bluuebunny/crossref_metadata_2025 huggingface dataset:
Reeling Analysis Including Strain Concentrations at Girth Welds
Authors: Soreide Tore , Trier Sigurd , Erixon Bo
Published: January 2011

Dimensional variations across a girth weld undergoing reeling leads to strain concentrations close to the weld that have to be taken into consideration in crack growth evaluations. The aim of the present paper is to outline an analysis procedure for simulating the complex load history, and to illustrate the effect of material and wall thickness variations between the two joints on each side of the girth weld. Verification analyses are also made towards full-scale tests simulating the cyclic loading during the reeling process. The computer software ANSYS was applied with contact and plasticity formulation, and the load history through reel, aligner and straightener was modelled. A combination of beam and shell elements was applied for the pipe, ending up in an efficient tool for design analysis. The nonlinear material model included kinematic hardening and was based upon a Ramberg-Osgood type of stress-strain curve. The effect of kinematic hardening through cyclic loading was studied in an effort to define the material properties of the as-installed pipe. The numerical model also came out with contact pressures between the reel and the pipe, being of special interest for thermally coated pipes. Ovalisation of the pipe was available, and goes into the bending moment capacity for expansion control. A full-scale bending test of clad pipe around a girth weld was performed, simulating the load history through the reeling process. Measured strains and forces were compared with numerical results as a verification of the analysis model. A separate ANSYS model was created for the test case, based on the material models in the global model. The location of strain concentrations in the vicinity of the girth weld was given special attention in the comparison between tests and numerical simulation. Material tests for backing steel and clad, respectively, around the circumference of the as-tested pipe illustrate the strain hardening effect as basis for evaluation of the kinematic hardening parameters implemented in the numerical models. Analyses were then used for a parameter study on strain concentrations with yield stress and wall thickness variations across the girth weld. Also, the amplifying effect of local buckling during reeling is evaluated, as basis for defining needed back-tension.
On Penetration of Upright and Tapered Suction Caissons in Sand: An Experimental Study
Authors: Kakasoltani Siamak , Zeinoddini Mostafa , Abdi Mahmoud R. , Mousavi Behnam Seyyed Abbas
Published: January 2011

Over the past two decades, suction caissons have been increasingly utilized as deep water anchors for floating structures, foundations of offshore wind turbines and even for jacket platforms. They penetrate into the sea bed by a combination of their buoyant weight and under base suction. Suction caissons have appeared as an efficient and economic alternative for foundations in the offshore industry. This concept, however, is relatively new, so the knowledge about their behavior has not yet gone far deep as that for other offshore foundation solutions such as driven pile systems. This paper reports some results from an experimental investigation into the installation of upright and tapered suction caissons. The 1g experiments have been carried out on eight small scale suction caissons. The aspect ratios, (the caisson length/its diameter) have been 1, 2, 3 and 4. The diameter has been constant and equal to 80 mm. Four specimens have had upright walls while the other four had a positive wall slope of 10%. The caissons have been installed in a soil tank containing very fine saturated silty sand. The penetration has been achieved under forced driving using a constant penetration rate. The effects of geometrical parameters and the soil density on the overall penetration force have been studied. it has been observed that, with both the upright and tapered caissons, the required force for full penetration increases by an increase in the aspect ratio. The penetration force required for full penetration of tapered models, has been two to three times higher than an equivalent upright caisson. With tapered caissons, the penetration forces have been found to be more sensitive to the soil density as compared to that with upright caissons. The experimental results for upright suction caissons have also been compared with a closed form analytical solution proposed by other researchers.
Study on Collision Forces on Water-Front Facilities Induced by Floating Vessels Washed Onto Apron by Tsunami
Authors: Masuda Koichi , Masuda Mitsuhiro , Ikoma Tomoki
Published: January 2011

The present paper describes the application of the moving particle semi-implicit method to a prediction of collision forces on water-front facilities induced by floating vessels washed onto the apron by tsunami. Effectiveness of the application is verified. Solitary waves are applied to simulated tsunamis in numerical simulation and to the model experiments. A pontoon type floating body is applied to floating structures in numerical simulations using the MPS method. The present calculation results are compared with the experimental results and the applicability of MPS method is discussed. Further, after being washed onto the wharf by tsunami, the characteristics of collision force on water-front facilities induced by the floating bodies are discussed.
An Efficient Monte Carlo Simulation Technique for Derivation of the Probability Distribution of the Extreme Values of Offshore Structural Response
Authors: Abu Husain M. K. , Najafian G.
Published: January 2011

