bluuebunny/crossref_metadata_2025 huggingface dataset:
Time and Frequency Domain Analysis of Catenary Risers Subjected to Vortex Induced Vibrations
Authors: Larsen Carl M. , Passano Elizabeth
Published: October 2008

Catenary risers in deep waters will experience conditions with insignificant wave forces in combination with strong current. The response will in such cases be dominated by vortex induced vibrations (VIV). Dynamic bending stresses will vary along the riser, but a large peak will almost always be seen near the touch down point. This peak is caused by the restrictions on riser displacements from the presence of the seafloor, and the local bending stresses will be influenced by stiffness and damping propertoes of the bottom. Analysis models based on finite elements will represent the interaction between riser and seafloor by discrete springs, which for the linear case will remain constant independent of the displacements. This type of model may give a significant over-prediction of bending stresses at the touch down point since a linear spring will give tensile forces instead of being released and allowing the pipe to lift off from the bottom. A non-linear time domain model will, however, account for changes by releasing springs if tension occurs and adding in new springs if free nodes obtain temporary contact with the bottom. The results will hence become far more realistic. Traditional empirical models for VIV prediction are based on a frequency domain dynamic analysis with constant stiffness. There is hence an obvious need for improvements when dealing with catenary risers. This paper will describe a new approach that is based on combined use of an empirical linear frequency domain model for VIV, and a non-linear model for time domain analysis. The first step is to carry out the VIV analysis according to linear response theory, and next introduce the calculated hydrodynamic forces to the non-linear structural model. The benefit from using the non-linear model is that stresses in the touch down area are described more accurately. A case study is also reported. Bottom stiffness and friction are varied, and results are compared to a simple model with a hinge at the touch down point. The conclusion is that the interaction between riser and seafloor is crucial for accurate stress prediction, and that a non-linear time domain model will give the most accurate result.
Implicit and Explicit Implementation of the Dynamic Relaxation Method for the Definition of Initial Equilibrium Configurations of Flexible Lines
Authors: da Silva Danilo Machado Lawinscky , Jacob Breno Pinheiro , Rodrigues Marcos Vini´cius
Published: October 2008

Recent activities in the offshore oil exploitation industry require new structural concepts employing flexible lines (both mooring lines and risers). Such systems present increasingly complex configurations, with dynamic nonlinear behaviour; therefore, the use of efficient numerical solution procedures, based on the Finite Element Method, becomes mandatory for their analysis. The usual analysis procedure for flexible lines by the FEM is based in the calculation of an initial, stable static equilibrium configuration in order to define the finite element mesh. Usually this configuration is obtained by the classic catenary equations. However, in more complex problems these equations cannot be applied. Therefore, the objective of this work is to present the use of a more general finite element approximation, associated to dynamic relaxation algorithms. Such algorithms can be started from arbitrary configurations, not necessarily in equilibrium. The resulting procedure is accurate, robust, and avoids numerical problems such as the ill-conditioning of the tangent stiffness matrix, allowing the static equilibrium configuration to be obtained in an efficient way.
A Generalized Contact Model for Nonlinear Dynamic Analysis of Floating Offshore Systems
Authors: da Silva Danilo Machado Lawinscky , Correˆa Fabri´cio Nogueira , Jacob Breno Pinheiro
Published: October 2008

The objective of this work is to present the implementation of a contact model that represents, during a nonlinear dynamic analysis of floating offshore systems, the contact of lines with the platform, as well as the contact involving different lines and, eventually, involving two different platforms in the same model. Traditional contact models consider for instance a generalized scalar element, consisting of two nodes linked by a non-linear gap spring. In this work, the contact model is geometrically defined by volumes that cannot interpenetrate. A penetration stiffness can be defined for each volume; lateral friction can also be considered by this model. An appropriate data structure is used to define the volumes and guarantee the efficiency of the algorithm by an optimized search. The application of the presented contact model is demonstrated by case studies of actual applications for offshore systems: pipelines in S-Lay installation operations, where the contact is complex, specified only in some points of the ramp and stinger; offloading floating hoses that may collide with the hull of the ship, and catlines in lift operations.
Numerical Simulations of Large Deep Water Waves: The Application of a Boundary Element Method
Authors: Hague Caroline H. , Swan Chris
Published: October 2008

This paper concerns the description of extreme surface water waves in deep water. A fully nonlinear numerical wave model in three dimensions is presented, based on the Boundary Element Method (BEM), and is applied to nonlinear focusing of wave components with varying frequency and direction of propagation to form highly nonlinear groups. By using multiple fluxes at corners and edges of the numerical domain the “corner problem” associated with BEM-based models in physical space is overcome. A two-dimensional version of the method is also employed to model unidirectional cases, and examples presented include the focusing of Top Hat spectra in deep water to form highly nonlinear wave groups at or close to their breaking limit. The ability of the model to accurately simulate these sea states is highlighted by comparison to the fully nonlinear model of Bateman, Swan and Taylor (2001, 2003).
Experimental and Numerical Evaluations of Aluminum Drill Pipes Under Cyclic Loads
Authors: Lourenc¸o Marcelo Igor , Netto Theodoro A. , Silva Neilon S. , de Miranda Paulo Emi´lio Valada˜o , Pla´cido Joa˜o Carloes Ribeiro
Published: October 2008

