bluuebunny/crossref_metadata_2025 huggingface dataset:
Design Aspects of Green Water Loading on FPSOs
Authors: Buchner Bas , Lopez-Cortijo Garcia Joaqui´n
Published: January 2009

Green water is a significant problem for floating ship-type offshore structures, which needs to be assessed in the early design of the structure. First the present paper summarises a new semi-empirical design evaluation procedure that can assist in this design process. Then the practical design considerations related to the green water problem are discussed. There are different ways to solve the green water problem for a particular structure at a specific location: • Design the vessel and structures on the deck against the predicted green water impact load levels. • Optimise the bow shape (underwater shape and above water bow flare). • Increase the freeboard height such that green water is prevented completely. • Increase the freeboard height such that the green water loads are reduced to acceptable levels and design for these load levels. • Optimise the structures on the deck to minimise the green water impact loads. • Use protecting breakwaters in front of critical structures on the deck. All these options have their advantages and disadvantages. The semi-empirical design evaluation method and the different design options are discussed in a case study, focussing on a new DP FPSO concept.
Design of Self-Stabilizing Ice Barrier
Authors: Weihrauch Alexandra , Berger Joachim , Bartels Marc
Published: January 2009

Ice barriers installed in close vicinity to offshore platforms are designed to take the main loads resulting from floating ice by breaking the ice and piling-up the rubble ice. Platforms and equipment protected by ice barriers can be dimensioned considering only low ice loads and can thus be constructed more economically. Also, the safety of the platforms increases. One objective of the research project MATRA is to design suitable ice barriers for exploration and oil production in ice-covered, shallow-water areas. Several concepts were investigated, e.g. vertical and inclined piles as well as barges equipped with piles. Model tests were carried out under varying conditions in order to evaluate the design alternatives and to provide the design loads resulting from floating ice. The most suitable structure is a light-weight ice barrier with an inclined roof structure mounted on a barge which collects early, thin ice inside the structure, stabilizes itself by the piled-up rubble ice and by this later can withstand thicker ice. The measured loads were analysed and compared with loads theoretically derived from existing approaches. At the first stage, when the structure fills with ice, bending is the dominant failure mode. Once a rubble pile has built-up in front of the structure, other failure modes may become significant comprising buckling and crushing. The load-time curve shows a scattering behaviour and has very high load peaks of short duration, especially for thick ice. The analysis comprises a statistical evaluation of the loads, taking the site conditions in the Caspian Sea as reference. Design loads for different load-cases were derived, which are the basis for the stability analysis of the ice barrier. On the basis of the results of the stability analysis and considering the requirement that the structure shall be self-floating for transport, the structure was optimized and the detail design was carried out.
Dynamic Behaviour of Compliant Towers in Deep Sea
Authors: Clauss Gu¨nther F. , Lee June Young
Published: January 2009

For oil and gas production in deep water (> 500m) compliant structures are designed. By dedicated reduction of stiffness and optimization of mass (including added mass contributions) the fundamental period is tuned to about 30s, which is well above the period range of significant wave energy. This paper presents the results of a comprehensive numerical analysis of the hydroelastic behaviour of compliant towers in deep water, investigating the dynamic response of a flexible structure in a given sea state. The numerical program system is based on ADINA with an integrated hydrodynamic module for wave/structure interaction. Nonlinear effects of viscous forces are considered using Morison’s vector equation. In addition nonlinear characteristics of soil/structure interaction are also included according to API regulations. At first, for verification of the program system, the numerical results of a monotower are compared to analytical solutions obtained by modal analysis of the structure in regular and irregular seas. Based on the validated program a compliant tower installed in 503 m water in the Gulf of Mexico (Baldpate tower) is modeled in 3D, and the characteristic dynamic behavior is evaluated. Finally, the tower is exposed to a real “freak” wave (the 25.6m high New Year Wave which has been registered at the North Sea Draupner platform on January 1, 1995), and the associated loads and motions are evaluated.
Development of Safer Ships by Deterministic Analysis of Extreme Roll Motions in Harsh Seas
Authors: Clauss Gu¨nther F. , Hennig Janou , Cramer Heike , Kru¨ger Stefan
Published: January 2009

