bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave Loads on Floaters of Aquaculture Plants
Authors: Kristiansen David , Faltinsen Odd M.
Published: July 2009

This paper addresses wave loads on horizontal cylinders in the free surface zone by means of model tests and numerical simulations. This has relevance for the design of floating fish farms at exposed locations. Two model geometries were tested, where two-dimensional flow conditions were sought. The cylinders were fixed and exposed to regular wave trains. Wave overtopping the models were observed. A two-dimensional Numerical Wave Tank (NWT) for wave load computations is described. The NWT is based on the finite difference method and solves the incompressible Navier-Stokes equations on a non-uniform Cartesian staggered grid. The advection term is treated separately by the CIP (Constrained Interpolation Profile) method. A fractional and validation of the NWT is emphasized. Numerical results from simulations with the same physical parameters as in the model tests are performed for comparison. Deviations are discussed.
Reservoir Souring Modelling, Prediction and Mitigation
Authors: Evans Paul
Published: July 2009

The prediction of reservoir souring due to the activity of sulphate-reducing bacteria (SRB) during water injection is an important consideration in material selection for wells and production facilities. A number of reservoir souring models have been developed in the past 16 years or so, with the objective of predicting the timing and magnitude of H2S production. The results of the reservoir souring models are dependent on a number of reservoir geometry, geochemical, microbiological and reservoir geology parameters. For example, the SRB activity is dependent on the availability of essential nutrients such as sulphate and dissolved hydrocarbons in the injection and formation waters. Environmental parameters such as temperature and pressure control in which parts of the reservoir SRB can be active. Water flow path and extent of water breakthrough has a major impact on H2S production. Very low reservoir permeabilities will restrict the movement of SRB into the rock matrix and certain minerals have the ability to scavenge H2S within the reservoir. All of these parameters must be accounted for in a reservoir souring simulation, and this requires the cooperation of reservoir engineers, geologists, production chemists and facilities engineers. Several techniques have been employed in the oil industry to try to control the generation of H2S within the reservoir. These include the application of biocides to control SRB activity, the injection of nitrate to stimulate other bacterial populations to out compete SRB for available food sources and the use of sulphate removal technologies to minimize sulphide production.
Effective Bending Stiffness of an Unbonded Flexible Riser
Authors: Zhang John , Tan Zhimin , Sheldrake Terry
Published: July 2009

A simplified model is proposed for describing the hysteresis behaviour of an unbonded flexible pipe during bending. The model has been developed based on available bending test data and numerical studies. Using the model, a simplified hysteresis loop for a given flexible pipe under specified loading conditions can be evaluated. With the simplified hysteresis loop, the global dynamic analysis and the fatigue life analysis of a flexible riser can be conducted more efficiently without loss of accuracy.
Analysis of the Flow Around a Manoeuvring VLCC
Authors: Muscari Roberto , Broglia Riccardo , Di Mascio Andrea
Published: July 2009

This work describes the numerical simulation of a turning circle manoeuvre performed by the MOERI KVLCC2 induced by the rotation of the rudder. To this purpose, the Navier-Stokes equations are integrated, the hydrodynamical forces acting on the hull are computed and the hull is moved at each time step according to the rigid body equations. Because of the scarceness of experimental results for this kind of simulations, the validation of the proposed method is postponed to the oral presentation when the data from the SIMMAN 2008 Workshop (http://www.simman2008.dk/) will be available.
Human Impacts on the Hydrology in Pearl River Delta, China
Authors: Zhang Wei , Hao Jialing
Published: July 2009

The Pearl River Delta (PRD) lies in the south of GuangDong province in China. It is the river networks area of the lower reaches of MaKou of West River, Sanshui of North River and ShiLong of Dongjiang River. Over the last 20 years, in order to keep sustainable development of economy, many regulations engineering to improve grade of channel from river networks to estuary was implemented in 1990’s. At the same time, artificial sand excavation reached the peak level. These human activities impacted the hydrodynamic greatly than natural evolution. As a result, the morphology and hydrology of the PRD water system has been predominantly dictated by those human activities. In this paper, based on the Saint-Venant equations, a numerical model of junction-river course for the whole PRD was established by using the junction-control methods for water level. First, the river networks in the PRD are schematized as 340 main river courses, 216 nodes and 1850 cross sections. The areas of this river networks are approximately 2000km2, and the total river length is more than 1600km., second, utilizing the transforms of the single river finite-difference equations and the mass and energy conservation at the river junction, the control equations for all junctions’ water level can be written in matrix notation. The water level at all junctions are obtained by solving the irregular spare matrix equations, finally, the water level at all single river sections are gotten by the solution algorithm for the single river unsteady flow. After calibration, simulation under different topographical condition in 1990 and in 2005 respectively was made. This paper put much emphasis on comparison changes of the hydrodynamic condition in PRD in recent 20 years by numerical model and observation data. Research result shows that frequent human activities caused the change of topographical; which result in changes of the hydrodynamic, such as the tide range in PRD shows abrupt shift and the divided flow ratio between various water courses change. More specifically, the average annual tide range at Makou was 0.32m in 1990, however; it was 0.55m in 2005. Meanwhile, the dramatic change of hydrodynamic in PRD directly results in stronger saline intrusion in recent years.
Plunging Wave Impact on a Wall
Authors: Shu Jian-Jun
Published: July 2009