Experimental program and numerical analyses were carried out to investigate the fatigue mechanisms of aluminum drill pipes designed and manufactured in compliance with ISO 15546. Material mechanical properties, including S-N curve, were determined through small-scale tests on specimens cut from actual drill pipes. Full-scale experiments were also performed in laboratory. Initially, the tool-joint assembly procedure was actually performed to monitor the resulting strain/stress level in selected points of the aluminum pipe. Three full-scale aluminum drill pipe specimens were then fatigue tested under combined cyclic bending and constant axial tension. In parallel, a finite element model of the tool-joint region, where two drill pipe specimens failed in the fatigue tests, was developed. The model was first used to reproduce the tool-joint assembly. Then, the physical experiments were simulated numerically in order to obtain the actual stress distribution in this region. Good correlation between full-scale and small-scale fatigue tests was obtained by adjusting the strain/stress levels monitored in the full-scale tests in light of the numerical simulations.
A Coupled-Mode Technique for the Run-Up of Non-Breaking Dispersive Waves on Plane Beaches
Authors: Belibassakis K. A. , Athanassoulis G. A.
Published: October 2008

A coupled-mode model is developed and applied to the transformation and run-up of dispersive water waves on plane beaches. The present work is based on the consistent coupled-mode theory for the propagation of water waves in variable bathymetry regions, developed by Athanassoulis & Belibassakis (1999) and extended to 3D by Belibassakis et al (2001), which is suitably modified to apply to a uniform plane beach. The key feature of the coupled-mode theory is a complete modal-type expansion of the wave potential, containing both propagating and evanescent modes, being able to consistently satisfy the Neumann boundary condition on the sloping bottom. Thus, the present approach extends previous works based on the modified mild-slope equation in conjunction with analytical solution of the linearised shallow water equations, see, e.g., Massel & Pelinovsky (2001). Numerical results concerning non-breaking waves on plane beaches are presented and compared with exact analytical solutions; see, e.g., Wehausen & Laitone (1960, Sec. 18). Also, numerical results are presented concerning the run-up of non-breaking solitary waves on plane beaches and compared with the ones obtained by the solution of the shallow-water wave equations, Synolakis (1987), Li & Raichlen (2002), and experimental data, Synolakis (1987).
Vortex-Induced Motion: Model Testing of a Monocolumn Floater
Authors: Cueva Marcos , Fujarra Andre´ L. C. , Nishimoto Kazuo , Quadrante Lui´s , Costa Ana Paula
Published: October 2008

The vortex-induced vibrations - VIV have been studied for several fields of engineering due to its occurrence in different structures, such as electrical cables, industries chimneys and offshore risers. Although available an extensive literature describing its fundamental issues, these vortex-induced phenomena still deserve investigation, particularly in the offshore platforms installed in regions with high current speed. Recently, the Vortex-Induced Motions - VIM, a particular case of vortex-induced vibration with high magnitude of response amplitude, have been observed in SPAR platforms installed in Gulf of Mexico - GoM, opening a new investigation field. For those motions, aspects such as asymmetric mooring restoring stiffness and the probable three-dimensionality of the flow turn the problem even more complex. Since 2003, in partnership with University of Sao Paulo and consultant companies, PETROBRAS has been studying the use of monocolumn floaters for oil production in Campos Basin and GoM. Considering the environmental conditions in these areas and assuming that monocolumn floaters can exhibit similar VIM behavior of SPAR platforms, it was started an experimental investigation focusing on VIM responses of small-scale monocolumn floaters in towing tank. Although based on the state of art procedures used for SPAR platforms, the monocolumn experiments considered the different geometry of this concept and the larger susceptibility to the three-dimensional effects, due to the smaller relation draft/beam. Special attention was given to the ratio roughness/beam in order to guarantee similarity between the experiments and its respective real cases. Additionally, different heading conditions were also tested. Thus, the present work presents a set of preliminary results and discussions concerning VIM of monocolumn floaters and its impact on the mooring line design and riser specification.
Innovative Ice Protection for Shallow Water Drilling: Part I — Presentation of the Concept
Authors: Gu¨rtner Arne , Gudmestad Ove Tobias , To̸rum Alf , Lo̸set Sveinung
Published: October 2008

