Muthu
Published: November 2008

Free spans often become a challenge in pipeline design and operation due to pipeline installation on uneven seabed or seabed scouring effects. The costs related to seabed correction and span intervention are in many projects considerable. Therefore it is relevant to investigate whether such intervention work is necessary or not. Despite the complexity inherent in free span response, the spans are often designed applying presumably conservative concepts and very simple analytical tools. The DNV guideline no 14 (GL14) for free spanning pipelines was issued in 1998 and has later been updated and issued as an Recommended Practice (DNV-RP-F105) to account for recent technical research and development and accumulated experience applying GL14 in pipeline projects. This code allows vortex induced vibrations (VIV) as long as the pipeline integrity is ensured, by for example checking that the fatigue life is sufficient. By giving design methodology and acceptance criteria for fatigue, the DNV-RP-F105 approaches the real physics of free spans in a better way than older codes and makes it possible to select cost-effective methods both in the design phase and later when re-assessing spans in the operational phase. This paper will briefly discuss some experiences obtained by using the DNV-RP-F105 in free span design/re-assessment. Some examples of pipeline failures due to free span and vortex induced vibrations will also be presented.
Control of Large-Scale Impacts by Designed Structural Damping
Authors: Wigaard Jan , Hoen Christopher , Haver Sverre
Published: November 2008

Modification of deep-water floaters often involves module installation using a floating crane vessel. The impact forces caused by relative motions between the floating vessels represent a major challenge during set down on the floater deck due to the large inherent variability of these forces. Traditionally the difficulties in predicting impact forces during module installation have been overcome by the use of experienced based rules of thumb rather than accurate simulations and calculations. One has to some degree relied on the indeed present but un-quantifiable effect of human intelligence of the operation supervisor. Traditionally the impact forces are taken either by elastic deformation of the module itself and/or the installation guides or by permanent deformation of intermediate structural elements through e.g. plastic yielding of ductile metal members or crushing of wood members. Designing the module and the guides to be able to take the entire probable range of impact forces is difficult due to the inherent contradiction between wanted flexibility and required strength. The large uncertainties of the impact energy imply that it is difficult to design these intermediate elements to cover all possible impact energy levels. Furthermore, these elements cannot be applied in cases where repeated impacts may occur. An attractive alternative to the traditional solutions is application of industrial shock absorbers. The performance of these is predictable and they can be designed to cover the estimated range of impact energy. This paper will present a more precise and consistent design and analyses methodology that gives a more accurate measure on the reliability of the operation in accordance with code requirements. The paper will show application of industrial shock absorbers as an alternative to traditional solutions for impact handling during offshore module installation to floating vessels, illustrated with experience gained by the installation of two modules on the Visund Semi. Results from multi-body simulations and model tests comparing traditional methods with the proposed solution will be given. The significant benefits obtained with respect to increased operational performance, reduced acceleration loads on the installed equipment, the increased predictability of the operation, and the consistent safety level in accordance with code requirements, will be highlighted. The possibility to apply designed damping for other offshore applications like dropped object protection etc, is also discussed.
Designing Structural Damping to Avoid Resonance Problems in Structures, Piping and Subsea Equipment: Risk Reduction and Fatigue Life Improvement
Authors: Wigaard Jan , Hoen Christopher , Fredo¨ Claes R.
Published: November 2008

For weight optimised deep-water structures as well as subsea equipment and piping, designing for dynamic loading from e.g. ocean waves, rotating and pulsating equipment is a challenge. A special case is the acoustic vibrations experienced in the steel piping in either end of flexible risers. Excessive vibrations have been experienced both on topside and on subsea equipment. To the authors knowledge, fatigue failure in gas containing pipes has been the result in at least two known cases, one due to acoustic vibrations, and another caused by a traditional piston compressor. During the design process it is generally a problem to predict the inherent level of damping in the structures or the equipment in order to estimate the response as accurately as possible. Much effort has been spent trying to predict the inherent damping. However, little has been done to deliberately increase structural damping in order to reduce the dynamic response significantly. Controlled application of structural damping is an alternative to changing stiffness or inertia characteristics of the structure to avoid resonance, and is often the only solution for broadband loading where resonance cannot be avoided. This paper describes solutions for two types of frequently occurring resonance problems on offshore installations and discusses general possibilities for the use of designed damping. One solution, applicable for high frequency acoustically induced vibrations in piping, is successfully applied on a full-scale mock-up of a pipe segment with a blind flange and a flange with valve, representing two real world problem details. The applied damping solution is a tailored design. Another example shows use of standard industrial dampers for vibration control of a piston compressor skid. The latter is implemented offshore and by visual control vibrations were significantly reduced. On site measurements will be conducted later. The paper will cover design and construction of the actual vibration dampers including selection of damping material. Selection of damping material depends on the occurring frequency and temperature range. The dampers should be designed to obtain maximum damping effect given the stiffness, inertia, excitation and response amplitudes of the structure. Avoiding resonance by designing natural frequencies away from excitation frequencies is sometimes close to impossible. Therefore, the deliberate addition of damping to substructures at which high stress is expected at high frequency and localized vibration is probable, can be a fatigue and risk reducing design measure that by far exceeds anything that can be achieved through other means.
Model Experiments of Hydrodynamic Forces on Heave Plates
Authors: Chua Kie Hian , Clelland David , Huang Shan , Sworn Andy
Published: November 2008

For truss SPAR platforms, damping plates are employed to increase the added mass and viscous drag in the heave direction. The paper aims to investigate experimentally the hydrodynamic forces on heave plates with different opening sizes. Model scale experiments were carried out on three 40 by 40cm flat plates to investigate the effects of oscillation amplitude and opening size on the hydrodynamic forces acting on the plates whilst undergoing forced heave motion. Three different methods of data processing were investigated, namely, directly processing unfiltered data to obtain the hydrodynamic coefficients, filtering the data before evaluating the coefficients and fitting the filtered data to a sine curve before evaluating the coefficients. The most accurate method was then selected and used to evaluate the experiment results. The coefficient values obtained were compared with the published data available. The effects of various variables such as opening size, KC number, frequency of oscillation on the hydrodynamic coefficients were also studied. Relative magnitudes of the drag and inertia components of the overall hydrodynamic load are compared.