bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Design for Floating Offshore Platforms
Authors: Khonsari S. V. , England G. L. , Moradkhan E. , Valikhani A. R. , Bahadori M. R.
Published: August 2013

While for shallow waters the use of old offshore jackets still seems efficient and justifiable, for deep and ultra-deep waters such platforms cannot be used. During the past few decades the old generation of fixed offshore platforms was succeeded by the new floating platforms and new designs such as FPSOs.

A new family of floating offshore platforms has been developed. These should be able to respond to size, weight and space for operating equipment, i.e. they can be constructed to have a wide range of load-bearing capacities. Use is made of the old concept of Life Saving Tubes, which in their simplest form can be a toroidal shaped tyre inner tube. The Torus-shaped idea can be further extended to other shapes obtained either by revolving any plane closed curve or poly-line about a coplanar axis which does not intersect it, or by extruding the curve/poly-line through a closed path.

The preliminary ‘structural’ calculations carried out on various samples of the torus-shaped members of this family of platforms showed that theoretically they can be designed to carry as much load as required and provide the users with the required space on the water. Moreover, basic studies of the stability of such systems in water showed their large metacentric heights as well as large righting moment arms, hence their high degree of stability. This stability can be further increased by using other versions of this idea with more efficient toroidal shapes. Furthermore, apparently, much study is required however to establish this idea as a viable, cost-effective and efficient alternative for current generations of offshore floating platforms.
Development of a New Underwater Piling Noise Mitigation System: Using Hydro Sound Dampers (HSD)
Authors: Kuhn Christian , Bruns Benedikt , Fischer Jan , Gattermann Jörg , Elmer Karl-Heinz
Published: August 2013

The aim of the recently published climate control by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) is a reduction of the German greenhouse gas emissions down to 20 % in 2050, compared to the generated greenhouse gas in 1990. To reach the given target a huge growth in renewable energy is necessary. One of the most potential possibilities to produce renewable energy in Germany will be the installation of offshore wind turbines.

During the installation of offshore wind foundations such as monopiles, tripods, tripiles and jackets, mostly large tubular steel piles are impact driven to final penetration depth. In the process of impact driving, considerable underwater sound emissions will appear. In recent times, peak sound pressure levels above 190 dB re 1 μPa have been measured at a distance of 750 m away from the installation ground. These peak sound pressure levels, produced during the installation of any kind of driven offshore foundation, is potentially harmful to marine life, in particular to marine mammals such as harbor porpoises, harbor seals or grey seals.

To protect the marine life the German Federal Maritime and Hydrographic Agency (BSH) set the maximum allowed underwater sound pressure level to 160 dB (SEL) at a distance of 750 m away from pile driving.

To reach the given target by the BSH a new underwater piling noise mitigation system using so called hydro sound dampers (HSD) is presently developed at the Institute for Soil Mechanics and Foundation Engineering at the Technische Universität in Braunschweig (IGB-TUBS). After small scale tests in the so called ‘large wave channel’ in Hannover a full scale test was performed in the Baltic-Sea some weeks ago.

The results of the measurements are very promising, as a reduction of 12 up to 20 dB could be generated. Besides existing noise mitigation systems one of the main advantage of the hydro sound dampers is, that the mitigation can be pre-adjusted to a predefined frequency range, as marine mammals are sensitive only for a certain sound frequency range.

In this paper, the results of the small and large scale tests and some new research findings concerning the shape and the material of the hydro sound dampers will be presented.
Optimization Study on Pump Series Setting of Deep-Sea Mining Pipeline
Authors: Yang Kang , Yang Qi
Published: August 2013

Along with the running up of land resources, deep sea exploitation has been important strategic goal of big countries of the world, there are significant meanings to realize efficient and low-energy-consumption piping of deep sea mine. Base on the vertical piping theory of large particles and theory of centrifugal pump, operation points are solved in different working conditions with provided pump series. Consider the problem on the optimization indexes of efficiency, production, power and energy consumption per unit production, conduct analysis and make comparison according to diagrams, optimize the setting of pump series, so as to realize the optimization of pipeline system. The results show that energy consumption per unit production at a higher pump series can be obtained at the minimum, it also ensures higher production and better pump efficiency, this pump series can be selected as the optimal one.
Dynamic Analysis of Offshore Monopile Wind Turbine Including the Effect of Scour
Authors: Li Hui , Ong Muk Chen , Leira Bernt J. , Myrhaug Dag
Published: August 2013

An engineering approach to dynamic analysis of an offshore monopile wind turbine is presented in this paper. The interactions between the foundation and the soil are simulated by nonlinear springs, which stiffnesses are obtained from the axial load transfer (t-z) curve, the tip load-displacement (Q-z) curve and the lateral load-deflection (p-y) curve. Three types of soil conditions are considered in the simulations; 100% sand layer, 50% sand layer (top) and 50% clay layer (bottom), as well as 100% clay layer. Wind, wave and current loads on the wind turbine in operational conditions are taken into account. The variation of the dynamic responses of the wind turbine due to the effect of scour is investigated by comparing the results between the cases with and without scour.
Comparison of Two Six-Degree of Freedom Simulation Models for Mini Autonomous Underwater Vehicle
Authors: Fei Duan , Shuo Pang
Published: August 2013