Recent discoveries of hydrocarbons in the shallow waters of the Northern Caspian Sea arise the need for intensive drilling activities to be carried out in the near future in order to explore the potentials. Experience with mobile drilling units in the seasonally ice infested waters solely originates from the current drilling campaign of the Sunkar drilling barge at Kashagan and Kalamkas. However, with increased drilling activities upcoming, innovative drilling concepts are desirable due to the objective of maintaining drilling operations during the ice period with conventional non-ice-resistant drilling platforms. Hence, this paper suggests the employment of external Shoulder Ice Barriers (SIBs) to protect a conventional jack-up drilling rig from the hazards of drifting ice in shallow water. The SIB’s design is suggested to increase the ice rubble generation at the ice facing slope and thereby provide sufficient protection from drifting ice impacts. The modular concept of the SIB makes it possible to deploy each module in a floating mode to site, whereupon they are ballasted and connected to each other, forming a sheltered position for the jack-up. Subsequent to the termination of the drilling campaign the SIB modules may be retrieved by de-ballasting and tow out, without having significant impact on the environment. This paper presents, on a technical feasible level, the concept of ice protection in shallow water by means of SIBs.
Development of Floating System for Recovery of Lithium From Seawater
Authors: Zhou Guoqiang , Yao Xiongliang , Sun Liping
Published: October 2008

In the study, a floating system for recovery of lithium from seawater was presented. The floating system consists of adsorbent tanks with double hull and double bottom structures. Several key technologies are developed for the system, such as non-return valve, adsorbent tank, swash bulkheads in adsorbent tanks, double hull structures with inlet holes on inner bottom and ballast tanks in side hulls. Seawater flows into double bottom structures from suction holes on the bilge, then flows into the adsorbent tanks through the non-return valves on inner bottom, and passes through the piled adsorbent. Finally seawater is discharged out of the adsorbent tanks from drain holes on the sheer strake by drain pumps. A floating tank integrated with the key technologies was modeled and the model test was carried out at sea. In addition, an economic assessment on the system has been made. The study results demonstrate that the proposed floating system is promising and the system technologies are reliable.
Effects of CO2 Ocean Sequestration on Marine Fish
Authors: Ishimatsu Atsushi , Hayashi Masahiro , Kikkawa Takashi , Kita Jun
Published: October 2008

Ocean sequestration of CO2 has been proposed as a possible measure to retard the increasing rate of the atmospheric CO2 concentration. Since some negative impacts on marine animals and ecosystems are likely to ensue, we must carefully investigate biological effects of ocean CO2 sequestration before embarking on this mitigation practice. Considering the expected depths for CO2 ocean sequestration (> 1,000 m), it is desirable to use deep-sea animals for the experimental assessment of CO2 ocean sequestration. In addition, experimental protocols preferably mimic environmental conditions at the releasing site: CO2 concentrations vary due to mixing with surrounding seawater at low temperatures (0–2 °C) and under high pressures. This paper describes our recent experiments to elucidate the effects of high CO2 on marine fishes. A deep-sea fish Careproctus trachysoma (habitat depth 400–800 m) can be captured alive and be used for in vivo CO2 exposure experiments. 100% mortality occurred when the fish was exposed to seawater equilibrated with a gas mixture containing 3% CO2 conditions at 2 °C within 48 h, whereas mortality was never observed when shallow-water fishes (Mustelus manazo, Paralichthys olivaceus and Seriola quinqueradiata) were tested under the same CO2 conditions but at higher temperatures (17–20 °C). It is currently not clear whether this difference in mortality is due to often presumed high susceptibility of deep-sea organisms to environmental perturbations. Subsequent experiments demonstrated that low water temperature accelerates mortality by CO2 exposure. Thus, half lethal time decreased from 105h to only 5 h when water temperature was decreased from 26 °C to 20 °C (CO2 8.5%, Sillago parvisquamis). Therefore, the high CO2 susceptibility of C. trachysoma could be solely due to low water temperature. Temporally varying CO2 conditions resulted in markedly different mortality patterns when compare with mortality recorded under constant CO2 conditions. Step-wise increases in ambient CO2 resulted in much lower mortalities than under one-step increases to the same CO2 levels. Further, a sudden drop of CO2 from 9–10% CO2 to air level (0.038%) killed all the surviving fish within a few minutes.
The Required Collaboration Between Universities and Government Administration in Plans for the Regeneration of Ports and Harbors That Utilize the Appeal of Marine Space
Authors: Hirao Naoyuki , Kondo Takeo , Yamamoto Kazukiyo , Koishikawa Masao , Watanabe Kiyoaki
Published: October 2008

Marine space has a variety of appealing elements such as in use as resorts, for leisure, marine sports, physical distribution and the function involving the flow of people. However, ports and harbors that have lost their physical distribution functions and are steadily declining are on the increase. The Ministry of Land, Infrastructure and Transport is attempting to undertake regeneration of such ports and harbors that have lost their vitality from the middle of the 20th century. To date, regeneration plans for ports and harbors have been under the initiative of government administration but today, plans for the regeneration of ports and harbors and measures for revitalizing port towns are being reviewed in various ways including the creative development of communities through participation of the local citizenry and the convening of workshops by NPOs. As a part of this, the Chiba Port and Harbor Office in which the national government invests has begun a trial attempt to launch new projects for the invigoration of port towns through the formation of a program under which plans for the regeneration of ports and harbors and the invigoration of port towns will be undertaken through the collaboration of universities and local administrative governments. As a forerunner to such a model project, a program to form a regeneration plan for Kisarazu Port through the collaboration of Kisarazu and the Department of Oceanic Architecture & Engineering of Nihon University for senior 4th year students with the national government’s Chiba Port and Harbor Office as the moderator has been undertaken. At Nihon University, in the curriculum of Oceanic Architecture, A Planning Studio, 7 teachers and 58 students participated and 14 classes with three hours each week were conducted. This paper introduces the background to this and reports on the status of local contribution by the university.
Research on the Recommended Lighting Environment for the Safe Utilization of Marine Space
Authors: Koizumi Yusuke , Kondo Takeo , Yamamoto Kazukiyo , Arai Masato
Published: October 2008

