bluuebunny/crossref_metadata_2025 huggingface dataset:
Wave-in-Deck Impact Load Measurements on a Fixed Platform Deck
Authors: Scharnke Jule , Vestbøstad Tone , de Wilde Jaap , Haver Sverre
Published: September 2014

New methods for estimation of extreme wave crest heights have resulted in an increase of the estimated 10,000 year crest height. At the Norwegian Continental Shelf this increase is typically 2 to 4 m, resulting in a crest height of 22 m to 24 m in the Central & Northern North Sea and the Haltenbanken area. As a result several fixed platforms designed prior to 2000 may experience negative air gap if being hit by the 10,000 year wave crest height. Numerical methods have been used for assessing wave-in-deck impact loads. The model tests discussed in this paper were conducted to be used as verification of the numerical codes.

For the model tests two sea states along the 10,000 year contour line were considered. Several 3-hour (full scale time) realizations were calibrated in order to capture the natural variability of the most extreme crest heights.

For wave deck impact problems, one is merely interested in the few very large wave crests out of a 3-hour simulation. A more efficient test scope would, therefore, be to generate only the largest wave groups of the realizations. For this reason the most extreme crest(s) per sea state were identified and most wave-in-deck tests were conducted by generating only the part of the time series containing the large crest(s). The wave calibration results were discussed in a previous paper, see [1].

For the wave-in-deck model tests, an existing North Sea jacket was built at scale 1:60 and instrumented in order to measure the global loads on the platform deck independently from the loads on the jacket itself. In this paper the model test setup as well as the measured wave-in-deck impact loads are discussed and compared to a simplified load prediction model. The presented results show that the simplified loading model, with wave properties based on Stokes 5th order wave theory, underestimates the measured horizontal deck loads.
On the Scalability of Model-Scale Ice Experiments
Authors: von Bock Und Polach Rudiger U. Franz , Ehlers Sören
Published: September 2014

Ice model-scale tests are a frequently used mean to assess and predict the performance of ships and structures in ice. However, ice model-scale tests may not be treated as a black-box where any full-scale scenario can be tested and a Froude-scalable result is obtained. Prior to scaling a thorough analysis of the physical processes is required and whether they can be transferred to full-scale. Model-scale ice is an empirically developed compound-material, consisting of frozen water, voids of air and other artificial dopants. The model ice manufacturing process and dopant amounts have been adjusted to achieve Froude-scalability for the ice thickness and certain force response levels, i.e. ice resistance tests of ships breaking ice in the bending mode.

However, not much is known about the internal mechanical processes of model-scale ice and how the scaled force levels are reached. This may add uncertainty to ice model tests and their application on new fields. Recent research indicated that the internal mechanics of model-scale ice and natural sea ice are different, which is also challenging some of the existing scaling approaches.

Mechanical specimen tests in full-scale and model-scale are usually compared by stresses, i.e. relating the failure load to the cross-sectional properties. However, depending on the tests different stress combinations might lead to failure, such as different geometries and dimensions may cause qualitatively different stress distribution, which ultimately limits the comparability of the tests.

Subsequently, this paper presents a qualitative assessment on selected topics to assess the differences of model-scale ice and natural ice and the influence of the specimen geometry. Furthermore, existing scaling approaches are discussed in context with recent research findings.
How We Determine the Design Environmental Conditions and How They Impact the Structural Reliabilities?
Authors: Li Linbin , Li Ping , Liu Yuan
Published: September 2014

This paper is based on the JIP study for the oceanographic hindcast and environmental load statistics of fixed steel structures at South China Sea under tropical cyclone conditions. It focuses on the sensitivity and comparison studies by exploring the degrees and reasons of variability that may occur in determination of design environmental conditions resulting from the selection of the design standards and approaches. The bias and efficiency in extreme values prediction are examined with respect to modeling uncertainty and statistical uncertainty. The long term distributions of maximum wave height as well as the associated wave period conditional on the design wave height are derived following the storm event based method. The approaches for combing wave, current and wind to define the design conditions and the associated biases on design load are investigated. Second order random and spreading wave theory is adopted to estimate the extreme wave crest height distributions. The extreme water level issue is addressed and recommendations are given for setting the deck elevation to achieve the explicit wave-in-deck probabilities.

