bluuebunny/crossref_metadata_2025 huggingface dataset:
An Efficient VOF-Based RANS Method to Capture Complex Sea States
Authors: Woeckner Katja , Drazyk Withold , Rung Thomas
Published: January 2011

Viscous seakeeping and manoeuvring simulations are becoming more important for an investigation of intact and damage conditions of ships exposed to extreme sea-states. The computational effort for RANS-based viscous seaway simulations is still prohibitive and reduces the possible fields of industrial applications. The limitations are associated to cumbersome grid requirements which restrain the flexibility and enhance the computational costs. The requirements follow from the aim to accurately predict the wave propagation towards the floating object and concurrently suppress wave reflections at the outlet boundary. To overcome these difficulties, a simple viscous/inviscid-coupling approach is suggested. Therein, the viscous RANS method is implicitly forced to comply with a prescribed invis-cid solution towards the far-field boundaries. Employing consistent boundary conditions at all far-field boundaries, the method facilitates the use of small domains and allows to investigate the behaviour of floating objects exposed to time-variable wave-field directions. Selected 2D and 3D examples are presented to demonstrate the capabilities of the approach.
Response of Pipelines Under VIV: An Experimental Investigation
Authors: Soni Prashant K. , Larsen Carl M.
Published: January 2011

Pipelines laid on an uneven bottom often have free spans. For cases with long spans, one may have several modes and eigenfrequencies that can be excited by vortex shedding. Furthermore, due to the sag effect of a long free-span, the dynamic properties are different in vertical and in horizontal directions. This causes a complex response pattern in the cross-flow (CF) and in-line (IL) directions. From previous research we know that pure IL response at relatively low current velocities may significantly contribute to fatigue damage. This response type must be studied in addition to the combined IL and CF response. The objective of this paper is to present experimental results from flexible beam experiments where both response types are studied, as well as to present results from an empirical response model for the same cases. The empirical model is based on two types of experiments. The first set of experiments were conducted with a flexible pipe for both single and double span configuration. Pure IL and combined IL and CF motions were observed. In the second set of experiments, forces on a rigid cylinder were measured under forced motions in a current. The motions were found from measurements of cross section in the flexible pipe tests. Hydrodynamic coefficients such as drag, added mass, excitation and damping force coefficients were found and then applied in the empirical response model. In the present paper the results from the flexible beam experiments are presented and also compared with the results from the empirical response model. The results so far are encouraging, but further work and more data are needed in order to have a general and robust response model for combined CF and IL VIV.
Analytical Formulation of Distributed Buoyancy Sections to Control Lateral Buckling of Subsea Pipelines
Authors: Antunes Bruno Reis , Solano Rafael Familiar , Vaz Murilo Augusto
Published: January 2011

Subsea pipelines designed to operate under high pressure and high temperature (HP/HT) conditions tend to relieve their axial stress by forming buckles. Uncontrolled buckles can cause pipeline failure due to collapse, low cycle fatigue or fracture at girth welds. In order to control the lateral buckling phenomenon, a methodology was recently developed which consists of ensuring regular buckle formation along the pipeline. Distributed buoyancy is one of the most reliable initiation techniques utilized for this purpose which have been recently applied in some projects. The behavior of pipeline sections with distributed buoyancy is normally evaluated by Finite Element Analyses (FEA) even during preliminary design when analytical models could be adopted. FEA are also utilized in order to support reliability calculations applied within buckle formation problems. However, the referred analyses are usually time-consuming and require some experience to provide good results. This paper presents an analytical formulation for a pipeline section with distributed buoyancy, which can be utilized during preliminary design in order to evaluate the influence of buoyancy sections over buckle shape, feed-in length, tolerable Virtual Anchor Spacing (VAS), etc. Regarding buckle formation, this paper also presents a methodology to determine an expression for the critical buckling force to be used as part of the limit state function in reliability analyses, which combines the results obtained from the referred analytical formulation with Hobbs infinite mode.
Design Optimization of Top-Tensioned Risers for Deepwater HPHT Applications: Part 1
Authors: Xu Lixin , Stanton Paul
Published: January 2011

Dry-tree solutions with top-tensioned risers (TTRs) have been successfully used with floating production systems (FPS), such as Spars and TLPs, in a wide range of deepwater applications. Both single-casing and dual-casing top-tensioned risers are field-proven in existing field developments. The top-tensioned risers bring technical advantages and operational cost benefits. However, recent oil and gas developments that have high pressure and high temperature (HPHT) in combination with severe environmental loads push the design limits of conventional steel pipes in deepwater risers. High-strength steel pipes are therefore considered for risers for both technical and economic reasons. This paper discusses the impact of the above requirements on design of top-tensioned risers, and proposes feasible design concepts for top tensioned risers with extremely high pressure requirements. Part I of the topic here addresses strategies of top-tensioned riser sizing and weight management, and design considerations for TTR specialty joints. Part II of this topic will follow for top-tensioned riser tensioning system configuration and tension performance optimization, as well as coupled motion compensation on the host platform. The objective of the study that forms the basis for this paper is to provide top-tensioned riser system configurations that meet the challenges of the extremely high operational pressure and environmental loads in deep and ultra-deep waters.
Strength Loss of SS Platform Column Due to Ship Collision
Authors: do Amaral Amante Diogo , Rossetto Renan M. , Estefen Segen F.
Published: January 2011