The intention of this paper is to study impact force of an oblique-angled slamming wave acting on a rigid wall. In the present study the analytical approach is pursued based on a technique proposed by the author. A nonlinear theory in the context of potential flow is presented for determining accurately the free-surface profiles immediately after an oblique breaking wave impingement on the rigid vertical wall that suddenly starts from rest. The small-time expansion is taken as far as necessary to include the accelerating effect. The analytical solutions for the free-surface elevation are derived up to the third order. The results derived in this paper are of particular interest to the marine and offshore engineering industries, which will find the information useful for the design of ships, coastal and offshore.
Seabed Shear Stress Spectrum for Very Rough Beds
Authors: Myrhaug Dag , Holmedal Lars Erik
Published: July 2009

The spectrum of seabed shear stresses at beds with large roughness beneath ocean surface waves in finite water depth is derived by using the wave friction factor for large roughness. It is expressed in terms of the transfer function between the waves at the surface and the shear stress at the bed, and the wave spectrum in finite water depth, which is obtained by multiplying the deep water wave spectrum with a depth correction factor. The seabed shear stress spectrum for laminar flow, which is of practical interest for flow over muds, is also given as a reference case. Examples are included to illustrate the applicability of the seabed shear stress spectrum for practical purposes using data typical for field conditions, both for very rough beds and mud beds.
Evaluation of Welding Flaws Under Ratcheting Fatigue
Authors: Gioielli Paulo , Buitrago Jaime , Kan Wan , Weir Michael , Chell Graham , Hudak Steve
Published: July 2009

Hydrocarbon-carrying lines can be subjected to cyclic loads superimposed on monotonically increasing mean strains well into the plastic domain, resulting in tearing and tearing fatigue of initial welding flaws. This combined demand is referred to here as ratcheting fatigue. Examples of these loads are frost-heave in pipelines and thermal cycling of flowlines. This paper presents the experimental verification of a fracture mechanics model of monotonic and cyclic crack extension under ratcheting fatigue loads and its calibration to small-scale tests. The model is an extension of one currently used to predict tearing and tear-fatigue due to reeling. Crack driving forces (J-solutions) under load- and displacement-control conditions were derived and used with the model to predict test results. A total of 24 single-edge notched bend (SEN-B) specimens, taken from a welded riser, were tested for crack extension under combined monotonic and cyclic loads. Comparisons of predicted to measured fatigue crack-growth rates, and alternatively cyclic J-R curves, provide quantitative and qualitative validation of the model. However, calibration to large–scale tests are needed before the model can be used for design. ExxonMobil has already completed the first set of large-scale pipe tests under ratcheting fatigue loading, including internal pressure.
Effects of Wave Drift Forces on Maneuvering of Ship
Authors: Kinoshita Takeshi , Bao Weiguang , Yoshida Motoki , Nihei Yasunori , Xu Yongze , Itakura Hiroshi
Published: July 2009

The dynamic positioning system of floating ocean structures requires hydrodynamic force derivatives to construct an accurate maneuvering model. In a severe sea state, the effects of ambient wave field on the maneuvering properties are not negligible. To investigate wave drift forces affecting on maneuvering of a ship relating to dynamic positioning system, an innovative model test, i.e. the Planer Motion Mechanism (PMM) test in waves is discussed in the present paper. Meanwhile, a theory to evaluate wave drift force including wave drift damping and wave drift added mass is summarized. Some examples of experiments done in Ocean Engineering Wave Basin of Institute of Industrial Science, University of Tokyo are presented and compared with calculated results based on the above theory.
Hydroelastic Analysis of a Hybrid-Type VLFS in Water of Variable Depth
Authors: Utsunomiya Tomoaki , Watanabe Eiichi , Noguchi Takatoshi , Yamamoto Syuji , Kusaka Tadasu , Ogamo Tatsunori
Published: July 2009

This paper presents a hydroelastic analysis of a hybrid-type VLFS in variable sea depth. The VLFS model is the prototype of a floating runway with dimension 3120m in length, 524m in width, 1.5m in draft for pontoon part and 11.5m in draft for semisubmersible part. A three dimensional Finite Element model using beams and quadrilateral plate elements are used in the hydroelastic analysis in order to obtain an accurate approximation. An equivalent plate model having the same eigenfrequencies and eigenmodes in air is also used in the analysis. The results using the 3D model and the plate model have been compared and their agreement is satisfying. In order to examine the variable sea depth at the expected site, the hydroelastic analysis is carried out for a flat bottom, a constant slope, and a variable sea depth case. The effect of variable sea depth is found to be significant.
Numerical Simulation on Motion Responses of the Tsunami-Induced Grounding on a Wharf of Floating Structures Using the MPS Method
Authors: Masuda Koichi , Ikoma Tomoki , Masuda Mitsuhiro , Suzuki Yuta
Published: July 2009