This paper presents the modified numerical model based on the REMUS simulation model proposed by Timothy Prestero in his paper of MTS/IEEE Conference and Exhibition in 2001 when using it to simulate the “MAUV-III” Mini Autonomous Underwater Vehicle (AUV) of author’s laboratory. In addition, it describes the “MAUV-II” numerical model proposed by Wangbo in his Master thesis of Harbin Engineering University. Because of the inaccuracy of the calculated values of lift and drag coefficients under a series of rudder angles of attack based on the FLUENT software, which is proved by the actual experiment. The calculation method is modified by multiplying by 1.2 as the correction coefficient. After modification, the simulated results are proved to very close match to the experiment data. Based on the corresponding experiments including Circle Maneuver in horizontal plane and diving motion in vertical plane under given operation conditions, these two numerical models are shown to accurately simulate the motion of the “MAUV-III” AUV, especially for the modified REMUS model.
The Salt Flux in the Pearl River Delta, China
Authors: Zhu Yuliang , Wei Xiaoyan , Xu Chencheng
Published: August 2013

The increase of saltwater intrusion in recent years in the Pearl River Delta, has threatened the freshwater supply in the surrounding regions, especially the cities of Zhongshan, Zhuhai, Guangzhou in Guangdong Province and Macau. A numerical modeling system using nested grids was developed to simulate the salinity distribution in the Pearl River delta, and then to investigate the salt transport process and calculate the salt flux for each outlet in the Pearl River estuary. The model forcing functions consist of tidal elevations along the open boundaries and freshwater inflows from the major tributaries in the Pearl River system. The model simulation results are in qualitative agreement with the available field data. The salt flux of the Pearl River delta during the spring tide in dry season is up to 19.5×106ton/ tidal period, while the salt flux during neap tide is only 5.1×106ton/ tidal period, 26.18% of that during the spring tide. The salt flux in Dahu and Guanchong stations are the highest among the stations of the eight outlets, indicating that Humen and Yamen are the most important entries for saltwater intrusion in the Pearl River delta. The most important reason is that the ratio of stream flow to tide flow is different for each outlet. The ratios at Humen and Yamen are the smallest among the eight outlets (<1 for each month), while the ratio at Modaomen is the biggest (>1 for each month), which leads to the lowest salt flux at Modaomen. Salinity distribution in different time periods shows that saltwater intrusion during the spring tide is much more serious than neap tide, and water in many cities during this time period will be unavailable for drinking, irrigation or for ecological purpose.
Optimization of FPSO’s Main Dimensions Using Genetic Algorithm
Authors: Mazerski Grzegorz
Published: August 2013

An efficient concept design of FPSO is supported by a wide variety of tools and methods. Some use parametric solutions for a variety of projects, while others deal with project-specific issues.

One of the early challenges is to establish main dimensions of the “buoyancy element” for Floating Production System. The size should provide appropriate load-carrying capacity at minimum cost within limits of a given field development project. Since the financial implications of the hull size are significant, the choice should be made by means of a proper engineering study. One of the most promising approaches to this task is to utilize Multi Objective Genetic Algorithm (MOGA) for optimization of main particulars.

A method was developed that aims at finding optimum main dimensions of the FPSO unit of given storage capacity with respect to steel weight and strength. This was achieved by utilizing MOGA optimization tool available in NAPA stability software package. The paper presents procedures, challenges and samples of results of such studies. The method was recently utilized in two different FPSO concept projects. First comments and conclusions that were drawn from the results of the procedure will be presented. Some ideas for future development will also be given.
Application of an Absorbing Boundary Condition in a Wave-Structure Interaction Problem
Authors: Duz Bulent , Huijsmans Rene H. M. , Borsboom Mart J. A. , Wellens Peter R. , Veldman Arthur E. P.
Published: August 2013

For the design of offshore structures, an accurate assessment of the ability of the structure to survive in extreme sea conditions is of prime importance. Next to scaled model tests on the structure in waves, also CFD capabilities are at the disposal of the designer. However even with the fastest computers available, it is still a challenge to use CFD in the design stage because of the large computational resources they require.