Despite the efforts to reduce ship accidents, the collision between supply vessels and offshore platforms continue to happen. The aim of the present paper is to evaluate the ultimate buckling residual strength of a typical semi-submersible platform column damaged by a supply vessel collision. DNV recommendations are adopted for the sideways collision and either bow or stern collision, corresponding to a supply vessel of 5,000 ton displacement with impact velocity of 2 m/s. Additionally, some cases considering the tendency in the world market for supply vessels with larger dimensions and more powerful propulsion are considered. This brings additional questions about the structural integrity of the floating unit represented by the column residual strength able to resist the deck loading up to the repair work to be performed. In this paper the program ABAQUS was used to carry out the dynamic collision simulation. The buckling analysis was validated using a finite element model considering geometric and material nonlinearities as in previous correlation studies with small scale experiments. Residual strength results from the damaged column are compared with the ultimate strength of equivalent intact column to estimate the safety margin associated with the column structural capability after supply vessel collision.
CFD Simulation and Wind Tunnel Investigation of a FPSO Offshore Helideck Turbulent Flow
Authors: de Carvalho e Silva Daniel Fonseca , Pagot Paulo Roberto , Nader Gilder , Jabardo Paulo Jose´ Saiz
Published: January 2011

The offshore helideck wind flow is usually subject to many interferences. The helideck airspace velocity and turbulence fields are important issues to promote safe helicopter take-off and landing operations. The current work brings some CFD results of a helideck wind flow 3D-field defined by the local conditions and constrained by the FPSO structure. A discussion about the chosen CFD boundary conditions is also presented. These CFD results are compared with the wind tunnel model-scale velocity and turbulence measurements. The wind tunnel measurements were performed with use of two different techniques: Particle Image Velocimetry (PIV) and Constant Temperature Anemometry (CTA). The British standard CAP437: Offshore Helideck Design Criteria is examined and suggestions are made herein. The CFD simulations were conducted using the ANSYS CFX software.
Consequence Analysis of a Liquefied Natural Gas Leakage
Authors: Natacci Faustina Beatriz , Ikeda Nilton Hiroaki , Ramos Martins Marcelo
Published: January 2011

Each and every quantitative risk assessment comprises some basic activities that have to be developed to allow the quantification of the risks involved in the operation of a system or process. Basically, it must be estimated the likelihood of the identified undesired events as well as the magnitude of their consequences. When analyzing the risks in the operation of a ship, the same process has to be followed. For each specific phase of the ship mission, all undesired events must be correctly determined and evaluated. Many different types of undesired events must be investigated, such as: collision, grounding, fire, and explosion. There are many techniques and much work involved in the estimation of the likelihood of the events. The same occurs for the evaluation of their consequences. The purpose of this paper is to study the consequences of a liquefied natural gas (LNG) leakage from the rupture of a pipeline from an LNG vessel during cargo loading at a terminal in the Brazilian coast. Once defined the total leaked quantity, a software will be used to calculate the consequences. The main idea is to identify all possible consequences and verify their magnitudes on the coast. This is not a simple task because it requires the comprehension of the development of the phenomena involved after the leakage. There is also the need of the identification of many variables, including the atmospheric conditions and the ignition sources, in order to verify the extent of possible cascading events. It will be taken special attention to consequences to human beings as a result of exposure to heat radiation effects from possible fires and explosions. As a preliminary study, where the likelihood of the events will not be estimated, the final objective is to use the obtained results to predict preventive and mitigating measures, in order to reduce the consequences to people on the coast.
A New Model for Analyzing Collision of Ships
Authors: Isshiki H. , Yoon B. S. , Cho S. R.
Published: January 2011

In the present paper, the bow of the striking ship is assumed to collide the midship part of the struck ship. In the previous model, the striking ship is approximated by a lumped mass system, and the struck ship by one mass and one spring system. In the present model, the struck ship is replaced by a system composed of rigid bars and elasto-plastic hinges. This model not only can express the response of the struck ship more reasonably, but also dose not require much time for numerical simulation. Some numerical results are shown to show the effectiveness of braking panels.
Pattern Studies of the Strain Distributions for Detecting Pipe Wrinkling
Authors: Chou Z. L. , Cheng J. J. R. , Zhou Joe
Published: January 2011