Offshore structures are exposed to random wave loading in the ocean environment and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. To this end, the conventional simulation technique (CTS) is frequently used for predicting the probability distribution of the extreme values of response. However, this technique suffers from excessive sampling variability and hence a large number of simulated response extreme values (hundreds of simulated response records) are required to reduce the sampling variability to acceptable levels. In this paper, a more efficient version of the time simulation technique (ETS) is introduced to derive the probability distribution of response extreme values from a much smaller sample of simulated extreme values.
Derivation of Water Particle Kinematics in the Near Surface Zone by the Effective Water Depth Procedure
Authors: Mohd Zaki N. I. , Najafian G.
Published: January 2011

Linear Random Wave Theory (LRWT) is frequently used to simulate water particle kinematics at different nodes of an offshore structure from a reference surface elevation record. However, it is well known that LRWT leads to water particle kinematics with exaggerated high-frequency components in the vicinity of mean water level (MWL). To avoid this problem, empirical techniques (such as Wheeler & vertical stretching methods) are frequently used to provide a more realistic representation of the wave kinematics in the near surface zone. In this paper, a modified version of LRWT, based on the derivation of an effective water depth, is introduced. The proposed technique leads to predicted kinematics (in the near surface zone) which lie between corresponding values from the Wheeler and the vertical stretching methods. Furthermore, it does not suffer from exaggerated high-frequency components in the near surface zone.
Conceptual Design of OWC Wave Energy Converters Combined With Breakwater Structures
Authors: Sundar Vallam , Moan Torgeir , Hals Jo̸rgen
Published: January 2011

Ocean wave energy is one of several renewable sources of energy found in the ocean. The energy in the oscillatory ocean waves can be used to drive a machinery that converts the energy to other forms. Depending on the type and their location with respect the coast and offshore, a number of devices have been and are being developed to extract the wave energy for conversion into electricity. The most common devices are referred to as the oscillating water column (OWC), hinged contour device, buoyant moored device, hinged flap and overtopping device. Particularly popular are OWCs and moored floating bodies. The idea of integrating breakwater and wave energy converters emerged in the Indian wave energy program. Graw (1996) discussed this idea and pointed out the advantage of shared costs between the breakwater and the wave energy device. Because long waves are usually experience stronger reflection at coasts and breakwaters, they provide good conditions for the operation wave energy devices which work efficiently when the reflection is high. There are examples that OWC devices have been installed in water as shallow as 3 m. This paper reviews the options of integrating OWCs with different kinds of breakwaters like the perforated or non-perforated caisson breakwater, and non-gravity piled and floating types. The purpose of each of the concepts will also be highlighted.
Buckling of Unstiffened Steel Cones Subjected to Axial Compression and External Pressure
Authors: Blachut J. , Ifayefunmi O.
Published: January 2011

The paper considers buckling of unstiffened truncated conical shells under simultaneously acting quasi-static axial compression and an independent external hydrostatic pressure. This is both numerical and experimental study. Domains of combined stability were obtained using the finite element method for a range of geometrical parameters. Cones are clamped at one end and free to move axially at the other end, where all the other degrees of freedom remain constrained. Shells are assumed to be from mild steel and the material is modeled as elastic perfectly plastic. The FE results indicate that the static stability domains remain convex. The failure mechanisms, i.e., asymmetric bifurcation and axisymmetric collapse are discussed together with the spread of plastic strains through the wall thickness. Also, the combined stability domains are examined for regions of purely elastic behavior and for regions where plastic straining exists. The latter is not convex and repercussions of that are discussed. The spread of the latter is computed for a range of the (radius-to-wall-thickness)-ratios. Experimental results are based on laboratory scale models. Here, a single geometry was chosen for validation of numerically predicted static stability domain. Parameters of this geometry were assumed as follows: the ratio of bigger radius, r2, to smaller radius, r1, was taken as (r2/r1) = 2.02; the ratio of radius-to-wall-thickness, (r2/t), was 33.0, and the cone semi-angle was 26.56°, whilst the axial length-to-radius ratio was, (h/r2) = 1.01. Shells were CNC-machined from 252mm diameter solid steel billet. They had heavy integral flanges at both ends and models were not stress relieved prior to testing. Details about the test arrangements are provided in the paper. In particular, the development details and experience of the test rig for independent/combined loading of cones are given. The current contribution complements Ref. [1].
Numerical Modelling of Wave-Induced Pore Pressure Around a Buried Pipeline: WSPI-3D Model
Authors: Shabani Behnam , Jeng Dong-Sheng , Ye Jianhong , Guo Yakun
Published: January 2011

In this paper, a three-dimensional numerical model is developed to analyze the ocean wave-induced seabed response. The pipeline is assumed to be rigid and anchored within a trench. Quasi-static soil consolidation equations are solved with the aid of the proposed Finite Element (FE) model within COMSOL Multiphysics. The influence of wave obliquity on seabed responses, the pore pressure and soil stresses, are studied. A comprehensive tests of FE meshes is performed to determine appropriate meshes for numerical calculations. The present model is verified with the previous analytical solutions without a pipeline and two-dimensional experimental data with a pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. However, the influences of wave obliquity on the wave-induced pore pressure are insignificant.
Fatigue Assessment of Welded Joints Taking Into Account Effects of Residual Stress
Authors: Syahroni Nur , Berge Stig
Published: January 2011