For modern ship design — as confirmed by many examples of ship design and operation — the current intact stability code (IMO (2002)) does not provide a reliable basis for the assessment of ship safety in rough seas. In ship design the application of the IS-Code is not supporting design decisions towards increased safety in rough seas (Cramer and Kru¨ger (2001)), and ship operators find their cargo and/or vessels endangered by large roll angles and accelerations (France et al. (2001)). Thus, there is a great need for procedures to analyze ship safety in rough seas. This paper presents innovative deterministic seakeeping test procedures which are used to identify the physical mechanism endangering intact ships by evaluating cause-reaction relations of wave/structure interaction. Rogue wave sequences are embedded in severe seas for computer controlled capsizing tests of different vessels at the Hamburg Ship Model Basin. The model test results are used as a basis for the development of non-linear numerical methods to simulate ship motions in extreme seas with the target to design safer ships with reduced capsizing risk. Polar plots following from the non-linear simulations allow the evaluation of ship safety in severe seas with reference to course, speed and trim.
Evaluation of the Dynamic Behavior of the P50 FPSO System Using Dynasim: Comparison With Experimental Results
Authors: Palazzo Fabio G. , Sparano Joa˜o V. , Simos Alexandre N. , Masetti Isaias Q. , Tannuri Eduardo A.
Published: January 2009

The P50 system is a Floating Production Storage and Offloading System under construction for future operation at Brazil’s Campos Basin, in a water depth of approximately 1200 m. The system is based on a VLCC vessel, moored in DICAS (Differential Compliance Anchoring) system and presents a reasonably large riser porch on the portside for 77 lines. In this paper the dynamic behavior of the offshore system is evaluated using Dynasim, a time-domain simulation code for moored offshore systems, developed by the University of Sa˜o Paulo and Petrobras. Simulations are compared with experimental results. Two kinds of tests were performed: “Calibration” tests were carried out in order to obtain static coefficients of the hull under isolated current and wind loads. “Validation” tests were conducted to evaluate the dynamic behavior under extreme environmental conditions combining current and wave excitation. First and second-order motions were measured as well as mooring line tensions for three different drafts of the ship. A generally good agreement was observed between numerical simulations and experimental results, reassuring the reliability of the numerical code.
Sway Platforms: Influence of Configuration, Topside Weight and Design Philosophy on Structural Reliability
Authors: Ronalds B. F. , Pinna R. , Trench D. J. , Cosson D. G. , Cole G. K.
Published: January 2009

Moment magnification in platforms such as monopods and jack-ups may be addressed in a variety of ways in the design process. This paper investigates how differing treatments influence the reserve strength ratio (RSR) and hence structural reliability of sway platforms. Both WSD and LRFD versions of API RP2A are considered, together with several methods of estimating the moment magnification factor. The effect of varying topside weight is also incorporated — increasing topside load increases the second order moments but also increases the amount of steel provided by the Code to resist the loadings. It is found that the RSR varies widely for different structural configurations and may either increase or decrease with increasing topside weight. The RSR is also sensitive to the design approach adopted. As a result, a single set of partial load factors will not succeed in narrowing the spread of reliabilities across different configurations and design philosophies. Indeed, the use of a WSD format may result in more uniform reliability levels than API RP2A-LRFD for certain sway platforms.
Response of Topside Structures to Fires and Explosions: Recent Findings
Authors: Burgan Bassam A. , Hamdan Fadi H. , Barker Darrell D. , Puskar Frank J.
Published: January 2009

The design of topside structures to resist hydrocarbon fires and explosions necessitates consideration of a range of issues not normally addressed by the designer. This paper gives an overview of the key issues that have been studied in several sponsored R&D projects and by the Fire and Blast Information Group (FABIG). The results are presented in a form that is usable by designers. The main areas covered are: • Elevated temperature material property design data for use in fire engineering. • High strain rate material property design data for use in explosion resistant design. • Analysis techniques for fire and explosion design. • Design methods based on codified rules (i.e. covered by design standards) and advanced techniques.
Effect of the Yield to Tensile Ratio, Y/T, on Structural Reliability of Linepipes
Authors: Ernst Hugo A. , Villasante Jose´ A. , Izquierdo Alfonso
Published: January 2009

The effect of the Yield (Y) to Tensile (T) ratio, Y/T, on the structural reliability of linepipes with longitudinal defects was studied in this work. A model based on elastic-plastic fracture mechanics (EPFM) and plasticity theory, was developed for that purpose. The analysis allows for load or deformation control situations. The results are shown in terms of curves of critical defect size vs. the controlling variable, i.e. load or deformation. For each one of the several materials studied, different cases with different Y/T values were considered. Even for the lower limits of experimental data, i.e. larger Y/T, the materials have adequate defect tolerance.
Deployment of Subsea Equipment in Ultradeep Water
Authors: Morrison Denby , Cermelli Christian
Published: January 2009

This paper describes various options to deploy subsea equipment in ultra-deepwater. The methodology used to study the feasibility and cost of the various options is presented. The focus of this paper is the performance of the numerical tools compared with offshore observations. Both offshore measurements and wave tank data are emphasized in this paper in order to validate the numerical model. Two possible contributors to more benign offshore response compared with calculations are: (1) complex subsea package hydrodynamics, and (2) wire rope damping effects. Indications are that internal damping in the very long, and relatively complex, wire ropes used offshore, is a source of significant damping. This damping is helpful in mitigating resonance effects.
An Experimental Investigation on the Bending Behaviour of Flexible Pipes
Authors: Troina Le´a M. B. , Rosa Lui´z F. L. , Viero Paula F. , Magluta Carlos , Roitman Ney
Published: January 2009