As both the onshore and offshore pipeline constructions push further into higher risk terrains, such as geologically unstable terrain and Arctic region, the risk of local buckling failure (wrinkling) for these buried pipelines has been increasing gradually. However, previous methods used to prevent the buried pipelines from buckling failure are expansive, time consuming, and unreliable. Therefore, to overcome these problems, a reliable method to predict pipeline wrinkling has been proposed. The method can provide active warning for pipeline wrinkling through a decision-making system (DMS). The DMS was designed to identify the strain distribution patterns and their development on the critical pipe segments for early detecting the onset of pipe wrinkling. To conduct the reliable DMS, studies of the strain distribution patterns on the line-pipes during pipe buckling are very important. In this paper, the strain distribution patterns of various line-pipes were presented. These line-pipes have different material and geometric properties, loading conditions, and manufacturing conditions. A total of 32 sets of experimental results and 72 sets of finite element analysis (FEA) along with parametric studies were included in the study. The study concluded significant behavioural characteristics revealed on the strain distribution patterns during pipe buckling and important parameters affecting these strain patterns. For practical application, three thresholds of the strain distribution patterns were proposed. Furthermore, the optimal positions and spacing of the strain measurements for early detecting pipelines wrinkling were discussed as well.
Study on Revitalization Incorporating Improvement of Social Recognition and Attractiveness of Public Marinas
Authors: Hanai Kenta , Masuyama Miki , Kondo Takeo , Yamamoto Kazukiyo , Noto Keiichi
Published: January 2011

Although sea bathing is a typical marine recreation, the annual number of people participating in sea bathing has drastically declined from 120 million people (i.e., equivalent to the total population of Japan) at its peak, to 20 million people. Similarly, the ownership of pleasure boats, which once peaked at 440,000, has been declining over the years. Marinas are particularly important for their function as centers of sport fishing, which is the second most popular marine recreation after sea bathing. There are about 520 marinas in Japan, of which about one quarter are public marinas. The rise and fall of public marinas greatly affects not just the decline of the user population but also the economic activity of the surrounding regions. The present study focused on public marinas, which hold central importance among marine recreational facilities. Measures for revitalizing public marinas are discussed from a comprehensive perspective.
Numerical Analysis of 4-Piles Model in Lateral Spreading of Liquefied Ground
Authors: Shao Qi , Tang Xiaowei , Bai Xu
Published: January 2011

Lateral spreading of liquefied ground due to strong earthquakes frequently causes serious damage to multi-piles foundations. The relative displacement of flowing liquefied soil to piles affects the lateral force on piles and the failure of piles. In this study, two 4-piles models in liquefiable soil are simulated numerically by the three-dimensional dynamics FE-FD coupled method in which an fluidal elasto-plastic constitutive model is adopted to describe the saturated soil; the analysis is taken onto the reaction of front and back piles in laterally spreading, and the relationship between the relative displacement of flowing liquefied soil and the reaction of piles is also discussed.
Significance of Lu¨der’s Plateau on Pipeline Fault Crossing Assessment
Authors: Odina Lanre , Conder Robert J.
Published: January 2011

When subjected to permanent ground deformations, buried pipelines may fail by local buckling (wrinkling under compression) or by tensile rupture. The initial assessment of the effects of predicted seismic fault movements on the buried pipeline is performed using analytical approaches by Newmark-Hall and Kennedy et al, which is restricted to cases when the pipeline is put into tension. Further analysis is then undertaken using finite element methods to assess the elasto-plastic response of the pipeline response to the fault movements, particularly the compressive strain limits. The finite element model is set up to account for the geometric and material non-linear parameters. The pipe material behaviour is generally assumed to have a smooth strain hardening (roundhouse) post-yield behaviour and defined using the Ramberg-Osgood stressstrain curve definition with the plasticity modelled using incremental theory with a von Mises yield surface, associated flow rule and isotropic hardening. However, material tests on seamless pipes (X-grade) show that the stress-strain curve typically displays a Lu¨der’s plateau behaviour (yield point elongation) in the post-yield state. The Lu¨der’s plateau curve is considered conservative for pipeline design and could have a significant impact on strain-based integrity assessment. This paper compares the pipeline response from a roundhouse stress-strain curve with that obtained from a pipe material exhibiting Lu¨der’s plateau behaviour and also examines the implications of a Lu¨der’s plateau for pipeline structural integrity assessments.
Onset of Scour Below Pipeline Under Combined Waves and Current
Authors: Zang Zhipeng , Cheng Liang , Zhao Ming
Published: January 2011

Onset of scour below a submarine pipeline under waves and current is studied experimentally and numerically in this paper. A series of laboratory tests were conduced in a mini O-tube (MOT) facility to investigate the onset conditions of scour below a pipeline subject to oscillatory flows superimposed on a steady current. The effect of parameter α, which is defined as α = Uc/(Uc+Uw), on the onset of scour under combined waves and current was investigated and a simple empirical formula for evaluating the criterion for onset of scour is presented. The numerical calculations were carried out to simulate the onset of scour using a calibrated numerical model. The pressure drop coefficient over a pipe under combined waves and current was studied. The effectiveness and accuracy of the empirical model was calibrated by the numerical results.
Investigation of Wave Conditions in the Paranagua´ Estuarine Complex in the South of Brazil
Authors: Nazarpour Farhad , Mayerle Roberto
Published: January 2011