The present paper describes the application of the moving particle semi-implicit method to a prediction of tsunami-induced grounding of floating structures in the vicinity of wharfs. Effectiveness of the application is verified. Solitary wave have been applied to simulated tsunamis in numerical simulation and to the model experiments. A pontoon type floating body has been used to floating structures in numerical simulations using the MPS method. The present numerical results have been compared with the experimental results and the applicability of MPS method has been discussed. Further, after the grounding, the characteristics of gliding distance of floating body on the wharf have been discussed.
Dependence of Shape Parameter of Weibull Distribution on Wave Spectral Width and Nonlinearity
Authors: Li Changliang , Liang Bingchen , Zhao Lin
Published: July 2009

In practice, the wave height distribution associated with an irregular wave train is always mathematically modeled as a Rayleigh distribution. However, the realistic ocean wave height distribution might deviate from a Rayleigh distribution. The present study demonstrates that a better mathematical model for wave height distribution under realistic ocean environment is a Weibull distribution. In comparison with a Rayleigh distribution, a Weibull distribution has the flexibility on choosing its “shape parameter”. According to the nonlinear Monte Carlo simulations, this study investigates the nonlinearity and spectral width effects on the shape parameter for the Weibull wave height distribution. A new empirical formula for calculating the shape parameter is proposed, which can be used easily in application.
Explicit and Implicit Integration Algorithms for an Elastoplastic Pipe-Soil Interaction Macroelement Model
Authors: Tian Yinghui , Cassidy Mark J.
Published: July 2009

This paper presents the numerical formulation of an elastoplastic force-resultant model to numerically simulate the interaction of a pipe with the soil. This approach, which accounts for the load-displacement behaviour of the pipe-soil system on a macroelement level, is becoming increasingly popular in offshore engineering. The model consists of a yield surface, a non-associated flow rule, an isotropic hardening law and a description of purely elastic behaviour. It can be used to predict the behavior of one segment of pipe or numerous models can be attached to structural finite elements as nodal point elements. The latter allows the practical analysis of long pipelines. Further, by removing a number of macroelements from the pipeline, the effect of free span can be studied. To numerically incorporate large numbers of macroelements into a structural analysis, efficient and robust integration algorithms are essential. The use of both explicit and implicit integration algorithms are explored in this paper. In the explicit algorithm, the Euler forward integration scheme is adopted to achieve the real force state incrementally for each substep. On the other hand, the Euler backward integration scheme is adopted in the implicit algorithm. In this case the load state is iteratively “returned” back to the yield surface according to the end of the total displacement increment. Illustrative calculation examples are provided in this paper to demonstrate and compare the performance of the suggested algorithms.
Derivation or Ship System Safety Criteria by Means of Risk-Based Ship System Safety Analysis
Authors: Ru¨de Erich , Hamann Rainer
Published: July 2009

Nowadays an increasing popularity of alternative designs can be observed challenging the IMO Regulations of SOLAS (International Convention for the Safety Of Life At Sea). Examples are passenger ships with larger main vertical zones, novel types of survival crafts and new materials. This desire for innovative solutions combined with the society’s need for increasingly safer transport is expected to be satisfied by risk-based ship design and approval. The process of alternative ship design and arrangements, as described in MSC/Circ.1002 and MSC.1/Circ.1212, requires a risk analysis to demonstrate that the risk contribution of the novel design is less or equal to the present design. Thus the application of this process can also be regarded as risk-based design. The application of risk-based design is driven by the need for continuous improvement of the efficiency leading to lower costs for design, manufacturing or operation, because it offers the required frame for the development of new innovative solutions. IACS defines safety as absence of unacceptable levels of risk to life, limb and health. Risk is defined as a measure of likelihood that an undesirable event will occur together with a measure of the resulting consequence within a specified time, i.e., the combination of the frequency or probability and the severity of the consequence. Risk-based design involves risk assessment and risk evaluation criteria that can be defined, for instance, on basis of historical data or the ALARP process (As Low As Reasonably Practicable) combined with cost-benefit analysis. In this paper the definition of a risk evaluation criterion for systems by means of ALARP and cost-benefit analysis is presented and illustrated by a sample design of a ship fuel oil system. The risk contribution tree used for the analysis is composed of fault trees and event trees. A cost-benefit analysis is applied to establish a target system risk criterion in form of a target system failure probability. Problems related to the discrete structure of systems are discussed. The work shows that different risk analysis methods are required to describe the escalation chain from a component failure to a potential accident and its consequences.
Recommended Design Fatigue Factors for Reassessment of Piles Subjected to Dynamic Actions From Driving
Authors: Lotsberg Inge , Sigurdsson Gudfinnur , Arnesen Knut , Hall Michael E.
Published: July 2009