A flexible pipe is a composite structure, built up of several steel and plastic layers, which has been increasingly used in floating offshore petroleum production systems. It is characterized by presenting low bending stiffness and high capacity with regard to internal and external pressure and tension. In order to determine some physical properties of a flexible pipe specimen, which is useful for a global analysis, and to better understand the behaviour of its tensile armour layers, when the pipe is submitted to low tension loads, a series of experimental tests were performed by COPPE/UFRJ and CENPES/PETROBRAS. In this context, bending tests, with internal pressure variation, were carried out on a 4” internal diameter flexible pipe. In some specific cross sections, the outer plastic sheath of the specimen was removed to enable the installation of electrical extensometers in the tensile armour layer. Some experimental results were compared to those obtained through analytical models, and the discrepancies are discussed.
Dynamic Compression of Rigid and Flexible Risers: Part II — Comparison of Theoretical and Experimental Results
Authors: Simos Alexandre N. , Fujarra Andre´ L. C. , Alves Karime H.
Published: January 2009

In a previous paper, experimental results on the dynamic compression of rigid (steel catenary) and flexible risers were presented. Tests considered different combinations of amplitude and frequencies of top motion and distinct current velocities. In this paper, dynamic tension estimations obtained through finite element analysis and analytical formulation are compared to the experimental results. Tension amplitude and critical compression load values are evaluated and compared both for the steel catenary (SCR) and flexible models. Comparisons have shown, in general, a fair agreement between theory and experiments, reassuring the reliability of numerical models. The results also demonstrate that the analytical formulation applied provides reasonable predictions of maximum tension loads and is able to cope well with the variation of critical load with the frequency of motion.
Analysis of the Influence of Mechanical Properties on the Residual Stress in Offshore Chain Links Using the Finite Element Method
Authors: Pacheco Pedro M. Calas Lopes , Kenedi Paulo Pedro , Jorge Jorge Carlos Ferreira , de Paiva Augusto M. Coelho
Published: January 2009

Production offshore units have a relative long operational life (about 20 years), during which are submitted to the ocean adverse environment loading produced by the combination of wind, waves and currents. This complex loading history can promote the nucleation and propagation of cracks in mooring line components. The presence of defects establishes a critical situation that can lead to catastrophic failures. In spite of residual stress plays a preponderant part in the structural integrity of a mechanical component, the presence of residual stress is not considered in traditional design of these mechanical components. Therefore, is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. The present contribution regards on modeling and simulation of the residual stress distributions in studless chain links using a tri-dimensional elastoplastic finite element model with large displacements. In the analysis three material conditions, associated with different mechanical properties, were considered. The results indicate that the presence of residual stresses modify significantly the stress distribution in the component. Also, residual stress distribution depends on the mechanical properties of the chain link material. The structural integrity of the mechanical component was studied using the concept of critical volume associated to the material volume susceptible to a certain critical crack size. This methodology permits the evaluation of the critical crack length distribution related to brittle fracture of the component.
Flow Characteristics of Artificial Steel Reefs
Authors: Shin Hyunkyoung
Published: January 2009

In order to develop novel types of artificial steel reefs suitable for marine environments near the Korean Peninsula, it is very important to carry out model tests in the initial design stage. In the Ocean Engineering Wide Tank (L×B×Dw = 30×20×2.5m) and the Circulating Water Channel, both of the University of Ulsan, Korea, fluid drag forces acting on models of artificial steel reefs with three different sizes were measured in waves and currents and flow characteristics were observed. The comparison between test results and numerical predictions based on the Navier-Stokes equation showed a good agreement and the verification enabled to predict numerically characteristic of flow past the reefs in the designed sea conditions.
Fatigue From Vortex-Induced Vibrations of Free Span Pipelines Using Statistics of Current Speed and Direction
Authors: Yttervik Rune , Larsen Carl M. , Furnes Gunnar K.
Published: January 2009