This paper summarises results of investigations aiming at the improvement of the understanding about the wave conditions in the Paranagua´ Estuarine Complex (PEC) in the South of Brazil. The investigations were carried out in the framework of a joint-research project funded by the German Ministry of Education and Research and the Ministry of Science and Technology in Brazil. In this study a phase-averaged wave model was set-up and applied to the study area. The relevance of the main processes affecting wave generation and dissipation were investigated. Focus was given to the wave conditions in the vicinity of the harbour some 25km within the PEC. The fetch was found to have a major effect on wave generation in the study area. Significant wave heights up to about 0.6m resulted near the harbour during storms. The results obtained helped in advancing the development of the coupled process-based models for simulation of flow, waves and sediment transport in the PEC. It was found that although currents have a certain influence on the wave heights, the effect of the tidal variation resulted more significant. Moreover waves were found to affect the current velocities in shallow water areas and should therefore be included for enhancing the predictions of sediment transport rates particularly for more adverse wind conditions.
Risk Based Inspection (RBI) for Subsea Equipments
Authors: Bai Yong , Ashri Mohd , Badaruddin Mohd Fauzi , Bai Xu , He S. L.
Published: January 2011

The fleet of subsea systems, such as pipelines, trees and manifolds etc is at present rapidly increasing. This paper presents a risk based inspection planning approach that is new for subsea equipments. Very few publications on RBI of subsea equipments exist and have been actually applied due to the complexity of subsea components. In this paper, failure modes are described, offshore reliability database is used and risk analysis is performed taking into account the consequences of failure of equipments mainly in terms of Asset (Loss of production, Unavailability, Costs of repair). Risk level and corresponding inspection effort are estimated. An overall inspection plan is then provided for all structural components of subsea equipments: pipelines, trees and manifolds. Such a methodology has the benefit to rank the components and results in optimization of the inspection and maintenance effort.
Hydrodynamic Analysis of Two Side-by-Side Moored Floating Bodies
Authors: Hong D. C. , Kim Y. Y. , Han S. H.
Published: January 2011

The hydrodynamic interaction of two bodies floating in waves is studied. The two-body hydrodynamic coefficients of added mass, wave damping and exciting forces and moments are calculated using the irregular frequency free radiation-diffraction potential solution of the improved Green integral equation associated with the free surface Green function (Hong 1987) according to the conventional two-body analysis. It is well known that the conventional two-body potential solution with usual grid fineness largely overestimates the hydrodynamic coefficients at and near the resonance frequency of the free surface in the gap between two floating bodies moored side-by-side in close proximity (Huijsmans et al. 2001, Hong et al. 2005). The two-body diffraction problem has been solved by both the conventional two-body analysis without damped free surface condition and a boundary matching method with and without damped free surface condition. Numerical results of the wave exciting force coefficients of two identical caissons floating side by side obtained by the two methods have been presented and the discrepancies between them have been discussed. Particular attention is paid to the wave elevation in the gap at the resonance frequencies. Amplitudes and phases of the scattering wave elevations in the gap at the first three free surface resonance frequencies computed by the boundary matching method without damped free surface condition have been presented. It has also been shown that the unrealistic wave elevation due to the resonance of the free surface in the gap can be reduced by imposing the damped free surface condition upon the flow in the gap as used in the oscillating water column hydrodynamics (Hong et al. 2004).
Design and Structural Analysis of Mono Pile Foundation for Offshore Wind Turbines
Authors: Zhang Jianhua , Wang Zhenqing , Zhang Liang , Sun Ke , Hao Jun
Published: January 2011

Offshore wind energy offers a huge potential for expansion of renewable energy in the world. However, placement of wind turbines in harsh offshore environments is an engineering challenge, which requires development of suitable foundation designs. This paper shows different foundation types which are decided by different cases of the seabed. The mono pile foundation for 1.5MW offshore wind turbine is designed for Bohai Bay in China considering the soil and seabed condition. A three dimensional (3D) finite element model of mono pile is established to analyze horizontal ultimate bearing capacity, stress and deformation under lateral loads. Through the modal analysis, the natural frequencies of the mono-pile are given. Results show that the designed mono pile can effectively preclude resonance with the wind turbine. Dynamic responses under wave and seismic loads are analyzed by transient analysis method. And at same time, dynamic amplification factors of stress and deformation are studied. The paper reaches the conclusion that the dynamic effect must be attached importance in the design. Moreover, based on the theory of stability, the simplified method to assess the ultimate buckling moment of the mono pile is put forward. Comparisons are also made with results calculated by codified rules of DNV and ABS and Finite Element Method. Besides, fatigue analysis is carried out according the codified rules of API. The numerical results demonstrate that the design of mono pile is reasonable and reliable. The research results can provide the reference for practical engineering in China.
Elastic Large Deflection Behavior of Plates With Partially Rotation-Restrained Edges
Authors: Paik Jeom Kee , Kim Do Kyun , Lee Hoseong , Shim Yong Lae
Published: January 2011