The Inland Sea (Seto Nai Kai) is a sea area with many cross-sea bridges and a very high level of sea traffic. There is concern regarding the adverse impacts of such illumination sources as road lighting, up-lighting and cable illumination for a number of cross-sea bridges on the operation of fishing boats and large liners. The possible effects of bridge illumination on the safety of sea traffic have been discussed by the Honshu-Shikoku Bridge Authority since the planning stage for bridges linking Honshu Island and Shikoku Island over the Inland Sea and detailed investigations and experiments have been repeatedly conducted. This study was initiated based on the belief that it is of crucial importance to verify the propriety of the standards for bridge illumination set by the Authority for fishermen and ship operators navigating around and under these bridges as some 10 years have now passed since the completion of all of the planned bridges. A questionnaire survey with fishermen and ship operators was conducted under the study to evaluate the effects of bridge illumination. As a result, it was found that bridge illumination poses no problems for the safe navigation of ships, proving the propriety of the road lighting standards set by the Authority.
Computational Fluid Dynamics for the Simulation of Oil Recovery Systems at High Seas
Authors: Clauss Gu¨nther F. , Kosleck Sascha , Abu-Amro Mazen
Published: October 2008

The paper presents multi-phase CFD-Calculations for simulating oil skimming processes in heavy seas. During the last years tanker catastrophes showed the shortcomings of existing oil recovery systems, especially while operating in heavy seas. For developing new and more efficient devices complex and expensive model tests must be conducted under special conditions to prevent environmental pollution. To minimize these costs CFD-tools for multi-phase flow simulations have been developed, and are applied to analyse and optimize oil recovery devices. The analysis of local flow phenomena dependent on the motion of an oil recovery system in a given sea state are the basis for the development of an optimized oil recovery device. For this purpose, existing nonlinear numerical methods used for stationary and unsteady viscous computation (based on Volume of Fluid (VOF) methods and Reynolds Averaged Navier Stokes Equations (RANSE)) are enhanced and combined to simulate two-phase (air, water) and three-phase-flow (air, water, oil). New methods for simulating motions in three (2D) and six degrees (3D) of freedom as well as for the generation of waves — regular and irregular sea states — are developed. To increase the speed of calculation the RANSE/VOF-method is coupled with a Potential theory method using Finite Element discretization (Pot/FE). Combining the advantage of the Pot/FE-solver, i.e. calculation speed, with the possibilities of the RANSE/VOF-solver to simulate multi-phase flow and free body motion offers the opportunity to simulate a complete test in reasonable time. To validate the procedure, the numerical simulations are compared to WAMIT-calculations and model tests carried out in a physical wave tank.
The Use of Computer Simulation in Developing Procedures for Marine Hazard Countermeasures
Authors: Artana Ketut Buda , Ishida Kenji , Baliwangi Lahar
Published: October 2008

IMO (International Maritime Organization) has so far been producing several conventions with objective to ensure safety of ship operation and pollution prevention. In practice, however, implementations are rather exigent since some countries that ratified the conventions face so many difficulties due to mainly lack of fund and human resources. To solve this problem, efforts in educating people for marine hazard prevention and countermeasure must be supported by giving chances to people to get experiences directly in marine hazard prevention and countermeasure through performing simulation using computer. This can be made possible by setting marine accident or incident scenarios and participants involve in the simulation process will represent all parties related to marine Hazard countermeasures. This research is mainly aimed to develop and evaluate essential technological and engineering hardware and software for encountering marine hazard as well as essential risk management system, covered organizers and human resources, which have proper judgment ability and leadership. This research is also directed to seek optimum alternative method to train and educate people to get knowledge and experience on hazard prevention. The simulation is provided with a database system which eases the participant in performing their tasks. Responses to each scenario will be optimized by comparing three (3) indicators, namely: cost, resources and time for task completion. At the end of the simulation, a formal procedure for the countermeasure can be designed which guarantee those three indicators are minimum. A data mining system is also attached to the simulation to enable the database system automatically classifies the data according to the responses of the participants.
Statistics of Extreme and Freak Waves
Authors: Lopatoukhin Leonid J. , Boukhanovsky Alexander V.
Published: October 2008

