bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of Long Axial Corrosion Defects
Authors: Vigsnes Maria , Eldevik Simen , Etterdal Birger , Verley Richard , Krogh Michael
Published: January 2011

Severe Microbiologically Induced Corrosion (MIC) has been discovered in several offshore pipelines, and in particular in water injection pipelines. The corrosion is characterised by long axial channels around the 6 o’clock position. The channelling corrosion generally shows an irregular form which influences the quality of the ultrasonic inspection results; both due to the irregular form itself, and because it affects the ability to clean the pipeline prior to the inspection. The common practice is to produce a feature list reporting the deepest point of a metal loss defect and associate this with a long defect length, typical equal to the pipe joint length for channelling corrosion. Calculating the pressure capacity based on the reported defect depth and length will give a too conservative result for each defect. At the same time; a pipeline with severe channelling corrosion will have many pipe sections subject to an invariant loading condition, and potential structural failure may occur in connection with the lowest structural resistance among the pipe sections. This system effect is a statistical effect that will result in a lower pressure capacity. A procedure to establish the remaining wall thickness profile, a river bottom profile (RBP), based on detailed wall thickness and stand off data from inspections has been developed. A total probability of failure (PoF) for the pipeline given a design pressure is estimated. In case this total PoF exceeds the allowable PoF level, a procedure to establish a pressure adjustment factor, γs, has been developed. This paper outlines the procedure to establish RBPs along the pipeline based on detailed inspection results together with the methodology to calculate the total PoF, including system effects, and the pressure adjustment factor, thus coming up with a pressure capacity at the time of the inspection. The paper also reflects on how consecutive inspections can be used to estimate the yearly corrosion rate between the inspections.
The Effect of Controlling Fins on the Motion of Resonance-Free SWATH (RFS) Platform
Authors: Yoshida Motoki , Kihara Hajime , Iwashita Hidetsugu , Itakura Hiroshi , Bao Weiguang , Kinoshita Takeshi
Published: January 2011

The speed reduction, additional resistance or slamming, which are caused by the large amplitude of ship motions, should be restricted completely for oceangoing large fast ship, because of the strict time-punctuality and high value of the cargo. In the present work, comparison of seaworthiness, such as the motion responses in head seas, is made among four types of ship hulls, i.e. Mono-hull, Ordinary SWATH, Trimaran and Resonance-Free SWATH (RFS). The last one can be regarded as a special type of catamaran. As a result of the extremely small water plane, the restoring moments are negative for RFS hull, which leads to free of resonance in the motion responses. Experiments in towing tank and theoretical calculations are carried out to examine the motion responses in waves. Calculations are generally based on potential theory modified by adding the viscous effects and including fin lifts. The results of the motion responses of RFS are compared with those of mono-hull ship, ordinary SWATH ship as well as trimaran ship. Where the motion of RFS is controlled using movable small underwater fins. The motion of ordinary SWATH is examined with and without fin control. It can be seen that the heave motion responses of RFS are very small in comparison with those of other ship hulls. Also, the pitch motion responses of RFS are much smaller than those of mono-hull or trimaran or ordinary SWATH without fin control, and are smaller than those of ordinary SWATH with fin control. Fin control actions, i.e. proportional and derivative control, are applied in the experiments and calculations. It is considered that the derivative control action is more effective on the motion responses of RFS than the proportional one as predicted. The larger the derivative gain value is, the smaller the motion response of RFS is.
Predicting Wind Loads for FPSO Tandem Offloading Using CFD
Authors: Koop Arjen , Klaij Christiaan , Vaz Guilherme
Published: January 2011

To assess the applicability and accuracy of CFD calculations on typical offshore configurations the wind loads for FPSO tandem offloading is investigated. Within the OO1 JIP windtunnel experiments have been carried out for FPSO’s with different deck configurations behind which a shuttle tanker was positioned. For the CFD calculations presented in this paper one specific set-up is chosen, i.e. a fully-loaded, barge-shaped FPSO with 5 square blocks on the deck and a ballast loaded shuttle tanker at distance 450m. The heading with respect to the main flow direction is 30 degrees for the FPSO and 0 degrees for the shuttle tanker, respectively. For the CFD calculations we choose to ‘model the model’, i.e. the same dimensions for the vessels and tunnel walls are chosen as in the wind-tunnel experiments as well as the same velocity, i.e. 25 m/s, which yields a Reynolds number equal to 2 million. Steady-state solutions are calculated for the FPSO alone at 30 degrees, the shuttle tanker alone at 0 degrees and the shuttle tanker at 0 degrees shielded by the FPSO at 30 degrees with a full-scale distance of 450m. CFX and the MARIN in-house code ReFRESCO are used to investigate the applicability of these tools. Furthermore, the use and accuracy of calculations with different mesh types are investigated by using hexahedral h-refined unstructured grids versus block-structured hexahedral grids, which are constructed with the grid generation packages Hexpress and ICEM-CFD, respectively. The comparison between experiments and computations shows that CFD can provide reasonable answers for the wind coefficients on single vessels. For wind shielding, considerations on the improvement of the overall accuracy of CFD calculations for this type of applications are also presented, as it is found to be difficult to obtain the same results as in the wind-tunnel.
Breaking Wave Impacts on Platform Columns: Stochastic Analysis and DNV Recommended Practice
Authors: Clauss Gu¨nther F. , Haver Sverre K. , Strach Mareike
Published: January 2011