In this study we focus our attention on the implementation of an absorbing boundary condition (ABC) in a wave-structure interaction problem. Unlike the traditional approach where the boundaries are located far from the object to avoid reflection, we gradually locate them closer while at the same time observing the influence of the absorbing boundary condition on the solution. Numerical calculations are performed using the CFD simulation tool ComFLOW which is a volume-of-fluid (VOF) based Navier-Stokes solver. Comparisons with experimental results are also provided and the performance of the ABC is discussed.
Modelling of Marine Riser Tensioner Load Variations and Implications for Minimum Top Tension Settings in Drilling Risers
Authors: Gallagher Conor , Williams Dara , Lang Donogh
Published: August 2013

As the pace of deepwater oil and gas exploration continues to grow, so too does demand for modern drilling vessels with equipment capable of operating in water depths of 10,000ft or greater. These greater water depths place significant demands on the drilling riser and the riser tensioning system. Modern riser tensioners are complex hydro-pneumatic systems and far from applying a constant top tension, the stiffness and damping characteristics associated with the tensioner mean that the applied tension can vary substantially as the tensioner strokes in response to vessel heave. As a result it is critical that the riser tensioner system response be captured in sufficient detail when evaluating the loads on the drilling riser.

Riser tensioner systems for deepwater drilling must be capable of supplying the required tension to satisfy the minimum stability tension requirement, as per API RP 16Q; however this recommended practice does not adequately account for dynamic tensioner load variation, which can be up to 50% of the nominal tension. For deepwater drilling riser systems, where riser load limits are being approached, accurate modeling of the tensioner system load variation is required to ensure that the riser does not experience compression or excessive stresses. Furthermore, as the dynamic tension variations are largely velocity dependent, they can be relatively independent of water depth. Thus larger percentage variations in tension are experienced at low tensions when compared to higher tensions. This is an important consideration when calculating minimum top tensions for deepwater drilling rigs in shallower water depths.

This paper presents a comparison of the response of a direct-acting riser tensioner (DAT) system for a range of environments. The comparison is based on results from detailed tensioner models that include the individual hydraulic and pneumatic components of the tensioner system and that are fully integrated with a non-linear 3D structural FE analysis tool [1]. The FE model is based on a widely-validated-non-linear software tool [3]. The detailed tensioner model has been validated against manufacturer performance data for existing in-service tensioner systems. The detailed tensioner model has also been used as part of a drilling riser recoil analysis study [1] which provided a good comparison of recoil analysis results against a published recoil test case. The impact on the global riser response of accurately modeling the tensioner system behavior is demonstrated, while the implications for the calculation of minimum top tension are also discussed.
The Influence of Drilling Rig and Riser System Selection on Wellhead Fatigue Loading
Authors: Greene John F. , Williams Dara
Published: August 2013

With drilling and exploration activity currently high in both deep and shallow water regions rig availability and selection is an issue for operators to consider in order to achieve the desired exploration schedule. At present the industry focus is on the development of 6th generation drilling rigs with the capacity to operate in increasing deep water. However despite the focus on deepwater exploration and the associated demand for deepwater drilling rigs there still exists demand for drilling rigs that can operate in shallow to moderate water depths (100m–500m). In addition, certain field development scenarios may exist where planned water depths for drilling activities vary significantly and therefore a drilling rig and riser system is required that can operate satisfactorily in both shallow and deep water depths.

For a given drill site, rig availability or well location, may be such that an operator may have to select a modern deepwater 6th generation rig for shallow water activities where a 3rd generation rig would appear to provide a better solution. Other considerations such as vessel station keeping requirements may lead to selection of a 6th generation rig over a 3rd generation rig, as the former tend to have improved DP thrusters capacity. However it is also important to note that while the 6th generation rigs may have been proven to be robust systems for operation in deep water, the response of a 6th generation drilling system in shallow water depths can be very different to that of an older 3rd generation rig and drilling riser system. Thus careful consideration must be made by the operator when considering the selection of drilling vessels for shallow to moderate water depths. Fatigue life of the wellhead is shown to be affected when one compares the response of the 6th generation and 3rd generation drilling systems in shallow to moderate depths. This also needs to be accounted for when selecting rigs for workover or intervention operations on older infrastructure.

This paper presents a discussion on the various parameters such as BOP stack size, riser, flex joint and vessel design that influence the response of the drilling system in shallow to moderate water depths (100m–500m). A number of case studies and parametric studies have been carried out and the results of these are presented in order to compare the wellhead fatigue damage from the older 3rd generation systems with the 6thgeneration systems and also to identify the critical drivers for this fatigue life reduction.
The Effects of Modelling Techniques and Data Uncertainty in Wellhead Fatigue Life Calculation
Authors: Williams Dara , Greene John
Published: August 2013

Offshore oil and gas exploration continues to move into deeper and more harsh environments and consequently the response of drilling riser systems and associated fatigue loading transmitted to the wellhead and conductor system are of key importance in the design of offshore wells. In addition the presence of ageing infrastructure in mature areas combined with requirements for future workover operations requires careful consideration of both past and future fatigue damage accumulation. In order to estimate remaining fatigue life for the wellhead and conductor the accumulation of damage from each stage of a drilling campaign and phase of operation of a well, including workover and completion operations, must be considered. Thus a detailed global finite element analysis of the impact of riser response, under wave and vortex induced vibration (VIV), on the conductor and wellhead structure is of critical importance.