The studies are carried out by applying a dataset of a grid point containing 182 typhoons spanning 40 continuous years to demonstrate the analytical procedures in an understandable fashion. The results of this paper should lead to improvements in prediction of the environmental conditions for design of new-built structures to attain their target safety levels, as well as for assessment of existing structures to demonstrate their fitness-for-purpose.
Heat and Mass Transfer Mechanism of Gas Hydrate Development for South China Sea
Authors: Yu Xichong , Gang Li , Pang Weixin , Yaling Wu
Published: September 2014

The decomposition process of gas hydrate in sediments is actually the dynamic phase transition process of solid hydrate in sediments after absorbing heat decomposition. According to the phase equilibrium characteristics of gas hydrate, there are three basic development methods, including heating, chemical injecting and depressurization. Currently, there is no good commercial software used to simulate heat transmission and mass transfer in the gas hydrate decomposition process. So in this paper, based on typical gas hydrate sediment in South China Sea, microcosmic, mesocosmic (fractal theory) and macrocosmic scales are respectively used to successfully reveal the heat and mass transfer mechanism of three basis development methods. Molecular dynamics simulation shows heat injection is the best method for heat and mass transferring, and chemical injecting is better than depressurization. Fractal theory is successfully used to describe the complex structure of the porous sediments with gas hydrate occurrence, and can realize the prediction of heat and mass transfer law of hydrate dissociation in porous media. Macrocosmic numerical simulation of depressurization for gas hydrate sediment in South China Sea shows gas hydrate reservoir geological model has a large influence on the gas hydrate decomposition, and permeability and hydrate saturation of the upper cover layer have great effect on gas hydrate decomposition. It is poor development efficiency for only depressurization development and the problem of water drainage should be paid attention during development process.
Optimization Method for Oscillation Characteristics of a Spar-Buoy
Authors: Iseki Toshio
Published: September 2014

Numerical studies are carried out to investigate the effectiveness of an optimizing method of oscillation characteristics. The main objective of this study is utilization of the auto-parametrically excited oscillation of single degree of freedom. The subject is limited to the motion of a spar-buoy type point absorber. The device consists of an inner cylinder and 12 outer cylinders. Buoyancy of the outer cylinders is controlled by axial-sliding valves in order to change the heaving period. Model tests were also conducted to investigate the basic characteristics. Based on the numerical simulations in time domain, the possibility of utilization of auto-parametrically excited oscillation for WEC is shown.
The Ocean Observing System for Santos Basin: Project Blue
Authors: de Freitas Assad Luiz Paulo , Fragoso Mauricio da Rocha , Landau Luiz , Adissi Flavia
Published: September 2014

The Santos Basin region is located in the southeast part of Brazilian offshore region and contains the most important presalt oil reservoirs. The oceanographic knowledge of this region is very important for the future challenges related with oil exploration and production. The Ocean Observing System for Santos Basin also known as Blue Project started in August 2012 and its main goal is the development of a pioneer ocean observing system for Santos Basin region (Brazil) based on ocean modeling applications and real time systematic ocean data collection [1]. The data collection program makes use of satellite remote sensing and in situ sensors such as surface drifters, floaters and gliders. The proposed methodology is based in three main research work branches: ocean and atmosphere modeling, real time ocean data collection and disclosure of all the generated information. In this work it will be presented the description of the applied methodology and the preliminary results achieved by the Project.
The State of Dry-Tree Semi-Submersible Platforms for Deepwater Gulf of Mexico
Authors: Lee Ming-Yao , Zeng Jack , Poll Philip
Published: September 2014