Calculated probabilities of fatigue failure depend on the analysis procedure used for design. Calculated probabilities of a fatigue failure also depend on long term stress ranges due to loading and uncertainties associated with this. In order to ensure consistent safety level for assessment of fatigue failure the Design Fatigue Factors (DFFs) to be used for fatigue design should be dependent on the analysis procedure and premises used. In the present paper an assessment of appropriate DFFs for piles subjected to dynamic actions from pile driving has been performed by probabilistic analysis based on: • Uncertainty with respect to dynamic cyclic stress during pile driving. • Fatigue capacity of circumferential welds in piles. Accumulated probabilities of fatigue failures in pile butt welds are presented. An assessment of uncertainties involved in calculation of stress ranges during pile driving has been performed. It is shown that the uncertainty in loading when driving records are known is lower than that estimated on the basis of soil data. Thus, in order to obtain consistent safety levels, different DFFs should be used when calculated stress ranges are derived based on soil data only, as compared with the actual stress ranges and number of blows determined from driving records. The results from probabilistic analyses together with recommended Design Fatigue Factors are presented in this paper.
Semi Automatic Failure Analysis Based on Simulation Models
Authors: Hamann Rainer , Uhlig Andreas , Papadopoulos Yiannis , Ru¨de Erich , Gra¨tz Uwe , Walker Martin , Lien Rune
Published: July 2009

Classical risk assessment and risk management which is gaining importance in many industries is usually based on well defined processes and uses techniques like FTA and FMEA. However, classical risk analysis techniques like FTA and FMEA should ideally be automated, at least to some extent and without loss of effectiveness, to enable fast and cost effective iterations of system modelling and risk analysis that can meet the tight cost and time constraints of most offshore projects. This paper is focused on the presentation of a new concept and tool extension for model-based synthesis of fault trees and FMEAs in which these failure analyses are automatically constructed from engineering design models, e.g. simulation models that have been augmented with information about the local propagation of failures. The simulation model is developed in the commercial system modelling tool SimulationX. The proposed process enables the automatic generation of both fault trees and FMEA tables in a single run of the tool, allowing the FMEA and fault trees to share failure data and allowing the FMEA to include failures caused by multiple basic events. As it is a largely automated process, it could be easily iterated to enable the continuous assessment of evolving designs. It provides an automatic generation of fault trees and FMEA tables for multiple top events in a single run of the tool. The potential benefits from application of this technique and tool are substantial and include simplifying the analysis, easing the examination of effects of design modifications on safety and keeping the safety analyses consistent with the design. Furthermore, the presented approach combines the benefits of simulation and risk analysis in one tool. The benefits of this approach are demonstrated by the example of a blow out preventer for a subsea installation valve.
Scaled Boundary FEM Solution of Wave Diffraction by a Square Caisson
Authors: Song Hao , Tao Longbin
Published: July 2009

In this paper, the scaled boundary finite-element method (SBFEM) proposed for interaction of wave and circular cylinder [Tao et al, 2007] is modified and applied to wave diffraction by a vertical square caisson. By introducing a virtual circular cylinder surrounding the square caisson, the whole fluid domain is divided into one unbounded subdomain and four bounded subdomins. The corresponding boundary value problems in bounded and unbounded domains are solved by the SBFEM using different base solutions. Comparisons to the previous BEM solutions demonstrate the excellent computation accuracy and efficiency of the present SBFEM approach, as well as the benefit of not suffering from the difficulties of irregular frequency and singularity problems, which are often encountered by BEM. The method can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.
Ice Tank Testing of a Surface Buoy for Arctic Conditions
Authors: Dalane Oddgeir , Gudmestad Ove Tobias , Lo̸set Sveinung , Amdahl Jo̸rgen , Hilde`n Tor Erik , Fjell Knut Harry
Published: July 2009

A moored Shallow Draught Buoy (SDB) for potential operations in Arctic waters was tested during the summer of 2006 in the model laboratory basin at the Hamburg Ship Model Basin (HSVA) in Hamburg. The conceptual design of this buoy was based on the design of the Kulluk exploration vessel which operated in the Beaufort Sea in the 1980’s and early 1990’s. The concept was tested in ice conditions representing level ice, multiyear ice and ridged ice, where the ice thickness, ice drift velocity and flexural strength were varied in the different test runs. Moored structures are believed to be favourable in deep waters with ice present, but there exist insufficient information and data about the actions on and behaviour of moored floating structures in ice to support this. The purpose of the present paper is to evaluate the model test results and look at the dynamic ice loading and response of the structure. The ice forces on the structure were calculated from the structure’s response and response power density spectra were used to evaluate the periodic forces and displacements. Based on the analysis of the test data, an increased understanding of the behaviour of the surface buoy is presented.
The WAG Squall Measurement System
Authors: Jeans Gus , Redford Stephen , Bellamy Ian , Mundy Richard
Published: July 2009