To predict the characteristic impact pressure due to breaking waves on platform columns corresponding to an annual exceedence probability of 10−4 model test data with the Sleipner A gravity based structure (GBS) are subjected to a stochastic analysis. The analysis is based on the environmental contour line approach. In addition, the procedure recommended by Det Norske Veritas (DNV) for calculating shock pressures due to breaking waves is used for comparison. Time histories of pressure and wave elevation for the most severe measured impacts show that the measured pressures are induced by breaking waves. However, a difference between the resulting characteristic impact pressures based on the two approaches can be observed: The stochastic analysis results in much higher pressures than the approach recommended by DNV. These findings are supported by the analysis of data that were collected during model tests with the Gjo̸a semi-submersible and the Snorre A tension leg platform (TLP), where the difference between the results was rather large as well. For the semi-submersible and the TLP, one reason for the difference is bias in the fitment of the stochastic model. Furthermore, dynamic amplification effects in the force sensors have to be considered. However, this bias is less significant for the GBS and dynamic amplification effects are not present since different force sensors were used. For all three model tests, an important source for the different impact pressures is the size of the force sensor area, which varies between 2.25m2 and 10.89m2. Large areas may smoothen the pressure whereas small areas are overrating the impact. Further model testing is required to clarify this effect. If the difference is still present, the recommendation of DNV has to be altered to ensure a reliable prediction of the characteristic impact loads.
On the Interaction of Waves With an Array of Open Chambered Structures: Application to Wave Energy Converters
Authors: Venugopal V. , Bryden I. G. , Wallace A. R.
Published: January 2011

The results of a study carried out to determine the modification of wave climate around an array of open chambered structures, which could represent an array of wave power devices are presented in this paper. The wave-structure interaction is studied using the Boussinesq wave model within the MIKE 21 suite software. The spacing between two adjacent structures within the array is varied from 1S to 5S, where S is equal to 20 m. The effect of varying the spacing between individual structures and the resulting wave reflection and transmission around the array is illustrated using simulated random waves. The results show that the degree of reflection and transmission mainly depends on the spacing between individual structures and the peak wave periods. The maximum increase in significant wave height due to wave reflection in front of the array reached about 39% and the maximum reduction in significant wave height downstream the array is found to be about 41%. The results presented in this paper should be of interest to the wave energy industry.
On Determination of VIV Coefficients Under Shear Flow Condition
Authors: Yin Decao , Larsen Carl M.
Published: January 2011

Long marine risers exposed to ocean currents will experience vortex induced vibrations (VIV), which may cause severe fatigue damage. VIV is, however, generally less understood than other load effects. The offshore oil industry has therefore supported an intensive research activity on VIV during the last two decades. High mode VIV model tests with long flexible riser models were initiated by the Norwegian Deepwater Programme (NDP). A 38 m horizontally towed instrumented riser was tested in uniform and linearly sheared current profiles with varying towing speed. A second series of experiments has been conducted with a motion-controlled rigid cylinder in order to find the hydrodynamic coefficients for realistic cross-section trajectories. The pipe was forced to follow periodic patterns found from the NDP tests with flexible beam. The Reynolds’ number and the non-dimensional frequency, as well the amplitude ratio was kept identical for both types of tests, ensuring that the flow conditions for these two experiments remain the same. The hydrodynamic coefficients calculated from natural trajectories show a general agreement with pure harmonic forced motion tests. A slight change of excitation regions was, however, found for cross-flow response. Another observation is that in-line excitation force coefficients have much higher values than found from pure in-line test.
Long-Term Prediction of Speed Reduction Due to Waves and Fuel Consumption of a Ship at Actual Seas
Authors: Feng Pei Yuan , Ma Ning , Gu Xie Chong
Published: January 2011