Residual stress may have a significant effect on the fatigue strength of welded joints. As a non-fluctuating stress, it has an effect similar to that of the mean stress. Recently the International Association of Ship Classification Societies (IACS) has issued Common Structural Rules (CSR) for respectively tankers (IACS 2006a) and bulk carriers (IACS 2006b). The effect of mean stress in fatigue design is taken into account in both sets of rules. However, the treatment is quite different, in particular with regard to residual stress and shakedown effects. In the present paper a comparative study of fatigue design procedures of the IACS rules is reported, with emphasis on residual stress effects. Testing was carried out with longitudinal attachment welds in the as-welded condition. The initial residual stress was measured by a sectioning method using strain gages. Hot spot stress was determined experimentally by strain gauges and numerically by finite element analysis using different types of elements. Fatigue testing was carried out and SN-curves were plotted according to the relevant stress as specified by the rules. In order to investigate the shake-down effect of residual stress, testing was performed for several pre-load conditions which could be taken to represent maximum load levels in a load history. The aim of the study is to contribute towards better understanding of the effect of residual stress and shakedown on fatigue strength of welded joints.
A Basic Study on Wind Pressure Characteristics of a Trimaran PCC
Authors: Nihei Yasunori , Li Qiao , Nakashima Takuji , Ikeda Yoshiho
Published: January 2011

In recent years, the marine transport of a car is activated, and the demand for a pure car carrier (PCC) has grown quickly in the world wide. However, there are lots of technical issues of the present PCC, like lack of stability, effect of strong winds on its resistance, difficulty of course keeping in rough seas, difficulty of berthing in strong winds and so on. To overcome these technical issues, one of the authors has proposed a trimaran PCC which has very limited number of transverse bulkheads in the center hull by using two side hulls as fenders. In this study, wind forces and moments acting on a scale model of the trimaran PCC are measured in the towing tank with wind fans of Osaka Prefecture University. Furthermore, in order to find the parameters affecting on wind pressure, height and width of tunnels which are between a center hull and two side hulls are changed. To analyze it qualitatively, the flow field around the body is calculated by CFD. The wind pressure acting on the body is compared with that on a mono-hull PCC. Using these experimental and theoretical results, the wind pressure characteristics of a trimaran PCC are obtained.
Numerical and Model Test Investigation on the Motion Characteristic of FDPSO and the Sheltered Riser Vessel
Authors: Wei Yuefeng , Hu Zhiqiang , Chen Gang , Yang Jianmin
Published: January 2011

FDPSO is a multifunction floating platform, capable of drilling, production, storage and offloading. Sheltered Riser Vessel (SRV) serves as an independent buoyant hull to provide riser tensions, which is situated in the moon pool of FDPSO. Due to the shielding effect of moon pool, the motion of SRV is very small, so as to meet the requirement of drilling. In order to validate the basic FDPSO and SRV concepts, a model test was conducted in the basin of Ocean Engineering in the State Key Lab of Ocean Engineering in Shanghai Jiao Tong University. The storm tests were carried out in wave extremes of West Africa and white noise wave environments. Potential theory was adopted to calculate the motion performance of FDPSO system. Frequency domain analysis of the motion response amplitude operator (RAO) and time domain analysis in the extreme sea condition are both conducted. The comparison between the numerical simulation and model test results shows that the results of RAO and statistical value of response time series in the extreme sea condition are coincident. It is indicate that the method is credible and the concepts of FDPSO and SRV are likely to be feasible in West Africa.
Support Structure Reliability of Offshore Wind Turbines Utilizing an Adaptive Response Surface Method
Authors: Tho¨ns Sebastian , Faber Michael H. , Ru¨cker Werner
Published: January 2011

This paper focuses on a reliability analysis of an offshore wind turbine support structure which is part of an assessment and monitoring framework for wind turbines in operation. The reliability analysis builds upon structural, loading, limit state and uncertainty models comprising design, production and erection data. This model basis facilitates the reliability analysis of the ultimate, the fatigue and the serviceability limit states utilizing stochastic finite elements. The complexity of the individual models dictates an efficient solution scheme for the reliability analysis. Such an algorithm is developed in the present paper consisting of an adaptive response surface algorithm and an importance sampling Monte-Carlo algorithm. The response surface algorithm is based on predetermined experimental designs and facilitates the adjustment of design parameters for an optimized prediction variance in the design point region. Approaches for the consideration of multiple design points and the augmentation of the design for reduction of the prediction variance are introduced. In this paper, a reliability analysis for a tripod support structure of a Multibrid M5000 wind turbine is performed. A comparison with the target reliabilities specified in DIN EN 1990 (2002) shows that the requirements are fully met. However, the consideration of system reliability leads to the conclusion that at the end of the service life there is a significant probability of fatigue damages. The quantification of the reliability for the individual structural components for all limit states facilitates an identification of sensitive components. The results of this study can support the targeted application of monitoring systems, the optimization of the support structures and additionally highlight the need for criteria to the systems reliability.
Quasi-Static Analysis of the Multi-Component Mooring Line for Suction Anchors
Authors: Wang Li-zhong , Guo Zhen , Yuan Feng
Published: January 2011