A section of a sub sea pipeline that is suspended between two points on an uneven seafloor is often referred to as ‘a free span pipeline’. Pipelines, installed on a seabed with a highly irregular topography, may have to be designed with several free spans. If a free span is exposed to a current flow, vortex-induced vibrations (VIV) of the suspended part of the pipeline may occur. These vibrations may cause unacceptable fatigue damage in the structure. Statistical distributions of current speed and direction close to a small mountain on the seabed (approximately 20 m high and 40 m wide) are established based on full-scale measurements of the current velocity in the area. Some results from recent model tests of VIV in free span pipelines, including some tests in which the flow direction was not perpendicular to the longitudinal axis of the pipe, are shown. These results indicate that it is sufficient to use the component of the current velocity vector that is normal to the pipe when using empirical models for estimating the response due to vortex shedding. An existing empirical model for analysis of VIV [1] is extended such as to include oscillations in the same plane as the current flow (in-line VIV). The effect of including the directional variability of the current when estimating the VIV fatigue damage, using the extended VIV model on a typical free span pipeline, is demonstrated, and found to be of great importance. A parameter study, in which the length of the free span is varied, is also carried out. The conclusion from this study is that a reduction of free span length affects the parameters that govern the accumulation of fatigue damage differently. Stresses are increased, but the number of current conditions capable of inducing VIV is reduced when the length of the span is reduced. It is therefore difficult to predict whether the accumulated damage will increase or decrease when the span length is reduced, and detailed analyses are required for each particular free span and current distribution. The damage from in-line VIV is generally lower than the damage from the cross flow VIV for all but the shortest span lengths.
Flexible Riser Fatigue Evaluation for FPSO’s in Bi-Directional Sea Spectra
Authors: Duarte de Lemos Carlos Alberto , Vaz Murilo Augusto , de Siqueira Marcos Queija
Published: January 2009

The fatigue calculation methodology applied to flexible risers connected to FPSOs, offshore Brazil, is based on a simplified procedure considering a deterministic regular wave approach and a wave heading distribution supported by past operational experience with semi-submersible platforms. However the utilization of deterministic waves approach does not necessarites guarantee the consideration of the worst sea conditions, and the weathervaning capability of those systems are usually not accounted for when non-collinear wave, wind and current are present. A new procedure is being evaluated considering an integrated model for ship, mooring lines and risers to define the distribution of ship headings for fatigue analysis using an irregular bi-directional sea approach. The impact on a flexible riser’s fatigue life will be evaluated when a new ship heading distribution with irregular bi-directional spectrum is presented for the case of a FPSO with bow turret in operation at the Marlin Field offshore Campos Basin.
Generation of Wave-Field Time Histories by the Modulated Discrete Fourier Transformation
Authors: Li Yousun
Published: January 2009

In the time domain simulation of the response of an offshore structure under random waves, the time histories of the wave field should be generated as the input to the dynamic equations. Herein the wave field is the wave surface elevation, the water particle velocities and accelerations at structural members. The generated time histories should be able to match the given wave-field spectral descriptions, to trace the structural member motions if it is a compliant offshore structure, and be numerically efficient. Most frequently used generation methods are the direct summation of a limited number of cosine functions, the Fast Fourier Transformation, and the digital filtering model. However, none of them can really satisfy all the above requirements. A novel technique, called the Modulated Discrete Fourier Transformation, has been developed. Under this method, the wave time histories at each time instant is a summation of a few time-varying complex functions. The simulated time histories have continuous spectral density functions, and the motions of the structural members are well included. This method seems to be superior to all the conventional methods in terms of the above mentioned three requirements.
Local Energy Spectra in the Vicinity of an Extreme Wave Event
Authors: Gibson Richard , Swan Chris
Published: January 2009

Previous work by Baldock, Swan and Taylor [1], Johannessen and Swan [2,3], and Bateman, Swan and Taylor [4,5] has demonstrated that in the vicinity of an extreme wave event there are significant and rapid changes in the local wave spectrum. The present paper combines two recent advances. The first is a new fully nonlinear directional wave model, the application of which is particularly suited to the description of extreme waves arising in realistic sea states. The second involves recent advances in time-frequency analysis techniques. Unlike traditional spectral analysis, based upon the Fourier transform, these allow local and rapid changes in a wave spectrum to be clearly identified. By combining these methods the proposed paper will first highlight the occurrence of these changes in realistic seas and will subsequently demonstrate their significance both in terms of estimating crest height elevations and in predicting the associated water particle kinematics.
Up-to-Date of Seismic Design Spectrum for Offshore Platforms at the Bay of Campeche
Authors: Garci´a Vargas Joel A. , Pe´rez Marti´nez Roberto
Published: January 2009