The improvement of ship motion and propulsive performance becomes vital in various ocean engineering applications. As the notion of energy saving and environmental protection gradually finds its way deep into people’s heart, the issue of energy efficient design and operation of the vessels has attracted more and more attentions. How to make the vessels maintain service speed while consuming less fuel has quickly become the main concern of the naval architects. In this paper, we present a new procedure to predict speed reduction and fuel consumption of a ship at actual seas. The prediction takes into account the added resistance due to waves since it is recognized to be the predominant component, while wind resistance, fouling effect and other resistance components are relatively small and temporarily ignored. The calculation of the added resistance is based on a three-dimensional frequency-domain panel method for regular waves and spectral approach is applied to obtain the mean value. Then speed prediction is performed based on a simplified model assuming the balanced working point among the ship, propeller and the engine under the assumption of linear relationship between the engine torque and its rotation. Fuel consumption prediction is carried out through calculating the engine power, the effective fuel consumption rate and the time for sailing. Long-term prediction is made through combining the short-term result with the long-term ocean wave statistics from the Database of Winds and Waves which is newly developed in Shanghai Jiao Tong University (SJTU). A long-term probability model which takes into account the ship’s actual navigation conditions is applied, and the expected ship speed and fuel consumption along her actual sea route are predicted accordingly. For the purposed of practical use, a VLCC ship type is adopted for the prediction as an example. Finally, it has been concluded that the propulsive performance, i.e. speed and fuel consumption, of the vessel at actual seas can be improved through design considerations such as hull form optimization, engine selection and weather routing.
A Self-Propelled Deep-Seabed Miner and Lessons From Shallow Water Tests
Authors: Hong Sup , Kimg Hyung-Woo , Choi Jong-su , Yeu Tae-Kyeong , Park Soung-Jae , Lee Chang-Ho , Yoon Suk-Min
Published: January 2011

A self-propelled miner for deep-seabed manganese nodules was developed for the purpose of evaluations of mining performance and viability for scale-up. The test miner crawls on the seafloor by two tracks and separates the nodules from seafloor by hybrid pick-up device. The weight and size are 10tons in air (5tons in water) and 5m(L)×4m(W)×3m(H), respectively. It is operated electro-hydraulically in real-time via umbilical cable. Software’s for real-time remote control, monitoring and database systems were developed as well. Shallow water tests of the test miner were performed in 100m water depth of an inshore condition site. Glass beads (d = 19mm, m = 10g/ea) were made for artificial nodules instead of real nodules. Non DP barge (W = 19m, L = 51m) was used as surface unit. The sea tests showed that the fundamental performance of the test miner is confirmed and at the same time functional modification and improvement in sensing and measurement system are addressed. This paper describes about the development methods of the test miner and lessons from the sea tests.
A Numerical Analysis of the Internal Flow Effect on the Riser’s Mechanical Behavior
Authors: Yamamoto Marcio , Murai Motohiko
Published: January 2011

Pipes are widely deployed in the offshore environment especially in the petroleum industry where rigid and flexible pipes are used for the well drilling and hydrocarbon production. Whereas during drilling, a mixture of drilling mud, rock cuttings and sometimes gas flows through the drilling riser; during production mono or multiphase (comprising oil, water and gas) flow takes place within the production system. However up till now, most of the studies on offshore pipelines and risers have been focused on the pipe structure and its interaction with hydrodynamic forces and offshore platforms. In particular for numerical computation studies and reduced scale model experiments, the pipe is usually modeled as a tensioned beam and sometimes only the internal pressure is taken into account with other effects due to its internal flow being neglected. This paper presents a study on the influence of the internal flow on the pipe’s dynamics. The mechanical behavior of the pipe is modeled using the Consistent Mass and the Finite Element Method (FEM); the effect of an inviscid internal flow is also included. Numerical simulations in time domain have been carried out. Discussion about the experimental results and numerical simulation is also featured.
Response-Based Design Methods for Motion of Turret Moored FPSO
Authors: Rho Junbumn , Lee Jae-Ohk , Sim Woo-Seung , Shin Hyun-Soo , Lee Choong-Dong
Published: January 2011