Multi-component taut mooring line is widely used to connect the floating facility to an embedded suction anchor to provide an effective motion limit. The functions of different components should be evaluated in order to optimize its anchoring performance. This paper presents a novel two-dimensional quasi-static model, which can calculate different combinations of line type, taking into account the effects of ocean currents, soil resistance and elastic elongation of mooring line. Accurate analysis is carried out to predict the responses of multi-component mooring line during pretension and in service. Especially, when the floating facility undergoes a series of motion away from its original position, the effect of vertical offset is studied in detail. Finally, based on the presented model, the functions of different components are throughly investigated and some useful conclusions are drawn.
Fiber Augmented Steel Technology Pipe (FAST-Pipe™): An Alternative to High Strength Steel
Authors: Salama Mamdouh M.
Published: January 2011

A key imperative to the transportation of natural gas for long distance is the continued technological advances to reduce the development and life cycle cost of high pressure gas pipeline while maintaining the required high level of safety, reliability and environmental stewardship. Therefore, advances in high strength steels such as X100 and X120 have been pursued by several companies. This paper presents an alternative solution namely FAST-Pipe™ (Fiber Augmented Steel Technology - Pipe). The FAST-Pipe™ Concept involves wrapping a conventional strength steel pipe (X70) whose thickness is selected to satisfy axial and bending load requirement with dry fiberglass to achieve the pressure load requirement. The FAST-Pipe™ offers several technical and economical advantages over High strength steel concepts. The paper presents the results of the proof of concept validation program that included cost analysis and performance testing. The paper also summarizes the results of the rigorous qualification program that was implemented subsequent to the successful results of the proof of concept phase.
Ice Induced Vibration and Its Isolation of an Offshore Platform With Bucket Foundations in Marginal Oilfields
Authors: Wang Shengyong , Yue Qianjin
Published: January 2011

The economical efficiency and structural characteristics of offshore platforms with bucket foundations is an important concern in the oil/gas exploration of marginal oil fields. JZ9-3E riser platform, which was set up in the Bohai Sea, is such structure. However, very severe ice-induced vibrations were observed. A finite element model was established to analyze the structural characteristics for this platform. A good comparison between modal analysis and full-scale observation was obtained, which shows the dynamic similarity between the numerical model and the prototype platform structure. To reduce the ice-induced vibrations, a fixed ice-breaking cone was installed on this platform. Both of the FE model results and the observed data showed that the fixed ice-breaking cone can isolate the ice-induced vibrations effectively.
A Comparison of the Model and Full Scale Transom Wave of the R/V Athena
Authors: Fu Thomas C. , Terrill Eric , Fullerton Anne M. , Taylor Genevieve Lada
Published: January 2011

Over the past few years the U.S. Office of Naval Research has sponsored a series of measurements of the transom wave of the R/V Athena and of a 1/8.25-scale model (NSWCCD Model 5365) of the ship. The objectives of the testing were to characterize the free surface wave behind the ship’s transom at both model and full scale for use in identifying hydrodynamic features and for developing and validating numerical simulation tools. The focus of this paper is the comparison of these full scale and model scale measurements, specifically a comparison of the time-averaged free-surface stern wave profiles and the dominant hydrodynamic features, the rooster tail for example. Both the field measurements and the model scale tow tank measurements were made in as calm as possible ambient conditions. Full scale data was collected in the relatively protected waters of St. Andrews Bay, Florida. The winds, which typically build as the day progresses, were minimal, and it was a new moon during the test period, so tidal excursions were also minimized. While measurements were obtained for ship speeds ranging from 3.1 to 6.2 m/s (6 to 12 knots), equivalent to Froude number range based on length (47 m) of 0.14 to 0.29, respectively, the focus of the comparison is for the 0.24 Froude number (10.5 knots full scale) case. Measurements of the full scale stern wave were made by a scanning laser altimeter, while measurements at model scale were made using a traversing set of conductivity finger probes.
Engineering Design of Deepwater Free Standing Hybrid Riser
Authors: Song Ruxin , Stanton Paul , Zhou Xiaoliang
Published: January 2011