The edge condition of the plating in a continuous stiffened-plate structure is neither simply supported nor clamped because the torsional rigidity of the support members at the plate edges is neither zero nor infinite. In a robust ship structural design, it is necessary to accurately take into account the effect of the edge condition in analyses of plate behavior. The aim of this study is to investigate the elastic large deflection behavior of plates with partially rotation-restrained edges in association with the torsional rigidity of the support members and under biaxial compression. An analytical method was developed to solve this problem using the nonlinear governing differential equations of plates. The validity of the developed method was confirmed by the comparison with nonlinear finite element method solutions with varying values for the torsional rigidity of the support members, plate aspect ratio, and biaxial loading ratio. The developed method was found to give very accurate results for the large deflection analysis of plates with partially rotation-restrained edges, and was proved very useful for the robust design of ship structures.
The Method for Improving the USBL Positioning System
Authors: Min Yu
Published: January 2011

This paper addresses a problem of estimating the precision phase-shift between the transducers of an Ultra short baseline (USBL) array. Due to fact that the performance of the traditional USBL system would evidently decline as the position error increases with the range, the paper at first proposed a high-precision positioning algorithm applied to an improved array to overcome this problem. Besides, employing a least-squares method, the additional phase shift between the transducers are also considered to be determined experimentally by rotating the USBL array in an acoustic test tank, which furthermore reduces the phase shift measuring error. Some trials results show that the proposed high-precision algorithm with improved array can be achieved with good accuracy, as well as the alignment phase shift offset.
Fatigue Safety Assessment of LNG Carrier Based on Reliability Analysis
Authors: Xiao Taoyun , Xu Shuai , Liu Jingxi
Published: January 2011

The procedure of reliability-based fatigue analysis of LNG carrier of membrane type under wave loads is presented. The stress responses of the hot-spots in regular waves with different wave heading angles and wave length are evaluated by global ship FEM. Based on the probabilistic distribution function of hot-spots’ short-term stress-range using spectral-based analysis, Weibull distribution is adopted and discussed for fitting the long-term probabilistic distribution of stress-range. Based on linear cumulative damage theory, fatigue damage is characterized by an SN relationship, and limit state function is established. Structural fatigue damage behavior of several typical hot spots of LNG middle ship section is clarified and reliability analysis is performed. It is believed that the presented results and conclusions can be of use in calibration for practical design and initial fatigue safety evaluation for membrane type LNG carrier.
A Global Migration Risk to Partially Constrained Long Pipelines Subject to Localized Thermal Gradient Cycles
Authors: Wang Yunxiao Nick , Maschner Emil A. , Hayes Rob
Published: January 2011

In recent years the progressive migration of pipelines along their length when subject to routine cyclic operation has become a serious design problem for a number of deepwater developments. Due to parameter uncertainties and need for simplified modelling assumptions a high level of uncertainty can exist in regard to the final design outcome. This often necessitates a ‘wait and see’ approach in regard to installing costly pipe anchors or evaluating the risks imposed by displacement loads at or in the vicinity of vulnerable structures located along the flowlines. This paper addresses a recently discovered phenomenon identified during studies of the global movement of long pipelines. These flowlines may be seated on variable slopes with significant routine thermal heat-up/cool-down gradients from both general production and shutdown dieseling operations. Traditional global mitigation involves short or non-cyclically-constrained pipelines which move towards their cold end or down seabed slopes. The topic described within this paper is for long partial or cyclically constrained pipelines which are capable of moving towards either end of the pipeline if subject to exceptional loading conditions. In this paper the new type of pipeline global migration phenomenon or ‘caterpillar-type’ locomotion is discussed. An analytical method has been developed to capture the mechanism and highlight its sensitivity in regard to changes in design parameter. Worked examples from design projects are given and the overall findings discussed. The phenomenon and the design solutions presented should be topical to current deepwater pipeline designs within the oil and gas industry.
Retrofittable External Hoop Strain Sensors to Monitor Changes in Internal Pressure, During Hydrate Blockage Remediation, in a Deep-Water Flowline
Authors: Podskarbi Mateusz
Published: January 2011