In this paper, response-based methods are applied to determine response maxima for a floating structure under design environment. Two approaches are adopted to evaluate maximum heave, roll and pitch motions of turret moored FPSO: the conventional long-term simulation approach and the IFORM (Inverse First-Order Reliability Method) approach. First the distributions of environmental variables which are given in metocean data in a form of scatter diagram are described by random variables of relevant probability distribution functions. The simultaneous occurrence of wave, wind and current is taken into account using the joint probability models, and a number of sea-states are generated for the long-term simulations. Heading analysis is performed for a turret moored FPSO in order to obtain relative direction of wave. Short-term analysis is carried out for the numerous generated sea-states with the relative incidences and then long-term analysis follows to predict the maximum motion with the Weibull fitting by method of moments. The sea-state which most influences the maximum responses is chosen according to the probability contribution. In the IFORM approach, the response surface is constructed in the form of polynomials of wave height, direction and period. And the IFORM analysis is carried out using the distribution of environment variables and the response surface functions, and the maximum resultant heave, roll and pitch motions are evaluated for the given design return period. The combinations of wave height, period and direction causing response maxima are identified as well. The 100-year values of heave and pitch from the IFORM analysis is determined higher than those from the long-term simulation due to the simplified description of heading distribution whereas similar sea-states are identified by the two approaches. The 100-year roll motion can be determined using IFORM by neglecting the conditional probability of direction and period to height. Similar 100-year RP roll values are estimated from both the long-term simulation and the IFORM analysis, however, the sea-states of maxima occurrence are different because wave height governs the probability exceedence much more than period and direction in the IFORM. Finally the values from response-based methods get consistently lower than those from traditional extreme analysis which calculates responses for the 100-year extreme environment.
Advanced Titanium Oxide Steel With Excellent HAZ Toughness for Offshore Structures
Authors: Fukunaga Kazuhiro , Chijiiwa Rikio , Watanabe Yoshiyuki , Kojima Akihiko , Nagai Yoshihide , Mamada Nobuhiko , Adachi Toshihiko , Date Akihiro , Taniguchi Syunsuke , Uemori Ryuji , Nishimura Seiji
Published: January 2011

The feature of titanium oxide steel (Ti-O steel) is that heat affected zone (HAZ) toughness is improved due to the refinement of HAZ microstructure through the formation of intragranular ferrite (IGF). This desirable microstructure, IGF, forms radially from titanium oxide particles. Recently, it has been clarified that manganese in Ti-O steel is an indispensable element for the formation of IGF. Therefore, manganese effects on Ti-O steel have been basically studied in this work, and then a new effect has been found. In Ti-O steel, manganese has the effect of suppressing the formation of ferrite side plates (FSP), which are undesirable due to their coarseness. Consequently, HAZ microstructure of Ti-O steel with high manganese content is so refined that HAZ toughness is remarkably improved. Based on the manganese effects, steel plates with excellent HAZ toughness for offshore structures have been developed and commercially mass-produced. The welded joints exhibit excellent toughness.
New Attempts in the MR-X1 Sea-Trials: The Working AUV Tries to Survey of the Sea Floor and to Take Mud Samples
Authors: Yoshida Hiroshi , Hyakudome Tadahiro , Ishibashi Shojiro , Takao Sawa , Nakamura Masahiko
Published: January 2011

Autonomous underwater vehicles (AUVs) allow us to survey and explore globally and freely in vast deep sea. We aim to develop long cruising range AUVs (LCAUVs) for researches of the global change, ocean-trench earthquake, and biodiversity and for exploring ocean resources. We have developed the first prototype of LCAUV, Urashima since 1998. The vehicle powered by a PEFC system marked the world record of cruising distance of 317 kilometers in 2005. The vehicle, 10 m long and 10 tons in weight, has the specifications: maximum depth ratings; 3500 m, maximum cruising speed; 3.2 knots, and endurance; 60 hours. This large vehicle has large user payload of a few hundreds kilograms. In 2007, research and development of the elemental technologies which will be utilizes for development of the second generation LCAUV started to expand cruising range to 3000 kilometers. For long range cruising, technology improvement of power sources, navigations, communications, and vehicle controlling are mainly important. Since endurance of the LCAUV becomes over 600 hours, during this cruising period the vehicle controller must autonomously deal with problems which may occur in any devices. If the vehicle controller does not recover a fatal problem, the controller appropriately leads status of the vehicle to quit an executing mission and ascend itself. We have improved the vehicle controller and plan sea-trials using the controller in January 2009. On the other hand, The AUV, MR-X1, 2.4 m long and 800 kg in weight, has been developed for scientific research and the test bed of the LCAUVs since 2000. This working AUV is also needed for installing or recovering observation equipment, tracking and sampling benthos or planktons, and doing simple repetitive works. The first sea-trial of MR-X1 was carried out in 2003. After that, the MR-X1 system is only used as a test bed of the developed devices in the LCAUV project. In this year, we have developed new items, a device installer on the sea-floor and mud core sampler for the MR-X1. In the technical report, a redundant controlling system for the LCAUV installed on the MR-X1 is described. And new items and their test results will be reported.
Using ECA in Structural Integrity of Submarine Pipelines for Optimalization of Intervention Work
Authors: Igland Ragnar T. , Lamvik Trond
Published: January 2011