The free standing hybrid riser (FSHR) offers advantages over other field proven deepwater riser concepts for particular applications and has been used mostly off West of Africa. This concept has evolved in the last few years and now is drawing more attention in other deepwater provinces worldwide, such as the Campos Basin in Brazil and the Gulf of Mexico (GoM). It is basically a combination of steel and flexible risers with utilization of their advantages and hence offers unique features. This paper presents the engineering design and analysis aspects of deepwater FSHRs including key technologies and techniques. First of all, a general description and comparison of the FSHR system is presented. Secondly, the logical procedure for design and analysis of deepwater FSHRs is discussed and presented in more detail. Due to the complexity of FSHRs, different applicable design codes have been presented and discussed. Global configuration design with consideration of riser performance and its effect on component design is presented followed by major design considerations for individual components of the system. Thirdly, the analysis requirement and methodology is discussed in detail with focus on global response analysis, vortex induced vibration (VIV) analysis, buoyancy can (BC) VIM fatigue analysis, interface loads, and component analysis such as buoyancy can, tether chain system, top riser assembly, flexible jumper configuration, and riser base pile. The relationship between engineering design, fabrication and installation, which is of particular interests to this type of riser, is briefly discussed.
Numerical, Experimental and Full-Scaled Investigation on the Current Generation System of the New Deepwater Offshore Basin
Authors: Shan Tiebing , Lu Haining , Yang Jianmin , Li Runpei
Published: January 2011

The new deepwater offshore basin was completed in 2008 at Shanghai Jiao Tong University. The current generation system is considered to be one of the most important and challenging equipments in the basin. A lot of work has been conducted to investigate the characteristics of current generation system in the new deepwater offshore basin. Main particulars and equipments of the new basin are described in detail. Some ocean deepwater tests conducted in this new basin are also introduced. Numerical simulation, model test and full-scaled measurements in the real basin were conducted to investigate the hydraulic performances of deepwater current generation system in detail. It can be concluded that the current generation system has satisfactory performances by different methods. Uniform and constant current flows with different current velocities can be generated in this new basin. Several typical current velocity profiles can also be modeled in measuring area of the basin. It indicates that the hydraulic performances of the current generation system can satisfy requirement of offshore model tests in deepwater.
Components of a Tool to Address Learning From Accident Investigation in the Offshore Industry
Authors: Nja˚ Ove , Braut Geir Sverre
Published: January 2011

Learning is often presented as the major goal for an accident investigation process. But it often remains unclear how learning is directed or discussed in the text of investigations reports. If learning is emphasized in the report, how is the relationship between the learning processes proposed in the investigation and theories of effective learning amongst individuals, in organizations and across organizations and societal sectors? This paper presents the results of using a suggested tool to analyze the premises for learning from accident investigations. The paper compares accident investigation reports provided by different actors (operator and authority) in the Norwegian oil and gas industry covering same events.
Extreme Waves in Sea States Crossing an Oblique Current
Authors: Toffoli A. , Babanin A. V. , Ardhuin F. , Benoit M. , Bitner-Gregersen E. M. , Cavaleri L. , Monbaliu J. , Onorato M. , Osborne A. R. , Fouques J. , Moe V. , Pakozdi C. , Stansberg C. T.
Published: January 2011

Laboratory experiments have been carried out in the directional wave tank at Marintek (Norway) to study the nonlinear dynamics of surface gravity waves and the occurrence of extreme events, when the wave field traverses obliquely an ambient current. A condition of partial opposition has been considered. Tests on regular waves have shown that the current can trigger the formation of large amplitude waves. In random wave fields, however, this only results in a weak deviation from the statistical properties observed in absence of a current.
Numerical Calculation and Model Test Study on a Quay Mooring Semi-Submersible Drilling Platform
Authors: Wang Qi , Wu Xiaopeng , Lu Haining , Chen Gang , Wu Xiaoyuan
Published: January 2011

This paper introduces the study in both numerical calculation and model test of a Semi-submersible drilling platform moored along the quayside of Shanghai Waigaoqiao Shipbuilding Co. Ltd. (SWS). To obtain reliable quay mooring system for a SEMI in the out-fitting condition, complicated factors, such as a barge is applied between the SEMI and the quayside, quayside has practical limited conditions, nonlinear characteristics of mooring lines and fenders, etc., are firstly discussed. Then based on several simplifications, static analysis about different environmental conditions, normal and typhoon, are carried out, in order to design the preliminary layouts. Later on, model test with the scale of 1:50 is conducted in the basin of Shanghai Jiao Tong University (SJTU). Results between numerical simulation and model test are compared and the dynamic effect created by wave is investigated. Several principles for quay mooring layout of semi-submersible drilling platform have been concluded.
Background for New Revision of DNV-RP-C203 Fatigue Design of Offshore Steel Structures
Authors: Lotsberg Inge
Published: January 2011