Traditional engineering evaluation methods to estimate fatigue of wellhead systems in offshore regions with limited availability of environmental data may result in an over estimation of fatigue damage accumulated in the wellhead. Any assumptions regarding fatigue current profiles can also lead to over-prediction of fatigue damage in the wellhead. This can have implications for the planning of future workover operations and may also lead to unnecessary over-design of the system. A further limitation of traditional wellhead fatigue evaluation criteria lies in the assumptions regarding riser tensioner system load response. These methods do not account for the highly nonlinear load response of the tensioner system and can thus significantly underestimate fatigue damage contribution.

This paper presents a more detailed wellhead fatigue analysis methodology to incorporate new analysis techniques, as used for a number of recent applications, to assess with a greater level of refinement the impact of the riser motions on the wellhead fatigue. Specifically this methodology incorporates the generation of a detailed global finite element model of the riser and wellhead system to include detailed non-linear riser tensioner system models, accurate models of the wellhead and conductor, detailed non-linear soil response characteristics and the use of more refined current data as input to VIV calculations.

The details of the riser and wellhead system model are presented and the conservatisms associated with traditional modeling methods with regard to VIV and riser tensioner load variations are discussed. A number of case studies are presented to illustrate the effects of various data assumptions and simplifications on estimated wellhead fatigue.
A Parametric Structure Optimization Method for the Jack-Up Platform
Authors: Yu Yan-yun , Lin Yan , Ji Zhuo-shang
Published: August 2013

In this paper, A parametric structure optimization method, which is called Parametric Structure Shape Optimization Method (PSSOM), is proposed in order to optimize the structure shape of the jack-up platform. According to the characteristic of the jack-up, an approach to create the Parametric Structure Model (PSM) is proposed. The projections of the main structure onto the horizontal plane are used to create the sketch, which is a 2D drawing driven by dimensions. The 3D modeling technique that based on the sketch and feature modeling is used to create the structure model of the jack-up. A meshing procedure is presented to convert PSM into finite element model automatically together with the boundary conditions and the design loads. After calling the FEM solver, the stress and strain for each structure according to any reasonable dimensions could be calculated, and this is the most important foundation of the structure shape optimization design. An optimization design method based on PSM is proposed for the structure optimization design of the jack-up. The genetic algorithm is used to get the optimum dimensions that have better structure strength performance under the premise of that all the other design requirement are satisfied. PSSOM is proved to be practical and high-efficient by the structure optimization of a 300 ft jack-up platform.
Development of Corrosion Resistant Steel for Bottom Plates of Crude Oil Tankers and Onboard Evaluation Results
Authors: Ito Minoru , Kaneko Michio , Nishimura Seiji , Sato Hidehiko
Published: August 2013

Pitting corrosion on the bottom plates of cargo oil tanks (COT) in very large crude carriers (VLCC) is very serious problem. Each tank may suffer up to 1,000 pits, with some reaching a depth of as much as 10 mm. As a result, the workload of repairing such pitting corrosions in periodical dock inspection is extremely heavy. Many studies have already been conducted to clarify the mechanism of pitting corrosion, but it has yet to be fully understood.

We have clarified the pitting corrosion mechanism through onboard research on some VLCCs and various corrosion tests, in addition to the findings obtained by previous studies. Based on our understanding of the mechanism, we developed a corrosion test method to simulate the corrosive environment within the pits. Furthermore, we developed a new corrosion resistant steel (CRS) with trace amounts of alloying elements. The corrosion rate for CRS is less than one-fifth of conventional steels. Due to its very low alloy content, the weldability and mechanical properties of CRS remain similar to conventional steels. This CRS has already been applied to several VLCCs and we have examined its corrosion resistance through onboard investigations of the two VLCCs. One was for all its uncoated COT bottom plates, which were built of CRS, at the first docking (after 2.5 years). No pits deeper than 4 mm were found in the bottom plates of any COTs. Also, only about twenty pits of 2∼4-mm depth were found. The other was for the bottom plates of six unpainted COTs built of CRS at her first and second dockings (after 2.3 and 5 years). At five years, tens of pits deeper than 4 mm were found in all, but the pit count was much lower than that of VLCCs constructed of conventional steel. Thus, the good corrosion resistance of CRS was confirmed. In addition, it was also revealed through onboard research during a dock inspection that pit growth halted on VLCCs with more than five years service.

SOLAS II-1 Cargo Oil Tank Corrosion Protection, which adopts the test method developed by us as the qualification test for bottom plates, comes into effect in 2013. In addition, CRS has already been certified by Class NK as corrosion resistant steel for COT bottom plates.