The paper deals with the design methodology to define the design loads and determine the maximum allowable size of girth weld defects. The motivation for this work is reduced intervention costs obtained by opening all free spans as these are governing for rock infill volumes. 20–30% reduction of the intervention work is obtained. Structural integrity of the pipeline related to the interference with fishing gear is an important design scenario. Trawling in free span, pull-over loads with clump weight as an ALS condition is the main issue. REINERTSEN observed during detail design a lack of acceptance criteria for ALS conditions in the DNV OS-F101 design code, Ref. [1] for interference between trawl gear and subsea pipelines with low D/t ratio. Curvature in the trawl pull-over point as a function of time is found approximately constant while trawl load is increasing. The membrane forces carry most of the trawl load a few seconds after the trawl impact while bending moment decreases. This is in accordance to the philosophy that the strain and the curvature will be nearly constant for increased loading. The global load bearing mechanism is membrane and less bending. This means that we have control on the strain and that the pipeline system maintains its stiffness against loading for this high axial capacity of the flowline. These observations leads to a deformation controlled trawl load approach where an ECA of the flowline can be used to document structural integrity. Engineering Criticality Assessment (ECA) analysis is applied to evaluate the integrity of the flowlines with respect to risk for unstable fracture in girth welds due to impact from trawl equipment. The fatigue load effects from installation, temporary and operational phases are included in the ECA analysis. Geometric effects and external/internal pressure are included using the tailormade softwares LINKpipe, Ref. [7] and Crackwise4, Ref. [8]. The residual capacity of the flowlines is calculated with emphasis on fatigue during operation after the trawl pull-over. The fatigue life should be within the inspection interval, reflecting the Integrity Management Scheme.
Numerical Investigation of a Ship Collision With Waterway Embankments
Authors: Qiu Gang , Grabe Ju¨rgen
Published: January 2011

During the last century there has been an increase in frequency of ships colliding with waterway embankments of inland waterways. The increasing occurrence of shipping accidents threatens the safety of freights and the serviceability of existing structures, such as tunnel and bridge abutments which are located near embankments. It is necessary to develop a method enabling prediction of the collision force and the stopping distance of a collision ship. In the related project “Hochdonn” of BAW (Federal Waterways Engineering and Research Institute, Germany) collision experiments were performed to analyze the impact mechanisms in grounding problems. A 3D FE model using a Coupled Eulerian Lagrangian approach is used to recalculate the collision experiment of BAW with the test ship “Gerda”. The stopping distance and the reaction force that are indicated by the numerical simulation match the field test results very closely. In addition two parametric studies are undertaken to quantify the influences on the collision process from the initial velocity as well as the bow type of the ship.
Breaking Wave Impacts on Offshore Wind Turbine Foundations: Focused Wave Groups and CFD
Authors: Bredmose Henrik , Jacobsen Niels G.
Published: January 2011

Extreme wave loads from breaking waves on a monopile foundation are computed within a 3D CFD model. The wave impacts are obtained by application of focused wave groups. For a fixed position of the monopile, the focus location of the wave group is varied to produce impacts with front shapes that varies from early stages of breaking to broken waves. The CFD results for in-line force are compared to load estimates obtained from the Morison equation. The peak loads determined with this simple method are smaller than those of the CFD solution. The computational results appear to suggest that for the impacts of spilling breakers the peak force gets smaller the more developed the breaking is. This is in qualitative agreement with a finding from shallow water impacts on vertical walls: the strongest wave loads are associated with breakers that hit the structure with slightly overturning front. Extensions of the study are discussed.
Analysis of Uncertainties in the Estimation of Fatigue Damage in Maritime Structures by the Bootstrap Technique
Authors: Vasconcelos Antonio , Prates de Lima Edison Castro , Sagrilo Lui´s Volnei Sudati
Published: January 2011

This work describes the application of the Bootstrap technique to assess relevant information about the structural damage due to the action of a random loading time domain simulation. The Bootstrap methodology allows the estimation of the standard deviation confident interval calculated over a single time domain analysis. Two numerical applications are presented to exemplify the using of the confident intervals to obtain information on the cumulative damage of a structure subject to these random loadings.
Hull Optimization of the Unmanned AGaPaS Rescue Vessel
Authors: Clauss Gu¨nther F. , Kauffeldt Andre´ , Otten Nils , Stuppe Sven
Published: January 2011

Crew safety is a key parameter for any seagoing mission. Although today’s standards are high, occasionally people go overboard while working on deck. In this case the probability of survival remains low. The joint research project “AGaPaS” [1] aims to significantly increase the chances of survival for a drifting person. Its main objective is to develop a self activating, partially autonomously operating rescue system, able to search, find and rescue people gone overboard. A crucial part of the system is a remotely operated vessel, which is released by free fall from a mother ship. This paper focuses on the hull optimization of this rescue vessel, considering various aspects. The rescue operability has first priority and leads to numerous system specifications such as main dimensions. In addition, adequate seakeeping behaviour is a prerequisite for the successful recovery of a person in distress. This includes small relative motions between the vessel and the drifting person. Moreover, the vessel’s free fall characteristics are to be analyzed. Here, particular interest has been laid on the reduction of the peak acceleration as well as on transferring the vertical velocity into a horizontal motion, in order to minimize the risk of a collision with the mother ship. Various hull geometries have been investigated by means of numerical methods as well as model tests leading to the final hull design of the unmanned AGaPaS rescue vessel.
Bending Capacity of Pipe Bends in Deepwater Conditions
Authors: Liu Shulong , Walker Alastair , Cooper Philip
Published: January 2011