Wind waves are of the main hazards, affecting the human activity and needed for shipbuilding design, near shore facilities, planning and management of coastal and port operation, etc. Wave climate investigations, based on continuous 30-year hindcasting are performed. One of the main results of hindcasting is a set of two-dimensional spectra S(ω,θ) on selected grids and synoptic terms t, in particularly. For statistical generalization as the tools, multivariate statistical analysis is used. Special attention is drawn to point and field extremes. Specific and difference between these two statistics is crucial for solution of some applied problems. Adjusted approaches do not allow investigating phenomena known as freak (or rogue) waves. The main difference between extreme and freak waves is in their unusual form. Probability of freak wave depends from a lot of internal and external reasons. Some approaches are proposed and described in this paper.
Effect of Structural Member Uncertainties in the Jacket Type Offshore Platform Assessments
Authors: Asgarian B. , Amiri M. M.
Published: October 2008

In the assessment of an old jacket type offshore platform, the Reserve Strength Ratio (RSR) should be computed and it is used for accepting or rejecting the platform for the future. There are many parameters affecting the Reserve Strength Ratio of such a structure. One of the important parameter is the bias factor (Br) of the structural element ultimate capacity. The bias factor is defined as the ratio of best estimate or true values to the nominal or predicted values. This parameter must be obtained for all structural elements including bracing members (in buckling or tension), joint strength, and piles lateral capacity by considering actual behavior of element material. Most of the recommended bias factors for the structural elements are evaluated from experimental results. In this paper, a review on the parameters affecting Reserve Strength Ratio of the Jacket Type Offshore Platforms subjected to Metocean loading is performed and a method is presented for the obtaining of bias factor related to structural element capacity. The method is applied to evaluate assessment of three sample platforms in the Persian Gulf. The results in terms of RSR are compared with the analysis results using previous recommended bias factors.
Hydrodynamic Wave Loading on Offshore Structures Simulated by a Two-Phase Flow Model
Authors: Wemmenhove Rik , Loots Erwin , Veldman Arthur E. P.
Published: October 2008

The numerical simulation of hydrodynamic wave loading on different types of offshore structures is important to predict forces on and water motion around these structures. This paper presents a numerical study of two-phase flow over a sloping bottom with the presence of breaking waves. The details of the numerical model, an improved Volume Of Fluid (iVOF) method, are presented in the paper. The program has been developed initially to study the sloshing of liquid fuel in satellites. This micro-gravity environment requires a very accurate and robust description of the free surface. Later, the numerical model has been used for calculations of green water loading and the analysis of anti-roll and sloshing tanks, including the coupling with ship motions. The model has been extended recently to take two-phase flow effects into account. Two-phase flow effects are particularly important near the free surface, where loads on offshore structures strongly depend on the interaction between different phases like air and water. Entrapment of air pockets and entrainment of bubble clouds have a cushioning effect on breaking wave impacts. The velocity field around the interface of air and water, being continuous across the free surface, requires special attention. By using a newly-developed gravity-consistent discretisation, spurious velocities at the free surface are prevented. Thus far, the second air phase has been treated as incompressible. Taking compressibility effects into account requires a pressure-density relation for grid cells containing air. The expansion and compression of air pockets is considered as an adiabatic process. The numerical model is validated on several test cases. In this paper special attention will be paid to the impact of a breaking wave over a sloping bottom.
A Lattice Boltzmann Bluff Body Model for VIV Suppression
Authors: Frandsen Jannette B.
Published: October 2008

In this paper, the suitability of a mesoscopic approach involving a single phase Lattice Boltzmann (LB) model is examined. In contrast, to continuum based numerical models, where only space and time are discrete, the discrete variables of the LB model are space, time and particle velocity. With reference to the Boltzmann equation of classical kinetic theory, the distribution of fluid molecules is represented by particle distribution functions. The LB method simulates fluid flow by tracking particle distributions. It is notable that the formulation avoids the need to include the Poisson equation. An elastic-collision scheme with no-slip walls is prescribed. The central idea behind proposing the present formulation is many fold. One goal is to capture smaller scales naturally, postponing the need of applying empirical turbulence models. Another goal is to get further insight into nonlinearities in steep and breaking free surfaces to improve current continuum mechanics solutions. Although the long term goal is to predict bluff-body high Reynolds number flows and breaking water waves, the present study is limited to laminar flow simulations and continuous free surfaces. The case studies presented include bluff bodies embedded in Reynolds number flows in the order of 100–200. The free surface test cases represent bore propagation past a single and multiple structures. The 2-D uniform grid solutions are compared with findings reported in the literature. Vortex patterns are studied when single or several objects are located in the bluff-body wakes. From a mitigation point of view, the model presents an easy means of re-arranging bluff bodies to study optimum solutions for VIV suppression with/without a free surface.
Influence of the Ballast Tanks Loading on the Allowable VCG in Damage Case
Authors: Rueda Guilherme , Madella Bruno , Nishimoto Kazuo , Matsumoto Fabio
Published: October 2008