CRS is set to play its part in the safe navigation of oil tankers. Furthermore, CRS does not require a protective coating of paint, which also benefits the global environment by reducing the use of volatile organic compounds.
Prediction of Fatigue Crack Initiation Life Based on the Extended Cyclic Plasticity Model
Authors: Tsutsumi Seiichiro
Published: August 2013

In order to simulate mechanical fatigue phenomena under macroscopically elastic condition, the plastic stretching within a yield surface has to be described, whilst the plastic strain is induced remarkably as the stress approaches the dominant yielding state. In this study, a phenomenological plasticity model, proposed for the description of the cyclic loading behavior observed for typical carbon steels during the high-cycle fatigue subjected to stresses lower than the yield stress, is applied for the prediction of fatigue initiation life. The model is formulated based on the unconventional plasticity model and is applied for materials obeying isotropic and kinematic hardening law. The mechanical responses under cyclic loading conditions are examined briefly. Finally, the initiation life of fatigue cracking is discussed based on the proposed model with the damage counting parameter.
Numerical Simulations of Regular Waves in a Hydrodynamic Laboratory Basin
Authors: Silva Monica Campos , de Araújo Vitola Marcelo , Pinto Waldir Terra , Levi Carlos Antônio
Published: August 2013

Hydrodynamic behavior of offshore floating structures is of fundamental practical importance to engineers and designers. Physical modelling of offshore structures in hydrodynamic laboratory is a common practice in this field. Due to the increasing in the computer power and the development of the numerical algorithms, the use of the numerical wave tanks (NWT) have become a complementary tool to the model tests. The knowledge of the drawbacks of numerical model is an important issue for engineers and researchers, especially in the models whose governing equations do not have exact solution. This work presents the application of numerical model to simulate the generation and propagation of regular waves in the LabOcean Basin (LabOceano/ COPPE/UFRJ) using the commercial code Ansys-CFX. A cross-section of the offshore basin have been used. Waves have been generated by flap type wavemaker. Period wave in the range from 1.75 to 3.00 seconds have been simulated. For all tests, the analytical wave steepness is smaller than 0.017. Numerical results have been compared with Stokes wave theory and experimental data obtained in the offshore basin. Both the behavior of the free surface and the reflection coefficient have been evaluated. Good agreement was found for the wave profile, mean wave height and mean wave period. Divergences between numerical and experimental results were found evaluating the reflection parameters.
Stochastic Analysis of Impact Loads on Marine Structures
Authors: Helmers Jens B. , Sun Hui , Landet Tormod , Driveklepp Torgrim
Published: August 2013

An efficient Monte Carlo method is developed to perform the stochastic analysis of slamming loads on marine structures. The probability distribution of the maximum impact force during slamming is established for a given stationary sea state. The method is demonstrated by using a uniform wedge and Wagner’s flat plate theory. Stochastic effects related to deadrise angle, flow separation from the knuckle, vertical position of the structure, vertical motion and roll motion are investigated. The statistics of other parameters such as the duration of the slamming event and the maximum penetration of the structure into water are also assessed.
Nonlinear Response of Coupled Integrated Spar Platform Under Severe Sea States
Authors: Islam A. B. M. Saiful , Jameel Mohammed , Ahmad Suhail , Jumaat Mohd Zamin
Published: August 2013

The oil and gas industry has moved towards the offshore deep water regions due to depletion of these resources in shallow and intermediate water depths. Conventional fixed jacket type platforms and bottom supported compliant platforms have been found to be inefficient and uneconomical for exploring these resources in deep water regions. In view of deep water conditions, Spar platforms have been seen to be the most economical and suitable alternative offshore platforms. Several operational Spar platforms such as SB-1, Shell’s ESSCO, Brent Spar, Oryx Neptune Spar, Chevron Genesis Spar and Exxon’s Diana Spar in the Gulf of Mexico and North Sea have shown the effectiveness and success of such platforms in deep-ocean. In deep water conditions, the severity of sea states has substantial effects on the spar platform. The mooring lines contribute significant inertia and damping because of their longer lengths, larger sizes, and heavier weights. Precise motion investigation of platforms should consider these actions in deep waters. However, proper dynamics cannot be assessed by the commonly used decoupled quasi-static method that ignores all or part of the interaction effects between the mooring lines and platform. Coupled analysis, which includes the platform and mooring lines in a single model, is the only way to capture the damping from mooring lines in a consistent manner. In the present study, coupled analysis of integrated Spar-mooring system has been performed. Cylindrical spar hull is treated as a rigid beam element and catenary mooring line as hybrid beam element. Nonlinear dynamic responses have been evaluated under several severe sea states of dissimilar wave heights and wave periods. Damping due to mooring lines has been assessed. An automatic Newmark-β time incremental approach has been implemented to conduct the analysis in time domain. Wave induced spar hull motion in surge, heave and pitch direction along with maximum tension in mooring line has been assessed for different wave conditions with and without current in 1018 m water depth. The time histories of spar responses follow substantial alteration for larger wave heights and wave periods. Maximum tensions in mooring line are very sensitive with momentous value for extreme sea loading. Mooring tension responses are significantly different reflecting the damping effect of mooring lines.
A Validation of Various Codes Using Hydrodynamic Wedge Impact Data
Authors: Jiang Minyee , Lien Van , Lesar Douglas , Engle Allen , Lewis Richard
Published: August 2013

It is well known that slamming and whipping can significantly contribute to a ship’s structural loading which can severely impact a ship’s operational safety. Therefore, a method of predicting severe transient structural loads is needed, especially for the design of future high-speed patrol boats and high-speed ferries. A number of computational fluid dynamics (CFD) codes have demonstrated the ability to cope with complex body shapes and to numerically capture the nonlinear effect of hydro-elasticity. However, validation is scarce both due to a lack of experimental data and the computational intensity of the problem.