This paper presents the procedure proposed by the ISO code adapted to the local conditions in the Bay of Campeche, Mexico in order to obtain design spectrum for different seismic reserve capacity factors. A probabilistic seismic hazard analyses is used in order to determine the uniform hazard spectrum where the seismic environment, according to previous researches, is influenced by three primary types of earthquake sources: the subduction zone on the western pacific coast of Mexico, the lithospheric slab within the central portion of Mexico and the trans-mexican volcanic belt. This earthquake spatial distribution can be shown trough the historic catalog of earthquake occurrences during the period 1900–2001 used. On the one hand, in the evaluation of the characteristics and the uncertainties associated with the earthquake sources and their effects on the interest sites, are taken into account the characterization of the earthquake sources, the effect of the seismic wave propagation, the local conditions and the soil-structure interaction developed during earthquake ground motions. On the other hand, the uncertainties on the seismic hazard curve and those associated with the platform behavior (mass, stiffness, damping) in which their values are assigned to be consistent with the ISO 19901-2 and ISO 19902 seismic code suggestions. The final result consists in a seismic design spectrum for offshore platforms at the Bay of Campeche, which are consistent with the recommended ISO 19902 seismic reserve capacity factors, modified for local soil conditions, following a detailed seismic-action procedure.
Quantitative Determination of Safety Integrity Level on Offshore Metering and Custody Transfer Facility
Authors: Di´az-Herna´ndez Alejandro , Pe´rez Medina Mari´a Eloisa , Gonza´lez Rafael Melo
Published: January 2009

A quantitative way for determining the Safety Integrity Level of Safety Instrumented System (SIS) on Offshore Metering and Custody Transfer Facility in Campeche Bay Mexico is presented in this work. The methodology that was employed in order to assess and determine the Reliability parameters of SIS; which was carried out in three steps: 1. Identify undesirable events that can damage to personnel using the API-14C and to, the facility and the environment (by oil spill in hoses when the oil tanker is filled), 2. Estimate the severity and consequences of risk, using safety layer matrix of ISA S84.01 and, 3. Quantify the severity of each risk identified with the fault tree analysis. This last step uses the minimal cut sets, an innovative concept in petroleum industry, this provides valuable information about possible combinations of fault events, that can result in a critical failure of the system. The period of maintenance of the main SIS components (sensors, logic solver and final element), was reduced applying redundancy in the primary element. Furthermore, the results obtained of this analysis can be used by insurance companies or institutions that certify under standards of process quality and safety.
Ultra-Deepwater Floating Platforms Simulation on SPAR Realistic Marine Virtual Environment System
Authors: Cunha Gerson Gomes , Petrus Levy Luis Augusto , Santos Lopes Maria Ce´lia , Landau Luiz
Published: January 2009

This paper presents a new system for offshore floating petroleum platforms design and simulation using virtual reality technology. Environmental conditions and visual effects were introduced together the analysis results to build a realistic experience. The system integrates the capabilities of a large scale design system PROSIM, for design and evaluation of floating structures, mooring lines and rigid or flexible risers under wave, wind and current effect; and SPAR system, for realistic visual effects and environmental conditions representation to enhance the visual perception and phenomenon understanding. It will be presented a real case usage of the system in the project of new floating platform with wave, wind and terrain data of the Campos Basin (Brazilian biggest reservoir). The real-time simulation of floating systems is not new, but until today only scientific aspects were considered besides visual appeal. The association of artistic elements only used on movies and games are introduced in real engineering simulation creating a new way of understanding and interacting with this scientific data.
Dynamic Behaviour of Minimum Platforms Under Random Seas
Authors: Pilotto Micaela , Ronalds Beverley F.
Published: January 2009

This paper describes the dynamic response of minimum facilities with different structural configurations which are subjected to random seas. The finite element models are kept simple with the aim of focusing on the physics of the phenomena involved. The response is studied in terms of the dynamic amplification factor (DAF), representing the ratio between the dynamic and the static response. Two different formulations of the DAF under random seas are compared. The first is defined in terms of standard deviation (DAF1), the second in terms of the most probable maximum value (DAF2). Ringing is observed to be a relevant feature of the dynamic response and to affect primarily the braced monopod configurations. Ringing is detected using DAF2. The paper also addresses the importance of the kinematic representation above the still water level. Different methods of stretching the velocity field in the wave zone (delta, Wheeler and exponential stretching) are shown to have a significant impact on the dynamic response of the platforms.
Initial Development and Testing of an Adaptive Mission Planner for a Small Unmanned Underwater Vehicle
Authors: Arrieta Richard M. , Farrell Jay A. , Li Wei , Pang Shuo
Published: January 2009

An Adaptive Mission Planner (AMP) was developed for the REMUS Unmanned Underwater Vehicle (UUV) in order to have the vehicle react to real-time sensor data and alter course for the purpose of chemical plume tracing. In order for a UUV to track a plume autonomously, it must implement search strategies in an intelligent manner as dictated by environmental circumstances without human intervention. Throughout the mission, the UUV will combine the sensed flow and concentration information to construct a map of likely source or plume locations. This AMP has been designed and tested in simulation at the University of California, Riverside, and has now been installed on the SPAWARSYSCEN-SD REMUS UUV. This paper will describe the search strategies and initial field tests which use the AMP to break away from the vehicle’s pre-programmed missions. Two sets of experiments are described herein. The first uses bathymetry as the environmental driving input. The second uses chemical concentration as the primary input.
Further Investigation Into a Novel Concept for a Deformable Joint in Offshore Structures
Authors: Khonsari S. V. , England G. L. , Parvinnia S. M. H.
Published: January 2009