Offshore pipeline systems commonly incorporate induction-heating formed bends along flowlines and in pipeline end termination assemblies and spools. In deepwater locations, the pipeline and bends are subjected to various combinations of external pressure, internal pressure, bending moment and temperature changes, during installation, and operation. Although there is a history of research into the limiting loads and failure modes of such bends and pipelines systems there is, as yet, no comprehensive guidance to enable the calculation of the maximum capacity under combined bending and external pressure loading. Conservative guidance is presented in DNV OS-F101 (2007) [1] that proposes increasing the pipe wall thickness to reduce the effect of external pressure collapse effects thus enabling bending formulations relevant to straight pipe to be used. This proposed approach leads to unfeasibly large wall thickness requirements in very deepwater applications. There is therefore a requirement for a method to design deepwater bends for installation and operation conditions with levels of safety comparable with those used in the design of straight sections of pipelines that does not depend on the requirement to increase the wall thickness to the extent proposed in the current DNV guidance. In this study, a nonlinear FE method using ABAQUS is proposed to evaluate the ultimate capacities of induction-heating formed bends. The method takes into account the combined effects of non-linear material properties, initial ovality, wall thinning/thickening, external or internal pressure, internal CRA cladding and temperature change on the ultimate moment capacity of the bend. The numerical model is validated by comparison with available published results. The method developed here is based on the limit state design formulations in the current DNV OS-F101 guidance.
An Analytical Model for the Unbonded Flexible Pipe Stress Analysis With Consideration of Nonlinear Material Properties for Metal Layers
Authors: Liu Jian , Tan Zhimin , Sheldrake Terry
Published: January 2011

This paper presents an improved analytical model for the unbonded flexible pipe stress analysis with consideration of nonlinear material properties for metal layers. Analytical methods have often been used to analyse the stress and strain of flexible pipe systems because of their low cost and efficiency compared with detailed finite element modeling. Most of these kinds of models only consider the deformation of pipes within the elastic region. Such linear models can not be used directly to assess pipe failure modes such as the pipe burst strength, where the nonlinearity of the metallic material plays an important role in governing the pipe deformation and pipe structural capacity. The improved analytical model presented in this paper has fully considered the nonlinearity of metal layers such as the pressure armour and tensile armour layers because of their importance in resisting internal pressure and tension loads. Non-associative elasto-plastic stress strain curves obtained from experiments are used to simulate the metal layers. Von Mises stress is adopted in the model as the yield criterion of the metal layers. Radial return method (Simo and Taylor 1985 [1], Simo and Hughes 1998 [2]) is used to solve the plastic stress and strain of metal layers beyond the yield point. Due to its high nonlinearity from both system equations and material properties, Newton-Raphson method is adopted in the model as the solving method. The proposed study here considers tension, torque and pressure loads only for a straight pipe. The model predictions have been compared against measurements from Wellstream burst tests and failure tension tests performed over the full scale pipe samples. The prediction and experiment results agree.
Influence of Nonlinear Mechanical Contact on Hang-Off Location in Flexible Risers’ Structural Response
Authors: Rocha Germayne , Parrilha Rafael , Martins Oliveira Albert
Published: January 2011

The safe design of flexible pipe on top near its support, in even more challenging deepwater loading conditions, requires more advanced studies to contribute to a better understanding of the influence of nonlinearities on the riser structural response in time-domain numerical computational analysis. The flexible structural non-linear dynamic analysis took into account risers terminated on spider deck passing through I-tube structure which applies lateral movement restriction represented by annulus area of contact elements. Axial movement is free although limited by a minimum slack in the riser guide until the bend stiffener conical interface. This work presents the main outputs of a sensitivity study of the flexible riser dynamic analyses installed in semi-submersibles. Amongst the main benefits of the project are comparisons between a simplified pontoon configuration model x sophisticated spider deck configuration model. The study presents the relevant differences and the level of conservatism inherent to each analyzed configuration models. Critical analysis of the flexible riser response was carried out given critical loading cases and compared among distinct riser specifications in terms of moment and force transmissions from the working point of the bend stiffener to the I-tube support at the bell mouth elevation providing us more realistic interpretation relevant to design reliability of the platform I-tube structure. In addition, the present work aims to study the influence of nonlinearities in the bending moment cumulative distribution and in the damage calculation derived from the dynamic analysis riser response in the top region under extreme far loading conditions.
Computational Models for Prediction of Performance and Design of Tidal Turbines
Authors: Kinnas Spyros A. , Xu Wei , Yu Yi-Hsiang
Published: January 2011