The DNV-RP-C203 Fatigue Design of Offshore Steel Structures is being used by a number of different companies for fatigue assessment of different types of structures. This has resulted in questions to DNV about background for the different sections in the document. It is therefore important that the basis for this document is open to the industry. Quite a lot of the background material has also been published earlier at conferences and in journals. In some situations it has been found that the content can be improved to better suite the industry. The document is presented in an electronic version making revisions easy. Therefore it has been revised several times since the last official presentation of a revision in 2005. The present paper gives an overview of the most significant changes made in the document since the 2005 revision. Some of these changes are already included in the present version of DNV-RP-C203. The remaining changes will be included in a revision dated 2010.
Estimates of Wave Elevations Around Structures
Authors: Bratland Anne Katrine , Bo̸rresen Ragnvald , Berntsen Per Ivar Barth
Published: January 2011

When designing offshore platforms the still water air gap has to be large enough to avoid major wave-in-deck impact. Since wave elevation in harsh weather is highly non-linear, corrections to the calculated first order solution are necessary. The present method is a pragmatic approach to estimate the higher order contributions, utilizing the first order response amplitude operator and higher order wave elevations. For infinite water depth it is shown that regular wave theory is a good approximation for calculating second order wave elevation in irregular seas. So the higher order waves are calculated with regular wave theory, and the QTF and higher order terms are approximated by the first order RAO. Comparison with model test results have been performed for a GBS in moderate water depth and a semi-submersible is relatively deep water. The agreements with model tests are satisfactory.
Analysis of Full-Scale Hull Girder Loads of a Container Carrier and Its Simulation Using a Nonlinear Seakeeping Program
Authors: Lee Seung Jae , Yu Han C. , Kim Sungeun Peter , Ha Mun-Keun , Park Gun-Il , Choi Jae-Woong , Kim Munsung , Tai James S. C.
Published: January 2011

ABS, SHI, and OOCL have been conducting a project on full-scale measurement of hull stress of a container carrier since 2006. A Hull Stress Monitoring System (HSMS) was installed on an 8063 TEU container carrier recording hull girder loads and other navigation data. Vibratory responses of the hull girder were recorded at certain conditions, such as in the limited fetch storm waves in the Mediterranean Sea. The recorded data has been analyzed to determine the level of vibratory responses and the conditions in which they occurred. Since the vibratory response is superposed to the wave frequency component of the hull girder loads, it also affects the statistics of the maximum hull girder loads in waves. The effects of the vibratory responses in the long-term have been investigated for the dynamic Vertical Bending Moment (VBM) and bow acceleration. While the full-scale measurement provides valuable data for what actually happened in real vessel operations, the actual conditions can not be controlled, such as the wave environments or loading conditions. Hence, numerical calculation results are also desirable to investigate the vibratory responses under controlled conditions taking into account the elastic hull girder properties under exact conditions for validation purposes. ABS has been applying a time domain nonlinear wave/body interaction analysis program, NLOAD3D, for the assessment of the structural responses of vessels in large waves. The NLOAD3D program has been further developed to incorporate an elastic beam model to reproduce vibratory hull girder responses, with the simulations being carried out on motions and moments for selected notable events recorded during the voyages. Comparisons of the simulation and the measurement are presented.
Dynamic Analysis of Riser Release and Lowering
Authors: Atluri Sampath , Liu Nicole , Sablok Anil , Weaver Tim
Published: January 2011

Oil and gas development in certain harsh environments, such as extreme storm prone areas or arctic regions, may require the floating production platform to be designed to enable it to be released from its risers and moorings and moved out of the way of the approaching threat. Such floating platforms generally employ an underwater disconnectable buoy to support the moorings and risers after the main platform is moved away. For a deep draft floating structure, the risers can be released from their support near the top of the platform and lowered through the hull to a disconnectable buoy. In such a case, the risers can be routed through I-tubes and lowered in a controlled manner using rigging during a normal release operation. However, an emergency disconnection may require lowering of the risers without guidance of rigging. To avoid damage to the risers and the buoy during the emergency disconnection, risers can be fitted with passive damping devices to limit the lowering riser speed. This paper presents the numerical efforts to define the emergency riser release and lowering procedure. CFD simulations were performed to evaluate the hydrodynamic behavior of a disconnected riser in a flooded I-tube with the controlling devices attached to the risers. Applying the CFD results, riser lowering performance was computed using finite element analysis method. Primary parameters that affect flexible riser behavior, including stress level and curvature, are identified and sensitivity study results are presented. This paper concludes that a safe and controlled riser release procedure and system is achievable.
Risk and Reliability Based Fitness for Service (FFS) Assessment for Subsea Pipelines
Authors: Bai Yong , Mustapha Mohd Ashri B. , Zhang Fangyuan , Shao Vincent Hui
Published: January 2011