Squalls control design wind conditions offshore West Africa, where the wind regime is otherwise relatively benign. The West Africa Gust (WAG) Joint Industry Project was initiated in 2004 to make best use of available industry data for characterisation of squalls in engineering design. The WAG phase one report highlighted the need for further measurement to address uncertainties in the horizontal and vertical structure of squall winds. This paper describes the resulting measurement system installed on a platform offshore West Africa.
Wave Response of a Semisubmersible Floating Structure Model With Mechanical Connectors
Authors: Watanabe Yoshiyasu , Yoshida Koichiro
Published: July 2009

It is desired instead of welding to develop a mechanical connector, which may work well to connect two units at the site in spite of circumstances of some extent of relative motions between two units caused by waves. One of the authors proposed a new type of mechanical connector, which is based on an idea of three bodies problem instead of usual mechanical connectors (two bodies problem). In this paper, wave exciting tests of a semisubmersible floating structure model with the proposed mechanical connectors of 1/100 scale and the numerical analysis using hydroelastic response analysis program VODAC are carried out and wave response characteristics of the semisubmersible floating structure model with the mechanical connectors and its feasibility are reported.
Advanced Pipeline Trawl Gear Impact Design
Authors: Igland Ragnar T. , So̸reide Tore
Published: July 2009

Non-linear dynamic finite element analysis for the interference between clump weight and pipeline on seabed is performed using ANSYS software package, Ref /1/. Output from the analysis is the pull-over force magnitude, as well as shape and duration of impact on pipeline from the clump weight. Two pipelines sizes are analysed for trawl pull-over, the 10" and 12" pipelines laying on seabed. Small scale tests have been used to verify the FE model. The dynamic behaviour during impact testing is fairly well simulated by FE analysis scheme chosen. The results from the FE analysis are compared with the recommended practise outlined by DNV-RP-F111. Realistic trawl pull-over loads are established using actual stiffness of the pipeline and the pipe-soil interaction. The reduced trawl loads and the effect of pipe-soil interaction lead to reduced load effects and will avoid a conservative design and reduce the intervention costs.
A Study on Wave Response and Evaluation of Habitability of Floating Restaurant
Authors: Eto Hiroaki , Saijo Osamu , Maruyoshi Koichi
Published: July 2009

Since Japan is limited in area, the effective ocean space development is very important and urgent subject. Concerning a research and development of effective ocean space utilization, the MEGA-FLOAT was one of the most famous projects in Japan that had the purpose of a floating airport construction, and the numerous R & D were conducted aiming at actual construction and those results were reported in respect of conceptual design, construction method, fluid analysis, structural dynamic analysis, environment issue etc. However, the end was faced without achieving it, it can be said that the effect is large. After the end of that project, the realistic, small or medium size structure began to be paid to attention. As the good example of such a kind floating structure, floating pier and disaster prevention base having an advantage against an earthquake, floating restaurant etc. were constructed shown in Figure 1. In this paper, assuming the small size floating restaurant, the wave response analysis was studied, and the habitability of that structure was evaluated from the response calculation results. Concretely, the floating base part; barge type of the restaurant building was designed by the Class NK (Rules and Guidance for the survey and construction of steel ships, Part Q Steel barges). The calculation model consists of a three-story building and the base, that floating artificial base supporting the building was assumed by the elastic plate structural system, and also that building was of the frame structure system. In order to structural analysis, the restaurant model of two different structural systems was united into one body system. In this paper, it is called the hybrid structural system. Fluid effect was analyzed as the fluid-structural interaction problem. Concretely, the Boundary Integral Equation Method (BIEM) was used here, and the wave response calculation was demonstrated by that forces. The evaluation of habitability of the restaurant in vertical and horizontal motion was examined by the diagram proposed from our research results.
Retrofittable Stress Measurement Instruments for Deepwater Risers and Flowlines
Authors: Roberts Damon
Published: July 2009

Growth in the need for integrity management of deepwater assets has stimulated new approaches to integrity monitoring to be adopted by the industry. Subsea fibre optic stress sensors have been widely deployed on both shallow water and deepwater risers due to their high sensitivity, reliable operation and ease of installation. The instruments are usually attached on deck as the riser or flowline is deployed, however recently an increasing number of instruments have been retrofitted. The first ever retrofit deployment of a subsea fibre optic stress measurement instrument was to monitor the integrity of a flex joint on a deepwater export riser in the Gulf of Mexico. Another project saw bending moment and axial load sensors retrofitted to SCR wet spool pieces on a deepwater project in GoM. Further systems designed and manufactured and awaiting installation include a system for monitoring cyclic stresses in a flexible riser at the hang off, a system for monitoring fatigue accumulation in a conductor and a system to determine the location of a wax plug on a rigid flowline. This paper will present details of the above systems and will discuss their design, manufacture and varying installation methods together with test data and field measurements.
Experimental Study Into Vortex Induced Motion Response of Semi Submersibles With Square Columns
Authors: Rijken Oriol , Leverette Steven
Published: July 2009