This paper will describe the first use of a retrofit non-intrusive pressure measurement system to monitor effects of remediating a hydrate blockage in a deep-water flowline jumper. The system was developed in response to a requirement to monitor pressure on the jumper in order to aid in gas hydrate remediation and to monitor the effects of the remediation processes to clear the blockage. An ROV-deployed non-intrusive hoop strain monitoring system (subC-pts*) was designed for clamping to the flowline, which had unknown internal pressure distribution, in order to report hoop strain changes, therefore derive the internal pipe pressure during intervention and remediation. In addition to the requirement for permanent storage of data, Schlumberger’s design included a high intensity LED mounted in the wall of unit, indicating the value of hoop strain on the subC-pts. Four self-contained systems were supplied. Each stand-alone sensor comprised an optical interrogation system, battery pack, data storage and real-time LED. The subsea optoelectronics were contained in a pressure-sealed housing secured to a composite structure containing fiber-optic strain sensors. The housing was removable from the sensor unit, for maintenance purposes, and was connected to the composite structure by an optical jumper cable. The systems were ROV-deployed onto a 30m length of jumper, at depths greater than 1000m. The measurement of hoop strain using highly linear strain sensors, and the deduction of pressure variation is examined. Focus is given to the novel aspects of the technology, and to areas where further improvements can be made, particularly with a view to developing alternative potential problem solving applications.
Prediction of Fatigue Life of Shallow Water Offshore Platforms Using Spectral Fatigue Analysis Method
Authors: Feng Qin , Large Richard
Published: January 2011

Spectral fatigue analysis approach is highly recommended for fixed offshore platform design and reassessment by API. This method is a computationally efficient method, being able to handle the random nature of environmental ocean wave conditions during calculating wave loads on the offshore platforms and subsequent structural responses. However, its fundamental theory is based on the assumption of linearity of both structural system and wave loading mechanism. Although this method is critically appropriate to be applied in offshore platform design and fatigue assessment for deep water scenarios where wave and force nonlinearities are not very severe, it has still been widely utilized for the design and assessment of shallow water platforms in offshore industry without carefully considering possible errors caused by strong nonlinear factors between ocean waves and forces. The source giving rise to the errors is because of the difficulties in choosing suitably correct wave heights for a series of wave periods required for producing transfer functions between sea state spectra and structural response spectra. Therefore, the studies to justify the possible errors of the spectral fatigue analysis method for shallow water platforms have been provoked. This paper presents the results of the studies of investigating the errors from currently existing spectral fatigue analysis method. A new technical approach that can reduce the errors in the spectral fatigue analysis of shallow water platforms is introduced. The proposed technical approach is mainly focused on producing realistic transfer functions between sea state spectra and structural response spectra, which can reasonably reflect the individually local sea state data by using wave height-period joint probability density function. Hence the fatigue damage and life at the tubular joints of offshore platforms can be more precisely predicted. The spectral fatigue analysis of a practical shallow water jacket platform in the recent platform design project has been performed using the proposed approach and the results are discussed.
Renewal Scantling Evaluation for FPSO Conversions Considering Pitting Corrosion Effects
Authors: Sun Haihong , Wang Xiaozhi , Montaruli Bret C. , Thayamballi Anil
Published: January 2011

When considering an existing tanker for conversion to an FPSO with an expected service life of 15 or more years, a comprehensive reassessment of the hull structure should be conducted and appropriate corrosion margins for the hull girder and local scantlings should be established. Among all structural deteriorations incurred by trading tankers with an age of 10 years or more, corrosion wastage represents the most dominant one. There are two types of corrosion found to occur most frequently in aging tankers, namely general corrosion and pitting corrosion. In the case of general corrosion, the yielding and buckling strength of plating and structural members can be readily determined by deducting the corrosion wastage from the as-built scantling values. However, the determination of the strength reduction due to pitting corrosion is more difficult and complex, and the use of nominal loss of material may be insufficient. This paper discusses the findings from the authors’ investigations of a number of different pitting corrosion distributions, and proposes recommendations for considering pitting corrosion effects during the establishment of renewal scantlings at the time of conversion.
Evaluation and Development of Electrodes for Wet Welding of Structural Ship Steels
Authors: Santos Valter R. , Monteiro Mauri´cio J. , Assunc¸a¯o Fernando C. R. , Bracarense Alexandre Q. , Pessoa Ezequiel C. P. , Marinho Ricardo R. , Domingues Jose´ Roberto , Vieira Leonardo A.
Published: January 2011

To better understand the behavior of some commercial wet welding electrodes down to 20 m equivalent water depth as well as to develop a new electrode, a research program was initiated in 2007. This depth is considered the maximum expected in the in situ repair of structural parts of floating production units. The weld metal evaluation was done by microstructural characterization, Vickers hardness, Charpy and tensile tests, chemical analysis, and diffusible hydrogen measurement. The influences of pressure on the mechanical properties of the weld metal are presented and discussed on the basis of chemical composition, microstructure and porosity. The electrode under development showed promising results concerning the possibility to broaden the range of qualified welding procedures. This expectation is based on the good results of diffusible hydrogen, porosity, impact toughness and ductility down to 20 m equivalent water depth. The susceptibility of hydrogen cracking in weld metal and in heat affected zone was estimated comparatively. The presence of hydrogen cracks is discussed as an important limiting factor for the qualification of welding procedures in the class A of the AWS D3.6M:1999 specification.
A Time-Variant Reliability Evaluation Method on Fatigue of Riser System
Authors: Sun Hai , Sun Liping , Dai Wei
Published: January 2011