The aim of this paper is the study of the Allowable VCG in monocolumn offshore platforms. As study case the MonoBR — an innovative conceptual unit developed by a partnership of PETROBRAS/CENPES and University of Sa˜o Paulo — was analyzed. The studies were carried out during the design of MonoBR for the Walker Ridge area, Gulf of Mexico. The effect on the stability of the unit caused by a damaged tank depends on its loading condition, since there is lost of both, buoyancy and mass, modifying unit’s displacement and center of gravity. In other words, depending of the tank loading, the amount of water that enters or leaves the unit in a damage case may vary widely. In this paper is presented the methodology adopted in the study of influence of the ballast tanks loading in the Allowable VCG curve in MonoBR, introducing this other variable beyond the draft, the usual single variable in AVCG curves. At the end are presented the main results for the study case, whose AVCG can vary by 50% for the same draft depending of the tank loading.
Stability Analysis of a MPSO (Mono-Column Floater, Production, Storage and Offloading Unit): MonoBR
Authors: dos Santos Bruno Madella R. , Rueda Guilherme E. , Matsumoto Fabio Tadao , Campos Felipe C. R. , Dos Santos Costa Ana Paula , Nishimoto Kazuo
Published: October 2008

The MonoBR is a MPSO — mono-column floater, production, storage and offloading unit — a unique platform designed to handle steel catenary risers (SCR) in a depth of 1800 m in Gulf of Mexico oil fields whose target scenario is the ultra-deep water of the Walker Ridge. In this project, special concern was given to sea keeping behavior, constructability and security. Stability Analyses were carried out to ensure the system security and reliability. This paper describes the development carried out by The University of Sa˜o Paulo and PETROBRAS team, in order to analyze the main stability parameters of this new conceptual design for oil production and storage, the MonoBR. The main topics referred on the text are the damaged and intact stability analyses, the tank arrangement, wind influence, rules discussions, the AVCG (Allowable Vertical Center of Gravity) and damage compensation through ballast rearrangement.
Measurements of Wave Induced Hull Girder Vibrations of an Ore Carrier in Different Trades
Authors: Storhaug Gaute , Moe Erlend , Holtsmark Gabriel
Published: October 2008

Currently, the conventional wave loading is the only effect considered in fatigue assessment of ships. DNV has recently confirmed that fatigue damage from wave induced vibrations may be of similar magnitude as from the conventional wave loading (Moe et al. 2005). A 40% contribution to the total fatigue damage in deck amidships is documented through extensive measurements onboard an ore carrier (the reference ship) trading in the North Atlantic. The effect of strengthening the vessel, increasing the natural frequency by 10%, is ineffective to reduce the relative magnitude of the vibration damage. The wave induced vibration, often referred to as whipping and/or springing, does contribute to fatigue damage also for other ship types and trades (Moe et al. 2005). This paper considers the effect of trade. It indicates when the wave induced vibrations should be accounted for in the design phase with respect to fatigue damage. A second ore carrier (the target ship) is monitored with respect to the wave induced hull vibrations and their fatigue effect. Stress records from strain sensors located in the midship deck region are supplemented by wave radar and wind records. Based on the measurements, the vibration stress response and associated vibration induced fatigue damage are determined for varying wind- and wave forces and relative headings. While the reference ship operates in the Canada to Europe ore trade, the target ship trades between Canada and Europe, Brazil and Europe, and South Africa and Europe. A procedure is suggested by Moe et al. (2005) to estimate the long term fatigue damage for different trades by utilizing the measured data from the reference ship. The vibration and wave damage are considered separately. By comparing the measured wave environment and the DNV North Atlantic scatter diagram, the effect of routing indicated a reduction of the fatigue damage by one third. A slightly revised procedure is applied to estimate the effect of trade for the second ore carrier, comparing the long term predicted fatigue damage with the measured fatigue damage. The importance of trade is confirmed. However, the relative contribution of the vibration damage is shown to increase in less harsh environments. The target ship vibrates more than the reference ship for the same trade and Beaufort strength. The vibration damage of the target ship constitutes 56% of the total measured damage, and the high natural frequency is observed to have no significant effect.
Integrated Dynamic Analysis of Floating Offshore Wind Turbines
Authors: Nielsen Finn Gunnar , Hanson Tor David , Skaare Bjo̸rn
Published: October 2008

Two different simulation models for integrated dynamic analysis of floating offshore wind turbines are described and compared with model scale experiments for the Hywind concept for floating offshore wind turbines. A variety of both environmental conditions and wind turbine control schemes are tested. A maximum power control strategy is applied for wind velocities below the rated wind speed for the wind turbine, while a constant power control strategy is achieved by controlling the rotor blade pitch for wind velocities above rated wind speed. Conventional rotor blade pitch control for wind velocities above rated wind speed introduces negative damping of the tower motion. This results in excitation of the natural frequency in pitch for the tower and may lead to unacceptable tower motions. Active damping of the undesirable tower motions is obtained by an additional pitch control algorithm based on measurement of the tower velocity.
Status Review on Fatigue Performance of Fillet Welds
Authors: Maddox Stephen J.
Published: October 2008