Vortex Induced Motion (VIM) of a Deep Draft Semi® with four square columns has been observed in model tests and in a prototype configuration. The flow field around the columns causes the vessel to oscillate along one of the vessel’s main diagonals under particular conditions. The observations and conclusions of three series of VIM model programs are combined in this report. Each test program was executed with a unique objective in mind and each setup was unique. Many similarities in response characteristics have been identified. Some of the differences in observed response are identified and discussed. A discussion is provided regarding the scaling of VIM problems, and the importance of the Reynolds number under model test conditions is discussed. The VIM of a typical Gulf of Mexico Deep Draft Semi® may affect the fatigue life of the mooring system and risers. A formulation is developed that predicts the distribution of VIM amplitudes which then can be used to estimate VIM induced fatigue damage. Observations and conclusions are provided of several experiments where VIM response was evaluated in the presence of a fatigue sea state and for a system with increased sway damping.
Structural Integrity Monitoring: Review and Appraisal of Current Technologies for Offshore Applications
Authors: May P. , Sanderson D. , Sharp J. V. , Stacey A.
Published: July 2009

The use of structural integrity monitoring techniques on offshore installations provides the potential to reduce the risk of structural failure. The Health and Safety Executive’s (HSE’s) Offshore Division has funded a review of relevant technologies in structural integrity monitoring with potential application to offshore installations as well as practical offshore experience with structural integrity monitoring. The purpose of the study was to identify current capabilities of structural integrity monitoring techniques for structural integrity management of offshore installations (i.e. offshore jackets and semi-submersible structures used for drilling and or production operations but excluding FPSOs), to identify limitations in current approaches and identify areas for further development, to identify opportunities for technology transfer from other industries and to review and assess key research and development including current initiatives. The key structural integrity monitoring methods relevant to offshore structures were reviewed. It was found that offshore experience of structural integrity monitoring is limited to date and that all current systems are for bespoke applications. Current codes and standards refer in a limited sense to the use of structural integrity monitoring and this may influence the limited take up to date of this technology. However, there is a regulatory requirement for leak detection in ageing semi-subs as a recent introduction to DNV classification rules OSS-101 [1].
Repair Techniques for Flexible Pipe External Sheath
Authors: Netto T. A. , Touc¸a J. M. , Ferreira M. , Gonc¸alez V. , Marnet R.
Published: July 2009

During installation or service, the external sheath of flexible pipes can suffer damages that may result in loss of sealing and exposure of the annular region to the external environment. Additionally, visual inspection of the armor layers is sometimes necessary to assess their structural integrity. Such procedure requires cutting out a small segment (window) of the external sheath. One of the most effective inspection techniques to detect problems in the topside relief valves, damages on the external sheath, or pressure barrier failure is the surface monitoring of the pressure in the annular region. Therefore, in the event of sheath damage or inspection windows, in situ repair techniques that guarantee the recovery of its sealing properties are important, particularly in the regions above sea level and water depths usually up to 30 meters. When the pipes are below this level, repairs are in general done on board of an installation vessel. Due to the inherent complexities of each region, specific repair techniques have been developed by PETROBRAS to date. Nevertheless, these techniques do not guarantee the annular space sealing, therefore hampering pressure monitoring. The objective of this work was to develop an external sheath repair technique using light, resistant, and easy-to-install materials for the areas above sea level and small depths (up to 30 m) capable to provide the necessary sealing for annular space monitoring.
Collapse Mechanism of Unbounded Metal-Composite Pipes Under Hydrostatic Pressure
Authors: Pasqualino Ilson Paranhos , Netto Flavio Antoun , Netto Theodoro Antoun
Published: July 2009

Metal-composite pipes are feasible alternatives for deepwater applications where thermal insulation and structural behavior requirements must be met. They are composed of an inner metal pipe and an outer structural composite layer which act in combination to provide excellent structural strength and additional thermal insulation. In this work, the mechanical behavior of such pipes under external pressure is investigated through numerical analyses and experimental tests. Small scale models were tested under external pressure to calibrate a finite element based numerical model. The FE model incorporates nonlinear kinematics, progressive failure analyses of the composite layer, and metal elastic-plastic behavior. Unbounded interface between metal and composite was assumed through frictionless surface-based contact model in other to obtain a conservative estimate of the metal-composite pipe performance under external pressure.
Validation Study of MPS (Moving Particle Semi-Implicit Method) for Sloshing and Damage Stability Analysis
Authors: Rueda Guilherme E. , Tsukamoto Ma´rcio Michiharu , Medeiros Higor F. , Yee Cheng Liang , Nishimoto Kazuo
Published: July 2009