Riser has been and will be an important part of the offshore production system. Due to the complexity of environment, reliability evaluation is needed for the riser system to ensure the safety and durability. The analysis of the failure modes of riser system was studied in this article, firstly, the main factors of which may lead to failure of riser system were analyzed and classified; secondly, a time-variant reliability evaluation method was proposed to calculate fatigue reliability of riser system; finally, riser fatigue reliability of a certain FPSO is calculated by the proposed method, the results showed that time-variant reliability can better externalize safety of riser during structural service. The proposed method of this paper was significance in safety and integrity assessment of riser system.
Numerical Simulation of Welding Distortion Using Equivalent Thermal Strain Scheme
Authors: Huang Hui , Zhao Yao
Published: January 2011

Welding distortion is one major problem aroused in component assembly, which is typical in marine engineering. Predicting the deformations accurately and reducing the values effectively are very important to maintain good assembly quality and provide useful advice for welding technology. A thermal strain method, based on the inherent strain theory, is developed to precisely predict welding distortion. The paper describes an equivalent thermal strain formulation that derives the height of the layer with orthotropic expansion property and the coefficients of expansion. Welding deformations such as angular distortion and transverse shrinkage can be easily obtained by elastic FEM for welded part. In this study, inherent deformations are calculated with the results of thermal elastic-plastic finite element method, and two typical welding joints are simulated by the new developed method. The deformation results of the proposed method show good agreement with experimental results. Furthermore, welding distortion of a large structure is also simulated by the proposed elastic FEM. Comparison between numerical results and experiment results verifies the effectiveness of the proposed method in simulating large welding parts.
Study on a Stability Judgment System Based on Time Series Analysis
Authors: Terada Daisuke , Kitagawa Genshiro
Published: January 2011

In this study, from the viewpoint of ship safety, a stability judgment system based on Time Series Analysis is proposed in order to protect large amplitude rolling in rough seas. The examination of the system is carried out using model experimental data obtained with a free-running test involving a container ship. In this system, the data is analyzed with a self-organizing state space modeling procedure, and ship motion parameters that characterize the ship motion are identified at every moment. Moreover, a safety index is defined by using the identified parameters, and the stability of the ship is determined. It is confirmed that the proposed system is a powerful tool for determining the stability of the ship. Some future problems with respect to the online identification are also considered.
Dynamic On-Bottom Stability of Shallow Water Pipeline: A Case Study
Authors: Kien Lim Kok , Ming Lau Siew , Badaruddin M. Fauzi B.
Published: January 2011

Traditionally, on-bottom stability requirement of offshore subsea pipelines is often determined based on simplified forcebalance methods. Despite its’ relative ease of application and quick result time, the predicted requirement for stabilisation in shallow water and/or hostile environment can be overbearing and the practicality to install such pipes and subsequent cost becomes a major issue. This paper describes the approach of using dynamic on-bottom stability analysis as pre-requisite to achieve the requirement for stability of subsea pipeline. It was adopted for the determination of concrete coating weight requirements of a 24-inch pipeline in shallow water offshore Sabah, Malaysia, a maiden application of this approach in Malaysian waters. Citing the above as a case study, several key differences in this approach as opposed to traditional methods will be discussed such as the use of a simulated random sea-state in time-domain, advanced pipe-soil interaction modelling, realtime update of hydrodynamic forces and effects of pipeline stiffness on its overall response. The merits of a dynamic stability design approach will also be highlighted in terms of the final stabilisation requirements and its impact on installation and cost.
Low Cost Inertial Measurement Unit Application on Sub-Sea Launching: Signal Processing and Trajectory Algorithm
Authors: Lavieri Rodrigo Sauri , Tannuri Eduardo Aoun , Fujarra Andre´ L. C. , Pesce Celso P. , Correˆa Diego Cascelli
Published: January 2011