This paper presents a critical review of current design methods, including their background and relevant experimental data, for assessing the fatigue performance of steel fillet welds with respect to failure in the weld throat. The main focus is on fillet or partial penetration welds in cruciform, T or lap joints under transverse loading failing by fatigue crack growth across the weld throat under normal stresses. The review covers the influence of residual stress, applied mean stress, joint fit-up and alignment, weld quality, the use of coated steel, the need for a plate thickness correction and calculation of the optimum weld size. Also considered are cases of fillet welds failing in shear or combined normal and shear stresses.
The Motions of a Ship on a Sloped Seabed
Authors: Buchner Bas
Published: October 2008

In standard diffraction theory it is assumed that the water depth is constant and that the seabed is infinitely large. To account for a local varying bathymetry in shallow water (as it can occur for offshore LNG terminals) it is sometimes considered to introduce a second fixed body on the seabed representing this bathymetry in diffraction theory. Based on the results presented in this paper it can be concluded that this is (without special measures) not possible. The refraction and interference effects are too strong and affect the wave exciting forces on the LNG carrier in an incorrect way. A large size of the second body and smoother edges of this body do not improve the situation. However, a second body in diffraction theory, when chosen properly with respect to size and shape, can contribute to the correct calculation of the added mass and damping of vessels on sloped seabeds as this varies with the local water depth over the length of the vessel. This will clearly affect the motion response of the vessel. This can be seen for instance in the pitch-heave coupling. This will influence the motions of the ship in waves, as well as the resulting drift forces and related mooring loads.
Mooring System and Motion Response Analysis of a Gas Import Floating Terminal in Operating and Survival Conditions
Authors: Chatjigeorgiou Ioannis K. , Thanos Ioannis , Bourma Paraskevi , Mazarakos Thomas , Mavrakos Spyros A.
Published: October 2008

The present work is dealing with the quasi-static motion response analysis of a Gas Import Floating Terminal that is moored through a turret mooring system. The results of the analysis presented here is part of the work undertaken by the Division of Marine Structures, School of Naval Architecture and Marine Engineering, National Technical University of Athens (NTUA-MS), within the GIFT project that is supported by the EU (GIFT, 2005). The results concern the response of the mooring system and the associated behavior of the floating terminal under specific operating and survival conditions. In addition to the quasi-static responses, the slowly varying motions of the vessel are calculated by applying appropriate frequency domain solution techniques. Finally, some first comparisons between the numerical predictions and pertinent experimental data of physical model tests are given and discussed.
A Study of LES Models for the Simulation of a Turbulent Flow Around a Truss Spar Geometry
Authors: Sirnivas Senu , Allain O. , Wornom S. , Dervieux A. , Koobus B.
Published: October 2008

A new generation of LES type model is used to simulate the flow around a Spar geometry. This new method involves a Variational Multiscale formulation, allowing better capture of the back scatter. This approach is well suited for flows where small scales transmit a notable amount of energy to larger ones. The flow simulation is compared with experimental data from a model test.
Wave Spectral Bandwidth as a Measure of Available Wave Power
Authors: Smith George H. , Venugopal Vengatesan , Fasham Jack
Published: October 2008

A key requirement in the description of the performance of a wave energy converter is how the efficiency of power capture changes with the properties of the sea. This paper examines the effect of two generic power transfer functions (PTF) on power production from six simulated wave spectra. These were chosen to represent a series of wind, wind-swell mixed and swell dominated seas. The spread in energy within the sea state as defined by a variety of bandwidth parameters was examined to determine if there was a correlation between the width of the transfer function and the sea bandwidth. It was found that, for the ‘constant’ height PTF, the bandwidth parameter Bb (calculated using zeroth, minus-one and minus-two spectral moments) provided the best correlation. Customary bandwidths ε and ν performed poorly. When the PTF was allowed to vary in height as well as width there was little improvement in correlation from the un-scaled results.
Time Scale of Scouring Around Submarine Pipelines Induced by Wave and Current
Authors: Bakhtiary Abbas Yeganeh , Mousavi Mir Emad , Vahdat Amin Tohidi
Published: October 2008

Physical experiments have been conducted to explore the time scale of the wave- and current- induced local scouring around submarine pipelines as well as the development of the scour profile versus the elapsing time. The experimental results have been used to examine the recommended equations of Fredsoe et al. (1992) and/or to derive new equations for prediction of scour depth/width during the process with respect to the equilibrium scour properties. In addition, the total duration (time scale) of scouring is studied and a new equation is proposed for the case of current motion. The results of this equation are then simplified in the form of diagrams for estimation of the scouring duration in practice.
Ultimate Limit State Assessment of the M.V. Derbyshire Hull Structure
Authors: Paik Jeom Kee , Seo Jung Kwan , Lee Jae Myung , Park Jae Hyung
Published: October 2008