The aim of this paper is to present validation studies of a CFD code based on MPS (Moving Particle Semi-implicit Method). In MPS method the fluid is represented by particles, and the particle interactions are governed by continuity and Navier-Stokes equations. It is a meshless method to simulate incompressible flow and it is able to simulate large surface distortion, fluid fragmentation and non-linear dynamics. For the validation studies, two cases with complex hydrodynamic phenomena were selected for experimental measurements in towing tank. The first one is the dynamics of a floating body in waves with an internal tank partial filled with water. In this way sloshing effects on the motion of the model can be evaluated. Usually, dynamics of the floating body and sloshing are calculated separately, by neglecting their coupling effects; the body’s motion is determined without sloshing and that motion is used to excite the liquid tank. Since the sloshing generates forces and moments, which may change the movement of the hull, sloshing forces and moments may act as a roll absorption device or can enlarger it. In MPS this coupled phenomena can be easily simulated, just by using particles representing water of the internal tank, water of the towing tank and structural particles representing the hull, the walls and the wave maker. The second phenomenon is the motions of a damaged hull from the moment soon after suffering damage until reaches the equilibrium position. This is an initial step of a validation study of the motion of a damage hull in waves, which will be compared with physical experiments. The comparisons between the numerical results obtained by the MPS with the experimental and theoretical ones show very good agreement, reinforcing the potential of MPS.
Anaylsis of Ductile Fracture Initiation in Corroded Plates
Authors: Yu Weiwei , Wang Ge , Chung Hyun , Karr Dale G.
Published: July 2009

Corrosion of marine structures often compromises structural integrity by reducing fracture elongation and strength, yield and ultimate strength, and fatigue life. When localized or pitting corrosion occurs, strength reduction can be difficult to establish because the effects of uneven surfaces affect the stress fields and failure modes of the structure. We examine in this paper the effects of corrosion on the ductile fracture of steel plating. Defects in material are known to affect the strain-to-failure of ductile metals. Such effects are included in the analyses presented for thin plates subjected to axial stress with local geometric defects caused by corrosion. A strain-to-failure criterion is used for predicting ductile fracture of the plating. Results of fracture strain reduction for particular corrosion states are presented for common ship hull steel. The reduction in strain to failure is shown to be dependent on the size of the elements considered as well as the pitted plate geometry.
Numerical Simulation of a Pipeline Installation Procedure at the Negro River
Authors: da Silva Danilo Machado Lawinscky , Correˆa Fabri´cio Nogueira , Jacob Breno Pinheiro , Torres Fernando Gomes da Silva , de Medeiros Antonio Roberto
Published: July 2009

The installation of pipelines is among the most challenging offshore operations. Conventional offshore pipeline installation operations in Brazil have been performed in an S-Lay procedure employing the BGL-1 barge, owned by Petrobras. The BGL-1 is a second generation lay barge and performs installation operations by moving forward using its own mooring lines. The objective of this work is to present the numerical simulation of a pipeline installation operation performed at a particular scenario, Negro river in the Amazon forest. The high current velocity, very irregular bathymetry and heterogeneous soil make this procedure a real challenge. The numerical simulations employ the SITUA-Prosim computational tool, which is able to incorporate the correct definition of the bottom from bathymetric curves. The two crucial points in the performed analyses are: (a) first, to verify if it is possible to move the barge using its own mooring lines in such environmental condition and (b) second, to analyze the pipeline behavior in such scenario.
A Probabilistic Approach to Design Ice Loads for an Arctic Jack-Up Drilling Platform
Authors: Cammaert A. B. , Trumars Jenny , Eide Lars Ingolf
Published: July 2009

The main focus of the paper is to describe a framework for formulating design ice loads for an Arctic drilling platform using probabilistic methods. Particular attention has been paid to the issues of data and model uncertainty and possible effects due to climate change. We apply the methodology to a concept developed by StatoilHydro as a potential configuration for relatively shallow water depths. To minimize and resist ice loads, the concept utilizes a strong central leg and a combined template and platform docking foundation piled to the sea floor. The governing ice loads are due to the action of first-year ice ridges. The ice loads obtained by the probabilistic approach are compared with deterministic model results. A modification of the model is tested for various assumptions related to global warming and its effects on reduced ice coverage and thickness.
A Sea Trial of Wave Power Plant With Impulse Turbine
Authors: Takao Manabu , Sato Eiji , Nagata Shuichi , Toyota Kazutaka , Setoguchi Toshiaki
Published: July 2009