This paper describes a validation study of a Reynolds averaged Navier-Stokes (RANS) code (STAR-CCM+) and a Lagrangian-Eulerian fluid structure interaction (FSI) code (DYSMAS) using 10 degree wedge drop test experimental data obtained at the Naval Warfare Center, Carderock Division, December 2010.
Interaction Between Offshore Pipelines and Migrating Sand Waves
Authors: Matthieu Jordan , Raaijmakers Tim
Published: August 2013

Large areas of shallow, sandy seas are covered by migrating tidal sand waves. Sand wave migration rates are on the order of 10s of meters per year, with heights between 10 and 30% of the water depth. If such regions are traversed by pipelines, the dynamic interaction between the rock-berm protection of the pipelines and the migratory sand waves must be accounted for to assure the long term stability of both the rock-berms and pipelines. This study employs a 2DV model to demonstrate the hydrodynamic and morphodynamic interaction between migrating sand waves and a rock-berm constructed perpendicular to the migration direction. The timescale of sand waves and the design life of rock-berm are similar, consequently, rock-berms in sand wave regions experience a change in bed level approximately equal to that sand wave height. Due to the large difference in temporal scales between local erosive processes and sand wave migration, the passing of a sand wave is manifest as a general rising or falling of the ambient seabed, while a rock-berm is fixed at its construction elevation. Consequently, the critical design case is for a rock-berm constructed at a sand wave crest since the surrounding bed level decreases throughout the operational life of the pipeline. A conservative design approach is to construct rock berm protection in a sand wave trough, resulting in rising ambient seabed levels throughout the operational lifetime of the underlying pipeline or electrical cable.
Strength and Reliability of Ships ‘As-Built’
Authors: Žiha Kalman , Kodvanj Janoš , Ljubenkov Boris , Dupor Nikola , Bakić Ante
Published: August 2013

This report firstly presents the rule based scantlings and sectional properties of the example ship defined by using the nominal properties of mild shipbuilding steel. It also describes the way of collection of characteristic material specimens of rolled steel plates and bars delivered by the steel manufacturer to the shipyard for to the example ship.

Secondly it summarizes the results of tensile testing in the Laboratory for experimental mechanics of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb of plates and bars denoted here as ‘in-built’ material properties for the example ship according to the production plans.

The report then reminds on the rule based material properties for acceptance purposes. Next it considers the influence of ‘in-built’ mechanical properties with respect to the rule requirements on local, global and ultimate strength of ships. The report discusses material properties other than yield strength, which participate in the assessment of the overall ship safety such as the weld strength, buckling and fatigue strength, low temperature behavior, corrosion and reliability.

The results of the tensile testing of ‘in-built’ materials are then applied to checking of the local, global and ultimate ‘as-built’ strength of the example ship’s hull instead of the ‘as-designed’ strength defined by the nominal material properties.

The report at the end discusses the differences between the ‘as-designed’ and the ‘as-built’ hull strength, fatigue life and reliability. It suggests minimization of the hull strength uncertainties by adopting the mechanical properties of ‘inbuilt’ materials. The conclusion supports the stirring idea of this report that in addition to the ‘as-designed’ strength, a ship deserves individualized assessment of the “as-built” ship hull strength based on the measured realistic ‘in-built’ properties.
Risk Mitigation Through the Application of New Power Umbilical Technology
Authors: Dobson Alan , Frazer Steven
Published: August 2013

This paper describes the substantial service life improvements that can be achieved through a new, high technology solution developed for deep water electrical power umbilical and cable applications. The new design represents an enabling technology for power cable projects in the deepest and most dynamic waters, provides a lower risk solution for risers in highly stressed conditions and can give a technically improved solution for the range of electrical power umbilical application.