In this paper, the performance of a horizontal axis, 3-blade tidal turbine is predicted by a vortex lattice method, in which the fully unsteady wake alignment is utilized to model the trailing wake geometry. A blade design procedure, which combines a lifting line approach with the vortex lattice analysis method and a nonlinear optimization scheme, is proposed.
A Comparative Analysis of Ultra Deep Water Catenary Rigid Risers
Authors: Morooka Celso K. , Suzuki Mauricio J. H. , Pereira Paulo S. D.
Published: January 2011

The ever increase of global demand for petroleum and natural gas brings needs to discover new petroleum fields. Particularly in the Brazilian coast, these discoveries are located on more and more remote areas combined with harsh and aggressive petroleum fluid production, such as the case of recently announced pre-salt petroleum fields. Development of offshore systems for field production in this scenario demands sophisticated and innovative technological solutions. It brings the necessity for developments of frontier technologies to make viable design of oil and gas production systems to be applied for ultra deep water depth applications. Production riser is a very critical component of most offshore petroleum production systems. Riser acts as a physical connection between subsea wells and floating production facility at the sea surface. It conducts the oil and gas production, and sometimes, fluid or gas for injection into the petroleum reservoir. Wellhead control commands are also guided between the floating platform and the subsea system throughout the riser system. In the literature, many different riser systems have been proposed and extensively discussed for ultra deep water applications. Among others configurations, Steel Catenary Riser (SCR) appears as a technically feasible and economically viable solution. This system is comprised with a free hanging steel pipe, suspended from the platform directed to the wellhead in a catenary shape. In ultra deep water, the riser weight itself commonly is the limitation for application of this type of riser system. Once it requires a much more expensive floating production platform with larger capacity. Furthermore, it also can cause high concentrated stresses in some regions along the riser structure. Catenary shaped risers with lighter material such as Aluminum seem to be a very attractive alternative due to the great riser weight reduction observed. The present paper describes and proposes procedures for the design and operation of petroleum production riser system for ultra deep water application to produce high flow rate of oil and gas in a typical pre-salt petroleum field offshore Brazil condition. Results and discussions are shown through comparisons for catenary riser systems composed by steel pipe and other kind of lighter material. Case studies are conducted for water depth up to 3000 meters by parametric analysis. Current and waves effects along with floating platform motions and riser geometries are analyzed in order to identify critical conditions and to depict feasible solutions.
Salinity Response to the Runoff From Yangtze River Basin at Qingcaosha Reservoir Area in Yangtze Estuary
Authors: Tong Chaofeng , Zheng Jinhai , Zhang Cheng , Guilbaud Claude
Published: January 2011

Qingcaosha Reservoir locates in the Yangtze Estuary of China is an estuary reservoir. As the third water source region of Shanghai city, about 717,000 m3/d raw water will be supplied from the Reservoir when the project is finished. In order to avoid salt water from saltwater intrusion, it is necessary to reveal the rule of salinity variation in the Qingcaosha Reservoir area. Saltwater intrusion in the Yangtze Estuary is mainly impacted by the fresh water discharge from the Yangtze River and the open sea tides. The salinity response of Qingcaosha Reservoir area to the runoff will be discussed. In the paper, the hydrodynamic and saltwater intrusion model of Yangtze Estuary is developed and calibrated with the TELEMAC model. The model domain covers the whole Yangtze Estuary and the Hangzhou Bay. Hydrological data of 9 tidal stations and 5 current measuring points during spring tide, middle tide and neap tide in March, 2002, are used to calibrate the salinity data. Comparisons of the calculated results and measurements show that the hydrodynamic model and the salinity model can reflect precisely the law of currents and the salt water intrusion in the Yangtze Estuary, and they can be used to forecast the salinity in Qingcaosha Reservoir region. According to the different characteristic discharges corresponding to the different cumulative frequencies, the salinity distributions in Yangtze Estuary are calculated under the conditions of different flow into the sea. The simulation results show that the salinity values will decrease with the increasing of discharge. When the upstream discharge is below 16,700 m3/s, the average value in dry season, the salinity response to the runoff is very sensitive. The salinity amplitude at the downstream gate area is inversely proportional to the upstream discharge, whereas, the parameter at upstream gate area is proportional to the upstream discharge if it isn’t up to the average value in dry seasons. The salinity at the downstream area of reservoir is obviously higher than that at the head region.
Concept Design of Mining System of Seafloor Hydrothermal Deposit
Authors: Takagawa Shinichi
Published: January 2011