A new general semi-rigid beam-to-column connection for skeletal structures, also applicable to offshore platforms, was devised. In a previous paper (OMAE02-28264), the general features of this joint together with some proposed details for its use in fabricating new platforms, as well as retrofitting and repair of existing platforms, were introduced. Moreover, the results of some quasi-static tests on the ‘original’ version of the connection, in which the energy-dissipating elements (tubes) of the connection are laid in a parallel relation to the axis of bending, were reported. Here, in this paper, the results of recent experimental work on the ‘alternate’ version of the connection, in which the energy-dissipating sacrificial elements (tubes) are laid in a perpendicular relation to the axis of bending, are reported. The main differences between the behaviour of the two versions are the ‘rigidity,’ as well as the ‘strength’ of the tested specimens. However, the large ‘rotational capacity’ of the specimens is not jeopardized by the configuration of the connection, i.e. the relation between the axes of the tubes and that of bending. It is decided by the geometric parameters (sizes) of the connection. This can be designed independently of the joint strength and stiffness. The advantages of the joint, already observed in tests on the horizontally-laid-tubes version specimens (including the ability to contain damage, the ability to absorb and dissipate high amounts of energy, and the ability to deliver very large rotations), were also observed during the tests on the specimens of the vertically-laid-tubes version. Moreover, the fact that this version is also fabricated as a ‘separate entity,’ and thus can be easily subjected to the desired thermal cycle to remove the adverse effects of welding (in particular, embrittlement), makes it a suitable candidate for being used in ‘retrofitting’ and ‘repair’ of offshore platforms, where fatigue and the induced fracture are crucial factors.
Random Wave Response of Double Pendulum Articulated Off-Shore Tower
Authors: Islam Nazrul , Ahmad Suhail
Published: January 2009

Present study investigates the non-linear dynamic behavior of Double Hinged Articulated Tower (DHAT) under long crested random Sea and directional random sea. The non-linearities due to time wise variation of submergence, buoyancy, added mass, instantaneous tower orientation and resulting hydrodynamic loading have been taken into account for modeling the forcing functions of equation of motion which is derived by Largrangian approach. A long crested random sea has been modeled by Monte-Carlo Simulation using P-M spectrum. The non-linear equations of motion are solved by an iterative time integration scheme using Newmark’s β integration scheme. Various important parameters such as heel angles, deck displacements, base share for double hinged articulated tower under long and short crested random sea are compared and presented in the form of time-histories and their respective PSDFs. Statistical studies of random time histories have been carried out and important characteristics like mean, maxima, minima, standard deviations etc. have been analyzed. The dynamic behaviors have been investigated in detail in terms of various parametric combinations. Effect of current, and significant wave height are also studied. Sub and super harmonic excitations are highlighted through power spectra. A multi-hinged articulated tower is found to be economical and suitable for various offshore activities in adverse environmental and deep sea conditions.
Displacement and Pressure Transfer Between Structural and Fluid Meshes in Fluid-Structure Interaction
Authors: Huang L. L. , Riggs H. R.
Published: January 2009

Nonlinear, time-domain hydroelastic analysis of flexible offshore structures requires that the structural motion be transferred to the fluid model and the resulting fluid pressure at the fluid-structure interface be transferred from the fluid model to the structure. When the structural mesh and the fluid mesh describe two distinct three-dimensional surfaces, the transfer of displacement and pressure is both difficult and non-unique. In this paper, a new transfer strategy based on the variational-based smoothing element analysis (SEA) technique is presented. The displacement transfer uses the original formulation of the SEA method, although the application of the procedure to displacement transfer is new. For energy conservation during the reverse pressure transfer, the original functional in the SEA method is enhanced with a new term that attempts to conserve the work done by the hydrodynamic forces when obtaining the global structural nodal forces. To evaluate the transfer methodology, the hydrodynamic response of three rigid bodies are considered. Pressure contours, hydrodynamic coefficients, and motions that are calculated based on the data transferred with the proposed method are compared with the results that are obtained from standard rigid-body hydrodynamics theory that does not include a structural finite element model. The method is shown to work very well. In addition, it has general applicability and it can deal with relatively large geometric differences in the meshes.
Analysis of Hot Spot Stress and Alternative Structural Stress Methods
Authors: Dong P. , Hong J. K.
Published: January 2009