The significant advantages of aluminum alloy cable bundles over traditional copper cable bundles under static and dynamic loading associated with a typical deep water floating installation are presented. A design case study is used to illustrate improvements in structural response and fatigue life associated with the aluminum alloy cable cores against conventional technologies. The paper concludes with an overview of the associated risk reduction through the implementation of the aluminum alloy cables in the form of a failure mode and effect analysis.
Rod Dynamics With Large Stretch
Authors: Webster William C. , Lambrakos Kostas , Kim Jangwhan , Jing Xiaoning
Published: August 2013

In the last few decades, the use of synthetic fiber line in mooring systems has become increasingly popular, for instance in composite moors consisting of wire rope, polyester line and chain. Synthetic fiber lines are noted for their large stretch which can under high load be as much as 10 to 20 percent of their unloaded length or more. In developing a consistent model for the motions of a moored offshore platform using composite moors, it is necessary to model the dynamics of the moor recognizing that some elements may exhibit large stretch. The model for the dynamics of a rod without stretch was developed by Garrett (1982). This model has been frequently extended to the case with small stretch by linearizing the stretch term in the compatibility equation, for instance, Paulling & Webster (1986). The research presented here is an extension of Garrett’s theory to include the possibility of large stretch. With the adoption of a simple assumption concerning the character of the stretch, and with the incorporation of visco-elastic behavior of the large-stretch elements given by Kim, Kyoung & Sablok (2010), large stretch can be introduced consistently with few changes in the traditional finite-element scheme. Finally, the effects of large stretch on the physical properties and dynamics of the rod are also discussed.
Full Scale Sour Fatigue Testing With Dense Phase Gases
Authors: Vargas Pedro M. , Crowder Ben , Yu Weiwei , Mishael Sam , Armstrong Keith
Published: August 2013

The petrochemical industry is very interested in the sour service fatigue performance of girth welded steel pipes. As a result several papers are published every year addressing this issue, and several Joint Industry Projects (JIP) are currently underway addressing different aspects of sour service performance of steel pipelines. To date research work has focused on quantifying the fatigue performance via small scale specimens due to the difficult and danger in dealing with H2S. Currently a JIP is underway that promises to provide full scale fatigue performance of pipeline welds under sour service.

This paper documents the knockdown-factor-on-life (KD) determination for full scale sour service testing. In an industry first, a very difficult full scale sour service test was performed: 1) High Pressure, 2) High content of H2S, 3) Dense phase gases with ultra low water content (less than 400 ppm), and 4) Loading rate of 0.01 Hz. The loading was applied in full longitudinal tension. The full scale sour tests are compared with full scale in-air tests to obtain the knockdown factor. Resource constraint limited the number of full scale tests to 3.

The main objective of the tests for the practical application was to ensure that the usage of crack growth based knock-down factors, i.e. the use of Fatigue-Crack-Growth-Acceleration-Factor (FCGAR) from small scale fracture mechanics specimens, was reasonable and conservative.

Some additional comparisons are done with crack-growth based knockdown factors that may help explain the effect of the ultra-low water concentration. Knockdown factors from small scale crack growth specimens, Fatigue-Crack-Growth-Acceleration-Factor = 60 (FCGAR), are significantly higher than the full scale results, KD = 7. The ultra-low-water dense phase gases do not pit the surface, thus leaving the initiation life relatively intact. The knockdown factor for the full scale test is then mostly the result of the accelerated crack growth that occurs once a macro-crack nucleates.
Analysis of the Physics of Bilge Keel Vortex Generation
Authors: Minnick Lisa , Bassler Christopher , Percival Scott
Published: August 2013

A 2D forced roll oscillation experiment was performed to examine and characterize the physics of vortex generation from ship bilge keels. Measurements included ship model motions, normal force on the bilge keels, and flow field visualizations using Particle Image Velocimetry (PIV). Data was collected for a range of roll oscillation amplitudes, including large amplitudes where the bilge keels interacted with the free surface and for three roll oscillation frequencies.

This paper presents analysis and description of the observed phenomena, and examines whether a functional relationship can be established between the force measured on the bilge keel and the flow field generated by the bilge keel. A qualitative discussion of the observed flow characteristics, including the vortex generation at the tip of the bilge keel, detachment, and interaction with the free-surface, is presented. In addition, the circulation in front and behind the bilge keel was calculated, analyzed, and compared to the measured bilge keel force. The analysis conducted was intended to provide improved understanding of the phenomena which occur during bilge keel vortex generation and aid in the development of improved roll damping and bilge keel force models for the prediction of ship motions.
Fatigue Life Analysis for a Steel Catenary Riser in Ultra-Deep Waters
Authors: Rodrigues Marcos V. , Ferraz Caroline , da Silva Danilo Machado L. , Nabuco Bruna
Published: August 2013

With new discoveries in the Brazilian Pre-Salt area, the oil industry is facing huge challenges for exploration in ultra-deep waters. The riser system, to be used for the oil transportation from seabed to the production unit, is one of them. The definition of riser configurations for ultra-deep waters is a real challenge. Problems have being identified for flexible risers, hybrid risers and steel catenary risers (SCR) configurations to comply with rules requirements and criteria in water depths of 2000m.

The objective of this work is to present a study on the fatigue behavior of a Steel Catenary Riser in 1800m of water depth. One of the main challenges for SCRs in ultra-deep waters is the fatigue, due to platform 1st order motions, at the touch down zone (TDZ).