Japan Deep Sea Technology Association had carried out concept design of the mining system for seafloor hydro-thermal deposit from 2008 through 2009. Through this concept design, the economic evaluation of the system with parameter of annual production of the ore was discussed, and it was clarified that more than 500 thousand tons annually would enable us to get positive balance. The environmental effect by mining was also discussed and was concluded that the active hydrothermal vents are not the targets of mining, instead, the dead vents are the targets. Then, the technological feasibility of each subsystem was discussed which constitutes the mining system, from the digger to the surface transporter. Finally, it was concluded that the mining system for hydrothermal deposits is feasible using the state-of-the-art technology even in rough sea around Japan.
A Preliminary Study on the Interaction Between Slug Flow and Vortex Induced Vibration in Fatigue Life of Submarines Pipelines
Authors: Blanco Armando , Casanova Euro
Published: January 2011

Flow induced vibrations is a very important subject that should be carefully considered when facilities to transport hydrocarbons from marine sub-sea to shore line are designed. In particular, interaction between internal pipeline flow and external marine currents on horizontal, inclined or vertical (i.e. risers) pipelines need to be considered to properly estimate their fatigue life. Between these two form of excitations a coupling of resonances may appear, thus producing fatigue life predictions different from those calculated when each excitation is considered separately. In this paper a fluid-structural model for analyzing the dynamical behavior of a riser subjected to simultaneous internal slug flow and an external marine current uniform flow was developed. The fluid model was based on the classical wake oscillator model. A numerical model based on the finite difference method was implemented for the structure. Different tests cases were modeled to analyze the riser dynamics for a typical field case, when marine current velocity is constant. Preliminary results show that, in some cases of practical interest, the dynamical behavior of the riser could be influenced by the slug flow and the predicted fatigue life may be different from those predicted when each flow is considered separately. Additionally, results show that study of different slug flow scenarios may be simplified considering a monophasic flow whose density is equivalent to that of the average slug flow density.
Deepwater Rigid Spools Slugging Flow Fatigue Design
Authors: Zhao Tao , Cooper Philip , Brugmans Joost
Published: January 2011

Tie-in spools form an important part of any deepwater flowline system. Successful designs have the potential to deliver significant savings in fabrication, transportation and installation costs, whilst protecting project schedules. For multiphase flowlines, slug-induced fatigue damage has emerged as a governing design criterion in recent projects. Spans have become the focus of attention for slug-induced fatigue damage. These may occur at tie-in spools used to connect flowlines in deepwater developments. Conventional piping design software tools are commonly used for rigid spools design. Limitations/disadvantages of conventional tools were identified by comparison with detailed simulation of critical aspects of the design using more advanced numerical simulation tools. Rigorous 3D numerical dynamic analysis was used to simulate gravity variation of the slugs and bubbles, and the dynamic impact effect due to the passage of slugs through bends. Resonance effects of spools exposed to slugging flow were inspected and the cause of spools resonance was investigated. The consequential fatigue damage was computed using a time-domain FEA and rainflow counting algorithm. While conducting slugging flow fatigue FEA, bespoke pipe-soil interaction models were developed to simulate cyclic lateral and vertical resistances of the very soft seabed soils typically found in deepwater fields. A contact technique with nonlinear normal and decoupled bi-axial tangential interactions was implemented using FORTRAN subroutines. The analysis procedures developed are outlined, and typical spool designs are presented. The paper seeks to understand the slugging flow effects to the deepwater spools fatigue design, fatigue design, especially while the spools resonance can not be mitigated, and provide the optimised spool configuration in which the slugging effects are minimised, taking due account of the complexities outlined above.
Pilot Model Tests on the ‘Green Water Concept’ for Wave Energy Conversion With Model Scale Power Take Off (PTO) Modelling
Authors: Buchner Bas , van der Schaaf Haite , Hoefakker Koos
Published: January 2011

This paper presents the pilot model tests on the ‘Green Water Concept’ for wave energy conversion. These tests also included the initial modelling of an electric and hydraulic Power Take Off (PTO). The accurate modelling of a PTO is an important aspect in testing of wave energy conversion concepts numerically and in a wave tank: at the moment that energy is converted into electricity in the PTO, the hydrodynamic behaviour of the structure is changing. The present tests confirmed the high motions and large amount of green water of the Green Water Concept as predicted in previous simulations. The application of a real PTO gave important insight in the possibilities and challenges of PTO modelling at model scale. For the present concept a mean Power (at full scale) close to 1MW was generated in a regular wave of H = 3.0m for the maximum possible setting in the chosen test set-up. This setting was limited by the chosen mechanical and electronic motor set-up in this pilot test series, not the actual maximum of the Green Water Concept itself. Considering the test results, it is clear that the potential of the system is significantly larger.