There is a growing need for robust finite element based fatigue assessment procedures for welded joints in offshore/marine structures. Although widely accepted in tubular structures, the applications of the conventional hot spot stress (HSS) procedures in plate structures have proven to be problematic in some joint types. There are a series of on-going international efforts that are intended to address some of the issues to improve the consistency of the HSS calculation procedures for plate structures. In this regard, alternative structural stress (SS) procedures that share some similarities to conventional HSS methods have been developed. The SS method has been shown to be effective in calculating structural stresses directly at failure locations such as at weld toes with minimum mesh-sensitivity. In this paper, detailed analysis and assessments of the conventional HSS and the alternative SS procedures are presented. Starting with the fundamental definitions of both HSS and SS parameters, the underlying mechanics associated with the two types of the stress analysis methods will be discussed by considering series of typical joint types, particularly on some of the important stress concentration characteristics that separate tubular joints from plate joints. Then, the necessary and sufficient conditions required for a stress definition relevant to fatigue and its calculation procedures will be demonstrated for both methods. Areas of concerns and improvements for both methods will be demonstrated by using a series of selected joint types typical of those in marine/offshore structures. Finally, the corresponding S-N data will be used to demonstrate the relative effectiveness of HSS and SS methods in consolidating the data from drastically different joint types into a single S-N curve.
Frequency Domain Analysis of a Deepwater Monobuoy and Its Mooring
Authors: Fernandes Antonio C. , Lima Andre´ L. S. , Oliveira Carlos A. F.
Published: January 2009

The paper addresses a CALM (catenary anchor leg mooring) monobuoy arrangement. There are several monobuoys installed in deeper waters from 400 m to 1000 m or more. This increases the mooring line effects on the first order monobuoy behavior, and unlike the much larger drilling and production platforms they cannot be neglected. As shown, in a frequency domain approach, it is possible to devise restoring force effects, damping effects and even inertial ones. Hence, the full understanding of the behavior is only reached if the mooring lines are properly considered. Model tests, an ad hoc linear diffraction theory computer program (ProMono) and a fully nonlinear time domain computer program are used in the analysis.
Refraction and Diffraction of Nonlinear Waves in Coastal Waters by the Level I Green-Naghdi Equations
Authors: Ertekin R. C. , Sundararaghavan H.
Published: January 2009

The Green-Naghdi (GN) equations are shallow-water wave equations which can be solved to predict the nonlinear and dispersive effects of water waves propagating in coastal waters. In this study, we formulate the Level I GN equations for variable bathymetry in 3-D, and numerically model the refraction-diffraction problem as an initial-boundary-value problem. A finite-difference model, in conjunction with elliptic grid-generation, is developed to solve the GN equations. Nonlinear wave propagation over a varying bathymetry is presented for solitary and cnoidal waves. A number of benchmark cases have been tested and compared with the available theoretical predictions. The results are presented and discussed to reveal the accuracy of the present model.
Dynamic Response of Shear-Deformable Axisymmetric Orthotropic Circular Plate Structures Solved by the DQEM and EDQ Based Time Integration Schemes
Authors: Chen Chang-New
Published: January 2009

The dynamic response of shear-deformable axisymmetric orthotropic circular plate structures is solved by using the DQEM to the spacial discretization and EDQ to the temporal discretization. In the DQEM discretization, DQ is used to define the discrete element model. Discrete dynamic equilibrium equations defined at interior nodes in all elements, transition conditions defined on the inter-element boundary of two adjacent elements and boundary conditions at the structural boundary form a dynamic equation system at a specified time stage. The dynamic equilibrium equation system is solved by the direct time integration schemes of time-element by time-element method and stages by stages method which are developed by using EDQ and DQ. Numerical results obtained by the developed numerical algorithms are presented. They demonstrate the developed numerical solution procedure.
Evaluation and Prospect on Comprehensive Fishing-Village Development Project in the Republic of Korea
Authors: Kim Jong Deog , Kim Sung Gwi
Published: January 2009

In terms of fishery policy in the Republic of Korea (hereinafter Korea), efficient resources management and the improvement of the infrastructure have been main targets of the industrial policy for a long time. On the other hand, fishermen’s society has maintained an exclusive and conservative socio-economic structure based on fishery cooperatives. However, with the advent of the new global trade order, the so-called Uruguay Round (UR), Korea’s fishery policy was requested to change the existing paradigm. To address this change in circumstances, the Korea government has begun to emphasize a people-oriented policy, for example, welfare, safety, education and diversified income sources, etc., instead of a production-oriented policy. In particular, the new law — Act on Special Tax for Rural Development — was enacted in 1994 to provide financial funding for various policy changes, including the implementation of the Comprehensive Fishing-village Development Project (hereinafter CFDP) as a new measure to address fishermen’s difficulties originating from the new trade round. CFDP aimed at raising the competitiveness of the fishery and the improvement of the quality of life in fishing-villages. The present study was conducted as an interim evaluation of the socio-economic effects of the projects implemented in the early stage of the CFDP, from 1994 to 1998.
Flexible Pipe Integrity Management
Authors: Souza Luiz , Filho Salvador , Carpigiani Marcos , Freitas Jeter
Published: January 2009