A sea trial of wave power plant using an impulse turbine with coreless generator has been carried out at Niigata-nishi Port, in order to demonstrate usefulness of the turbine for wave energy conversion. Oscillating water column (OWC) based wave power plant has been installed at the side of a breakwater and has an air chamber with a sectional area of 4 m2 (= 2m × 2m). The impulse turbine used in the sea trial has fixed guide vanes both upstream and downstream, and these geometries are symmetrical with respect to the rotor centerline in order to rotate in a single direction in bi-directional airflow generated by OWC. The turbine is operated at lower rotational speed in comparison with conventional turbines. The rotor has a tip diameter of 458 mm, a hub-to-tip ratio of 0.7, a tip clearance of 1 mm, a chord length of 82.8 mm and a solidity of 2.0. The guide vane with chord length of 107.4 mm is symmetrically installed at the distance of 30.7 mm downstream and upstream of the rotor. The guide vane has a solidity of 2.27, a thickness ratio of 0.0279, a guide vane setting angle of 30° and a camber angle of 60°. The generator is coreless type and can generate electricity at lower rotational speed in comparison with conventional generator. The rated and maximum powers of the generator are 450 W and 880 W respectively. The experimental data obtained in the sea trial of wave power plant with the impulse turbine having coreless generator was compared to these of Wells turbine which is the mainstream of the turbine for wave energy conversion. As a result, total efficiency of the plant using the impulse turbine was higher than that of Wells turbine.
Evaluation of Crack Tip Constraint in Pipes Subjected to Combined Loading
Authors: Cravero Sebastian , Bravo Richard E. , Ernst Hugo A.
Published: July 2009

Single edge cracked under tension (SENT) specimens appear as an alternative to conventional fracture specimens to characterize fracture toughness of circumferentially cracked pipes. The similarities of stress and strains fields between SENT specimens and cracked pipes are now well known. However, these similarities are not so well established for the case of circumferentially cracked pipes under combined loading conditions (i.e. internal pressure plus tension, internal pressure plus bending, etc.). This work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed crack configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads.
Design, Manufacturing, Testing, and Deployment of a Cross Haul Bucket for the Independence Hub
Authors: Alexander Chris , Mekha Basim , Hogan Mike , Rager Brent , Kumar Alok
Published: July 2009

This paper provides details on the design, manufacturing, analysis, testing, and deployment of cross-haul buckets used for the pick up, cross haul, and hang off installation of the Independence Hub Steel Catenary Risers in MC 920 in 8000 feet of water depth. The objective in testing was to measure the load capacity of the cross-haul buckets and verify that they were fit for service. The buckets were tested at Stress Engineering Services, Inc. who designed the set up. The test subjects included 20-inch, 10-inch / 8-inch, cross-haul buckets. Strain gages were applied to the lugs of the samples to measure strain during loading. Loads corresponding to the flooded weight of the SCR with dynamic load factors were applied to the samples 15-degrees from vertical (8-inch bucket) and 22-degrees from vertical (20-inch bucket). A 625 mT (1,378 kips) load was applied to the three 10-inch / 8-inch cross-haul buckets and no significant through-wall yielding of the bucket was observed. For the 20-inch cross-haul bucket, a load of 1064 mT (2,345 kips) was applied and no significant through-wall yielding of the bucket was observed, indicating the buckets were adequately design for their intended service.
Development of a Carbon-Fiber Composite Repair System for Offshore Risers
Authors: Alexander Chris , Cercone Larry , Lockwood James
Published: July 2009

Composite systems are a generally-accepted method for repairing corroded and mechanically-damaged onshore pipelines. The pipeline industry has arrived at this point after more than 15 years of research and investigation. Because the primary method of loading for onshore pipelines is in the circumferential direction due to internal pressure, most composite systems have been designed and developed to provide hoop strength reinforcement. On the other hand, offshore pipes (especially risers), unlike onshore pipelines, can experience significant tension and bending loads. As a result, there is a need to evaluate the current state of the art in terms of assessing the use of composite materials in repairing offshore pipelines and risers. The significance of the body of work presented herein is that this study is the first comprehensive evaluation of a composite repair system designed for the repair of offshore risers using a strain-based design method coupled with full-scale prototype testing. This paper presents findings conducted as part of a joint industry effort involving the Minerals Management Service, the Offshore Technology Research Center at Texas A&M University, Stress Engineering Services, Inc., and several composite repair manufacturers to assess the state of the art using finite element methods and full-scale testing methods. Representative loads for offshore risers were used in the test program that integrated internal pressure, tension, and bending loads. This program is the first of its kind and likely to contribute significantly to the future of offshore riser repairs. The end result of this study was the development of a carbon-fiber repair system that can be easily deployed to provide significant reinforcement for repairing risers. It is anticipated that the findings of this program will foster future investigations involving operators by integrating their insights regarding the need for composite repair based on emerging technology.
Computation of Second-Order Wave Forces With a Panel-Free Method
Authors: Peng Hongxuan , Qiu Wei
Published: July 2009

Wave drift forces on floating structures have been computed based on the near-field formulation and a panel-free method. The singular-free boundary integral equation is developed by removing the singularity in the free-surface Green function. The desingularized integral equation is then discretized by Gaussian quadrature over the exact geometry. The Gaussian points coincide with the collocation points. NURBS surfaces are employed to represent the exact body surface. No panelization of the body surface is required. Accuracy of the solution can be enhanced by changing the number of Gaussian points. For illustration, the computational method was applied to a floating hemisphere and a floating box in waves.