The risk and reliability based fitness-for-services (FFS) assessment addressed in this paper is a quantitative risk assessment (QRA) based FFS study on subsea oil or gas pipelines. The main purpose of QRA is to determine the target reliabilities for different pipeline segments. And then, a structure reliability analysis (SRA) method is used to calculate the maximum safe operating pressure, which indicates the pipeline retaining pressure capacity. It has been revealed that the target reliability or target safety level should reflect the consequences of failure, inspection and monitoring scheme etc. But, in the traditional FFS assessment (e.g. B31G and DNV RP F101), the identification of pipeline target reliability is merely based on qualitative judgments and experience. In this paper, however, a quantitative risk assessment will be performed based on abundant data from pipeline inspection and monitoring records, pipeline environmental impact assessment (EIA) study report, pipeline corrosion study report, pipeline emergency response scheme and anything else which can affect the pipeline failure consequences. An example of pipeline FFS assessment performed at four levels has revealed that the risk and reliability based FFS results have much better consistency to the reality.
Seismic Analysis for the Subsea Pipeline System
Authors: Arifin Rosman B. , Wan M. Yusof Wan M. Shafrizal B. , Zhao Pengfei , Bai Yong
Published: January 2011

Seismic activity in Malaysia is very low as earthquakes are infrequent in this region. The strongest measured earthquake magnitude record in this region since 1978 was 4, which had a very low impact on the integrity of pipelines system in Malaysia. Although this is the case, there exists seismic events in the neighbouring regions and such events may impact the operability, stability and safety of Malaysia submarine pipeline systems. Based on this, a pipeline integrity analysis has been carried out to check the pipeline integrity under the seismic influence. The purpose of the analysis includes: • To calculate earthquake response for three PCSB PMO main export pipelines — for each pipeline both buried and unburied conditions will be taken into account. • To understand the characteristics of buried and unburied pipelines under strong earthquakes affecting Malaysia waters. • To determine the peak ground acceleration (PGA) the pipelines can withstand. • To determine the largest permanent ground deformation (PGD) the pipeline can withstand. • To estimate the impact of the metal loss on the pipeline integrity. • To assist PETRONAS to prepare for such severe earthquakes. Two typical methods have been employed to make the analysis: • Time history method is used to calculate both buried and unburied pipeline response. Two typical seismic wave records have been used in the analysis, which will give a better estimation of the pipeline response under the seismic wave impact. • Soil-pipe element method is used to simulate the behavior between the soil and buried pipeline system. Based on choosing the suitable experimental equations, this method can simulate the soil behaviour accurately. This paper discusses results of the seismic analysis. Based on the analysis results, the pipeline system will be safe under the seismic wave impact. More attention should be given to fault hazard, as the pipeline system will been failed under the fault impact. Finally, the metal loss will be taken into consideration, for the pipeline stress will be much higher due to great metal loss. All those analysis results will be further utilised to estimate the pipeline response in the case of the earthquake.
On Choice of Finite Element Type for the Filled Bodies in Umbilicals for Deep Water Application
Authors: Ye Naiquan , Gjo̸steen Janne K. O̸. , Sævik Svein
Published: January 2011

Filled bodies are often built into umbilicals to support other key components such as tubes and electric elements. These bodies play an important role in transferring the contact load between bodies when the structure is loaded. The geometrical profile can be arbitrary to fill the voids within the umbilical cross section and this causes difficulties with respect to implementation into a general finite element model. Common practice is to omit the filled bodies in cross section modeling by enabling direct contact between components. However, it has been found that the friction stress will be over estimated by this method and cause over-conservative fatigue calculations. This may be critical specially for deep water dynamic umbilicals and more accurate estimation of the friction stress is therefore needed. UFLEX2D is a non-linear finite element computer program for stress analysis of complex umbilical cross sections, see [3] and [5]. The model can handle arbitrary geometries wound in an arbitrary order including filled bodies. Contact elements are used to handle the contact between bodies due to external loading. Thin-wall shell elements were used to model the steel tubes while beam elements were used for the filled bodies in the earlier version of UFLEX2D. A beam element is treated as a rigid body incapable of deforming under external loading. It has been found that the formulation of the beam element for the filled bodies yields relatively large contact pressure for the neighboring element due to its rigidity. As a consequence, friction stress owing to the contact pressure is overestimated by the choice of the beam element for the filled bodies, however, it will be smaller than the direct contact modeling technique mentioned above. A new element type, i.e. a beam-shell element, has been developed to represent the filled bodies so as to improve the contact formulation between the filled bodies and the other surrounding structural elements. Unlike the beam element, the beam-shell element is able to deform, therefore the contact area is varying while the external load updates. The friction stress will be accordingly affected by the redistribution of the contact pressure on an updated contact area. The paper outlines how different implementations of the filled bodies will affect the distribution of the contact pressure as well as the friction stress under cyclical loading. The effect of the original contact area, as well as the development of the contact area is also a part of the study fot the three alternative models investigated.
To Simulate the Stability of Undersea Pipeline Under Typhoon Wave Action by Numerical Analysis
Authors: Chien Lien-Kwei , Tseng Wen-Chien , Chuang Sheng-Tse
Published: January 2011