At present, flexible pipes are used worldwide to conduct several fluids within the offshore oil production industry. These flexible pipes are complex composite structures made up of several plastic and steel layers. They are intended to work for a long period of time, something around 20 years. Although the flexible pipes behavior is satisfactory in most applications, they are susceptible to simple damages, for example on the external sheath, which much reduces their service life. The offshore inspection activities are extremely expensive and, given that, these activities need to be very well oriented in order to be effective. This paper describes the Risk Based Inspection Methodology, which is a helpful applicable tool in the integrity management of several flexible pipe systems, allowing to concentrate the efforts where they are really needed. This methodology may be used by the oil companies to reduce overall costs and enhance safety and integrity of the production systems.
Determination of the Collapse and Propagation Pressure of Ultra-Deepwater Pipelines
Authors: Toscano Rita G. , Timms Chris M. , Dvorkin Eduardo N. , DeGeer Duane D.
Published: January 2009

In the design of ultra-deepwater steel pipelines, it is important to be able to determine the pipe behaviour while subjected to external pressure and bending. In many cases, the ultra-deepwater lay process, where these high loads exist, governs the structural design of the pipeline. Much work has been performed in this area, and it is generally recognized that there is a lack of test data on full-scale samples of line pipe from which analyses can be accurately benchmarked. This paper presents the results of a nil-scale test program and finite element analyses performed on seamless steel line pipe samples intended for ultra-deepwater applications. The work involved obtaining full-scale test data and further enhancing existing finite element analysis models to accurately predict the collapse and post-collapse response of ultra-deepwater pipelines. The work and results represent a continuing effort aimed at understanding the behaviour of pipes subjected to external pressure and bending, accounting for the numerous variables influencing pipeline collapse, and predicting collapse and post-collapse behaviour with increasing confidence. The test program was performed at C-FER Technologies (C-FER), Canada, with the analyses undertaken by the Center for Industrial Research (CINI), Argentina. The results of this work have demonstrated very good agreement between the finite element predictions and the laboratory observations. This allows increased confidence in using the finite element models to predict collapse and post-collapse behaviour of pipelines subject to external pressure and bending.
Assessment of Fatigue Safety Factors for Deep-Water Risers in Relation to VIV
Authors: Leira Bernt J. , Meling Trond Stokka , Larsen Carl M. , Berntsen Vidar , Stahl Bernie , Trim Andrew
Published: January 2009

Safety factors required to control fatigue damage of deepwater metallic risers caused by Vortex-Induced Vibration (VIV) are considered. Four different riser configurations are studied: • Case I and II: Vertical tensioned 12” risers suspended from a spar buoy at water depths of 500m and 1500m. • Case III and IV: Steel catenary risers suspended from a spar buoy, both at 1000m. For Case III, the riser diameter is 12”, while for Case IV it is 30”. For each riser configuration, relevant design and analysis parameters which are subject to uncertainty are identified. For these quantities, random variables are established including model uncertainties. Subsequently, repeated analyses of fatigue damage are performed by varying the input parameters within representative intervals. The results are applied to fit analytical expressions (i.e., so-called response surfaces) utilized to describe the limit state function and to develop the probabilistic model for reliability analysis of the risers. By combining the random variables for the input parameters with the results from the parameter variations, the relationship between the fatigue safety factor and the failure probability is established for each riser configuration.
An Assessment of Response-Surfaces for Estimation of Fatigue Damage and Extreme Response Due to Environmental Loads
Authors: Leira Bernt J. , Holma˚s Tore , Herfjord Kjell
Published: January 2009

For marine structures subjected to environmental loads (i.e. waves, current, wind), the fatigue damage and long-term response characteristics can frequenlty expressed in terms of the environmental parameters by polynomial response surfaces. For both types of “response”, an integration across the range of variation for all the environmental parameters is required. The location of the intervals which give rise to the dominant contribution to these integrals is studied. Convergence studies are performed by applying response surfaces of increasing order, from linear to cubic expressions. In addition, response surfaces with lower cut-off limits at specific values for the environmental parameters are also investigated. Having obtained general expressions on non-dimensional form, various examples which correspond to specific response quantities for marine structures are considered. Typical values for the polynomial coefficients, and for the statistical distributions representing the environmental parameters, are applied. Convergence studies are subsequently performed for the particular example response quantities which are considered in order to make comparison with the general formulation. For the extreme response, the application of “extreme contours” obtained from the statistical distributions of the environmental parameters in combination with the response surface is explored.