A case study is presented for a Steel Catenary Riser connected to a semi-submersible platform. The influence of some design and analysis parameters is studied in order to evaluate their impact on the SCR fatigue life. The main parameters to be evaluated in this work are: The mesh refinement, in the global analysis, at the Touch Down Zone; The internal fluid density variation along the riser, and; The 1st order platform motions applied to the top of riser; In addition to the results of this paper, some highlights are presented for SCR analysis in similar conditions.
Microstructure and Mechanical Properties of API 5CT L80 Casing Grade Steel Quenched From Different Temperatures
Authors: Palanisamy Vinothkumar , Solberg Jan Ketil , Salberg Bjarne , Moe Per Thomas
Published: August 2013

The continuous development of line pipe and casing grade steels should be complemented by development of more effective welding methods. A special high temperature high speed forge welding technique called Shielded Active Gas Forge Welding (SAG-FW) has been developed to weld steel pipes for a range of applications. This article focuses on the microstructure development at different welding conditions in L80 steel with 0.25%C. Specimens with dimensions 100 mm × 11 mm × 6 mm were extracted from the wall of a large diameter L80 pipe. A SMITWELD thermal simulator was used to simulate heat treatment conditions using electrical resistance heating. The specimens were heated to peak temperatures ranging from 600°C to 1350°C within 10 s and subsequently quenched to 50°C at a constant rate of 60°C/s to simulate the heat-affected zone conditions for the real SAG-FW process. Martensite with small fractions of bainite was observed for higher peak temperatures. Mixed microstructures were observed in the specimens heated in the intercritical temperature range. Microstructures and phase fractions developed after heating to different peak temperatures have been analyzed by optical microscopy and scanning electron microscopy. Charpy V-notch tests and Vickers microhardness measurements have been carried out for the weld simulated specimens. The observed toughness values, hardness values, microstructures and phase fractions have been correlated to the respective weld simulation parameters.
Drill String Strength Evaluation for Deep Earthquake Zone Drilling
Authors: Inoue Tomoya , Kyo Masanori , Sakura Koji , Fukui Toshihiko
Published: August 2013

The scientific drilling vessel Chikyu was designed to have the deep drilling capability to reach the deep earthquake zone. To realize such deep drilling, a drill pipe with higher than ever strength and reliability is of necessity. A strength evaluation of such high strength drill pipe is also necessary.

Around Japan, the earthquake zones are widely located under the seabed in deep water. For example, the Nankai Trough located beneath the ocean off the southwest coast of Japan is one of the most active earthquake zones where large-scale earthquakes have occurred repeatedly throughout history. Thus, the Chikyu has started the first scientific drilling at the Nankai Trough as the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE). NanTroSEIZE targets the megasplay fault zone at 3500 m below the seafloor and finally 6000m deep drilling into the seismogenic zone and across the plate interface into the subducting crust at water depths of around 2500m. In addition, a huge earthquake zone is expected to be located about 1000m below the seafloor at water depths of around 7000m. For this drilling task, the riserless drilling technique should be applied.

To realize such deep drilling with both riser and riserless techniques, a S150 drill pipe was developed during the construction phase and has been used in the past scientific drillings of the Chikyu. For deeper drillings in the future and drilling operations in harsh environments, we are developing superior high strength drill pipes, S155 and S160, possessing high reliability including corrosion resistance to achieve high toughness and reduction of stress concentration. An evaluation of the maximum possible stress was conducted. In the maximum strength evaluation, we considered dynamic stress and bending stress due to the current and the vessel inclination.

This paper describes the development of superior high strength drill pipes and the strength evaluation of such drill pipes for deep earthquake zone drilling.
Experimental and Numerical Plastic Response and Failure of Laterally Impacted Rectangular Plates
Authors: Liu Bin , Villavicencio Richard , Soares C. Guedes
Published: August 2013

Experimental and numerical results of drop weight impact test are presented, on the plastic behaviour and fracture of rectangular plates stuck laterally by a mass with a hemispherical indenter. Six specimens were tested in order to study the influence of the impact velocity and the diameter of the indenter. The impact scenarios could represent abnormal actions on marine structures, such as ship collision and grounding or dropped objects on deck structures. The tests are conducted on a fully instrumented impact tester machine. The obtained force-displacement response is compared with numerical simulations, performed by the LS-DYNA finite element solver. The simulations aim at proposing techniques for defining the material and restraints on finite element models which analyze the crashworthiness of marine structures. The mesh size and the critical failure strain are predicted by numerical simulations of the tensile tests used to obtain the mechanical properties of the material. The experimental boundary conditions are modelled in order to represent the reacting forces developed during the impact. The results show that the critical impact energy until failure is strongly sensitive to the diameter of the striker. The shape of the failure modes is well predicted by the finite element models when a relatively fine mesh is used. Comments on the process of initiation and propagation of fracture are presented.