When the typhoon comes, the undersea pipelines usually are caused the destory, lateral displacement and floating easily by wave loading. Therefore, the main reason of the unstable seabed may be the typhoon wave loading. This study from the ocean geotechnical viewpoint, the study area of undersea gas pipeline route from Taoyuan to Taichung in western coast of Taiwan was selected. In this study, further by using the GeoStudio QUAKE/W software program to simulate the wave laoding. The marine meteorological data including strength parameters was collected and also jointed with wave theory. At the same time, under the wave action condition, pipeline weight and embedded depth are also discussed. This study assesses the influences of the undersea pipeline stability, and the purpose is to decrease structure damage. Based on the results of theoretical calculation and numerical simulation, it can be found the undersea pipeline induced by periodic wave loading occur the relative displacement maximum up to reach about 0.93.
Blind Prediction of Ship Maneuvering by Using Support Vector Machines
Authors: Luo Wei-lin , Zou Zao-jian
Published: January 2011

Support Vector Machines (SVM) based system identification is applied to predict ship maneuvering motion. Different from the prediction methods based on the explicit mathematical model of ship maneuvering motion, the black-box model of ship maneuvering motion is constructed and used to predict ship maneuvering motion. With the rudder angle and the variables of maneuvering motion as inputs and the hydrodynamic forces as outputs, the complicated nonlinear functions in the Abkowitz model are identified; and the surge force, sway force and yaw moment are predicted blindly by using the functions identified. Taking turning test as example, with the rudder angle as inputs and the maneuverability parameters of turning circles as outputs, the input-output mappings are identified and the maneuverability parameters such as the advance, the transfer and the tactical diameter are also predicted blindly by using the identified mappings.
On Sea Experiment of a Hybrid SPAR for Floating Offshore Wind Turbine Using 1/10 Scale Model
Authors: Utsunomiya Tomoaki , Matsukuma Hidekazu , Minoura Shintaro , Ko Kiyohiko , Hamamura Hideki , Kobayashi Osamu , Sato Iku , Nomoto Yoshihisa , Yasui Kentaro
Published: January 2011

This study aims at development of a cost-effective floating offshore wind turbine. The proto-type model considered herein is composed of 1) 2MW horizontal-axis wind turbine (HAWT) of down-wind type, 2) steel mono-tower with 55m hub height above sea level, 3) steel-prestressed concrete (PC) hybrid SPAR-type foundation with 70m draught, and 4) catenary mooring system using anchor chains. In order to demonstrate the feasibility of the concept, on-sea experiment using a 1/10 scale model of the prototype has been made. The demonstrative experiment includes 1) construction of the hybrid SPAR foundation using PC and steel as same as the prototype, 2) dry-towing and installation to the on-sea site at 30m distance from the quay of the Sasebo shipbuilding yard, 3) generating electric power using a 1kW HAWT, and 4) removal from the site. During the on-sea experiment, wind speed, wind direction, tidal height, wave height, motion of the SPAR, tension in a mooring chain, and strains in the tower and the SPAR foundation have been measured. Motion of the SPAR has been numerically simulated and compared with the measured values, where basically good agreement is observed.
Fatigue Damage Estimation of Stinger Main Hinges Subject to Wave Loadings
Authors: Zhang Xiangfeng , Zhang Wenshou , Yue Qianjin , Li Xin
Published: January 2011

The laying of subsea pipelines is usually carried out by means of S-lay technology. As stingers become longer and longer, wave-induced fatigue damage problem for the stinger main hinges connecting both the stinger and the stinger adjustment frame fore leg to the vessel stern via a common shaft may have to be taken into consideration. Usually, there is a structural health monitoring system (SHMS) to be installed on the stinger for performance assessment. A procedure for assessing long-term wave-induced fatigue damage to a stinger is thus presented in this paper with continuum damage mechanics (CDM)-based fatigue damage assessment method. By taking the stinger of DPV7500 being built for Chinese Offshore Oil Engineering Corporation (COOEC) as an example, a structural health monitoring-oriented finite element model of the stinger is established. Water tank experiments were conducted to measure the roll, pitch and heave motion responses of the vessel model for different wave height, wave period and directions. The measurement data are then used to carry out the stress analyzes of the stinger to identify stress characteristics at hot spots of the stinger. The accumulative fatigue damage at hot spots during the stinger design life is finally evaluated using a CDM-based fatigue damage evolution model.