The Capesize bulk carrier, M.V. Derbyshire, sank in the North West Pacific during typhoon Orchid in September 1980 when she was on a voyage from Canada to Japan carrying fine iron ore concentrates. Since then, extensive investigations of the vessel sinking have previously been made in the literature primarily by the formal safety assessment (FSA) technique to explore the loss causes, but serious speculation on the failure of hull structures has been lacking in such investigations. The present paper investigates the possibility of the vessel sinking initiated by the failure of hull structures rather than by other loss scenarios such as hatch cover failure subsequent to water ingress into the cargo holds. Ultimate limit state assessments of individual stiffened panels and hulls of the M.V. Derbyshire under extreme bending moments during the last voyage in storm are made using ALPS/ULSAP and ALPS/HULL computer programs. It is concluded that the M.V. Derbyshire could have sunk by hull girder collapse with or even without unintended water ingress into cargo holds. Important insights and findings developed from the present study are summarized.
Qualification of High Strength Carbon Steel Wires for Use in Specific Annulus Environment of Flexible Pipes Containing CO2 and H2S
Authors: Taravel-Condat Carol , Desamais Nicolas
Published: October 2008

Flexible pipes have been used for many years in offshore applications for the transportation of crude oil, gas and water. Such structures are subjected to mechanical loads due to tension, high internal pressure and dynamic motions which are sustained by the use of high strength carbon steel wires. The steel wires are located in the annular space that may contain water and acid gas (CO2, H2S) which can be detrimental for steels. For that reason, risks of Sulfide Stress Corrosion Cracking (SSCC) and Hydrogen Induced Cracking (HIC) shall be considered. Moreover, for dynamic conditions, presence of corrosive environment in the annulus could significantly reduce the fatigue performance of flexible pipe compared to air environment. The annulus composition is calculated using a permeability model that has been validated with medium scale tests, full scale tests and field cases [1]. In parallel, corrosion and corrosion fatigue studies have shown that the annulus of a flexible pipe is a very confined space with over-saturation in iron and no renewal of oxygen. This results in a higher pH, much lower corrosion rates and less HIC and SSCC than one would expect based on normal environments. This paper presents, in a first part, the different results obtained during small scale corrosion and corrosion fatigue tests demonstrating the beneficial specificity of the annular space. In a second part, the paper presents the results of pH measurements and corrosion rates obtained during a full scale dynamic corrosion fatigue test in CO2/H2S environment validating the previous results. This test was conducted on a 6” pipe between 1999 and 2003. In a third part, the paper describes how the annulus specificities should be used today to determine the suitability of carbon steel wires for use in flexible flowlines and risers considering SSCC, HIC, corrosion and corrosion fatigue.
Self Standing Hybrid Riser System in Waves and Current
Authors: Pereira Paulo Se´rgio D. , Morooka Celso K. , Shiguemoto Denis A. , Coelho Fabio M.
Published: October 2008

Nowadays, the hybrid riser system concept is considered an alternative system in ultra-deep water up to 3000 meters for offshore petroleum production. Compared with other systems, the Self Standing Hybrid Riser (SSHR) proves to be a good alternative. The system is composed by three main components: a vertical riser connected to the seabed, a subsurface buoy close to the sea surface, and a flexible riser connecting the buoy to a floating production facility. Despite desirable performance of the overall concept, many problems still remain in the design of this type of riser system dealing with oil and gas production or exporting petroleum production. In the present study, dynamic behavior of a vertical riser with a subsurface buoy near the sea surface is described. Hydrodynamic loads due to currents and waves in the direction of the loads and in the transverse direction due to vortex shedding are considered. Critical points are addressed throughout time domain calculations in terms of riser vortex induced vibration (VIV) and in-line motions due to current and waves. The influence of buoy oscillations on the riser behavior is observed. For a first attempt of a developed model, comparisons have been carried out with experimental results.
A Computational Investigation of the Effect of Geometric Parameters on the Discharge Rate of a Ship Opening
Authors: Nabavi Yasser , Calisal Sander M. , Akinturk Ayhan , Klaptocz Voytek
Published: October 2008

The purpose of the research was to find a relationship between the geometric characteristics of an opening on deck and the water discharge rate. This study is aimed at the stability of open deck ferries and fishing vessels. The effective parameters on the discharge rate are the beam, depth of the water collected on the deck, and the discharge gap height. In this study, CFD analyses for water discharge from a ship deck were conducted, and the commercial code FLUENT was used to conduct the simulations. A two dimensional unsteady 2nd order solver in time and space was used for the simulation. The two-phase free surface model was simulated by the Volume of Fluid (VOF) method. Using the water discharge, the instantaneous depth Froude number was calculated as a part of the non-dimensional simulation. The effect of geometric parameters on the water discharge rate was investigated by keeping two parameters fixed while changing the third parameter. For each parameter, three different values were evaluated and the comparisons of all the twenty seven possible combinations of the effective parameters were presented. Results were compared with the experimental results obtained earlier at UBC.