Many situations in the Offshore Industry require equipment to be launched to the sea floor, becoming important to measure or to estimate their final position and/or to determine the complete trajectory. Some examples are the installation of anchorage devices, manifolds or production line supports. The main problem associated with the estimation of the position and the trajectory of the equipment is related to the fact that, systems such as GPSs and magnetometers cannot be used in subsea conditions. Gyrocompass and precise inertial sensors can be used, but they are expensive equipments and there is the risk of damaging during the launch process. The solution is to develop cost-effective inertial positioning systems that reach the operational requirements related to measuring accuracy. These equipments are based on MEMS (Micro-Electrical Mechanical Systems) inertial sensors that are relatively cheap. However, without the proper care, the signals obtained by these equipments present large levels of noise, bias and poor repeatability. The aim is to show a sequence of test procedures, treatment and processing of signals that leads one to know the position, attitude and trajectory of a submarine device. Furthermore, it allows the quantification of errors and, eventually, their sources. A commercial IMU (Inertial Measurement Unit) was chosen as a case study. It is equipped with MEMS sensors, usually adopted by the automobile industry. Tests with IMU were carried out intending to find the sensors scale factors, their bias and temperature sensitivity. Thereafter, the data were processed by two distinct algorithms. The first one is a simple algorithm that computes the attitude, azimuth at the final position and calculates the terminal velocity during the launch. The second one integrates the signal along all the movement by using quaternions algebra, resulting in the complete trajectory of the body. Discussions about the accuracy, applicability and limitations of each method are presented.
Study of Soil Responses Adjacent to Jack-Up Spudcan Foundation
Authors: Xie Yi , Leung C. F. , Chow Y. K.
Published: January 2011

Centrifuge model tests have been conducted to investigate the soil responses during penetration, jack-up rig operation and extraction of a jack-up spudcan foundation in soft clay. The penetration and extraction process of a half-cut spudcan were captured by a digital camera at 100g. Image processing technique involving Particle Image Velocimetry was then applied to evaluate the induced soil movements in the adjacent field of the moving spudcan. The development of pore pressures adjacent to the spudcan was also monitored.
Numerical Study of the Effectiveness of a Moving Sloshing Suppression Device
Authors: Tsukamoto Marcio Michiharu , Cheng Liang-Yee , Nishimoto Kazuo
Published: January 2011

In the present paper, a moving device to suppress sloshing is proposed and analyzed. The effectiveness of the suppressing device is evaluated by numerical simulations based on MPS (Moving particle semi-implicit) method. As the parameter of study, lateral forces on the tank walls are used. The results shows that the device reduces remarkably the lateral sloshing forces when filling ratio is low and it eliminates the occurrence of hydrodynamic impact on the tank ceiling when the filling ratio is high.
Experimental Investigation of Invar Edge Effect in Membrane LNG Tanks
Authors: Graczyk Mateusz , Berget Kjetil , Allers Joachim
Published: January 2011

Sloshing, a violent fluid motion in tanks is of current interest for many branches of the industry, among them gas shipping. Although different methods are commonly combined for analyzing sloshing in LNG carriers, time histories of the pressure in the tanks are most reliably obtained by experiments. Very localized pressures may be important for the structural response of the tank containment system. Moreover, the typical pressure time history duration is similar to the structural natural frequency. Therefore, pressure measurements need to be performed with due account for temporal and spatial distribution. This requires a high sampling resolution both in time and space. Fine spatial resolution becomes especially important when local pressure effects are of interest, such as pressure profile passing a membrane corrugation of Mark III containment or Invar edge of No.96 containment. In this paper experimental approach applied by MARIN-TEK for analyzing sloshing phenomenon is presented. The focus is put on investigating effects of Invar edges. A transverse 2D model of a typical LNG carrier is used. Local pressure effects are investigated based on low filling level tests with different wall surfaces: smooth and with horizontal protrusions representing the surface similar to the No.96 containment system.
Visible Space by Landscape Recognition of Local Inhabitant and Its Composition in Japan
Authors: Ohuchi Hirotomo , Yamada Satoshi , Ouchi Setsuko
Published: January 2011

This study discusses relationship between the extent of the sphere of cognition by local inhabitants in coastal fishing area and the physical environment, as ascertained from a questionnaire survey of local inhabitants. Object is 59 coastal fishing villages (Izu and Bousou peninsula in Japan) in which the sea, a town, and a mountain are realized in one, and has complicated geographical feature. We have been researched the complexity and metamorphosis patterns of common areas in coastal fishing regions using sphere graphic method. Based on research, this study analysis Explicate Order and Implicate Order formed from the mutual relationship of the cognitive region and visibility and determine relationship between cognitive attribution and visibility. We analysis visibility with visible region image using the 3-dimensional shade picture which applied the inverse-square damping which is approximation to man’s visual recognition and which is obtained from a spread of light. From above analysis, correlativity of cognitive attribution and visibility by landscape recognition of local inhabitants was shown and its Composition was determined.
Stability of Sand Beds Around Mattress-Curtain Sets
Authors: Xie Liquan , Liu Shuguang
Published: January 2011

We propose a new countermeasure to protect sand beds from erosion, called mattress-curtain sets. Physical model tests in a rectangular flume with suspended sediments were carried out to investigate stability of the sandbed around a mattress-curtain set, and the working mechanism of a mattress-curtain set is discussed. Moreover, based on the experimental results and simulations with software FLUENT, the interactions between sand beds and near bed flow were investigated when a mattress-curtain set was installed on the sand beds. The results show that the stability of sand beds is closely controlled by the seepage under the fabricated mattress, and is affected by liquefaction, excess pore pressure buildups in the sand beds when subjected to changing flow or wave current.