The use of semi-submersible platforms has become increasingly popular due to its ability to carry large topsides and the possibility for quayside integration. With recent exploration successes in ultra-deepwater fields of the Gulf of Mexico, major oil and engineering companies are keen to look for a safe, reliable and cost-effective dry-tree option to maximize the value of deepwater field developments. Dry-tree semi-submersible (DTS) emerges as such an option to overcome the water depth and size limits imposed by TLP and Spar, respectively, and enables the platform to carry a large well array and payloads in ultra-deep water. This paper presents the offshore industry’s multi-year efforts to mature two promising semi-submersible platform concepts that can accommodate long-stroke dry-tree risers and have large drilling and production capabilities. Results of technology development and qualification will be highlighted with details on hull performance and hull/riser interfaces. Key structural, mooring and riser analyses and scaled model test results including the long-stroke riser tensioning system will be presented. Remaining challenges that need to be overcome to advance the DTS concepts from “technology acceptance” to “project readiness” will also be discussed.
Numerical Hydrodynamic and Structural Analysis of a Floating OWC at Three Irish Sites
Authors: O’ Sullivan Keith , Murphy Jimmy
Published: September 2014

This paper outlines the process by which a wave energy converter (WEC) is matched to its deployment site, both in terms of power production and structural design. These aspects of device design are critical for the economic feasibility of a wave energy project. The WEC analysed was the backward bent duct buoy (BBDB), a type of floating oscillating water column (OWC) device, while three sites around the Irish coast were considered. Each site has different annual wave conditions, and as such implies different design parameters for both power production and structural design. Using the energy period for each site, the hull shape for the BBDB was determined. Frequency domain modelling was employed to determine the motion and hydrodynamic pressure response amplitude operators (RAO) of each device. The method of superposition was used to determine the power matrix of each device and using wave conditions with a 50 year return period for each site, the maximum loads imposed on the hull were used as the steel design criteria, while the displacement excursions and the typical catenary mooring equations were used to assess the mooring loads and chain design. Representative scatter diagrams for each site were used to assess the annual average power production. The results of the study are presented in terms of annual energy production per tonne of hull steel mass and per tonne of mooring chain mass. These outputs act as indicators for developers to continue, with the optimum site and hull design, into a detailed project economic feasibility assessment.
Investigation on the Post-Ultimate Strength Behaviour of Sandwich Plate
Authors: Wang Wei , Xu Weijun , Yao Xiongliang , Yang Nana
Published: September 2014

This paper focuses on the post-ultimate strength behavior of sandwich plates. With widely application of the laminate on the ship and offshore structures, the post-ultimate strength behavior is becoming more important for safety evaluation of structures. Since the post-ultimate strength behavior can reflect the collapse extent of sandwich plate when subjected to extreme loads. A sandwich plate was modeled by FEM, its load-displacement relationship was obtained and its collapse characteristics were analyzed. The load-displacement relationship indicates its post-ultimate strength behavior, which is shown as that the load carrying capacity has a rapidly reduction when the ultimate strength is exceeded, and that the failure modes of the sandwich plate are determined by the parameter of individual layer. The simulation results were validated against experimental results. Conclusions are drawn: the displacement of sandwich plate under axial compression increased slowly before reaching the ultimate strength, once the ultimate strength was exceeded, the loads exerted on the structures sharply decreased with slowly increased displacement until the plate cracked. The simulation results have a good agreement with the experimental results. The mainly failure modes of sandwich plates can be interpreted as delamination between skin & core and core compression fracture, which are typical failure modes in engineering. The stiffness of sandwich structures decreased due to the interlaminar cracking or skin fracture, further the load carrying capacity decreased, which is of significance for guiding the design of sandwich structures.
Exceptional Fatigue Performances for Umbilical’s Super Duplex Seam Welded Tube Solutions
Authors: Wagner Olivier , Thevenet Gilles , Peultier Jérôme , Roques Jean-Philippe , Romazzotti Henri
Published: September 2014

Since the last five years, an innovative technology for umbilical’s seam welded super duplex stainless steel tubes (grade 2507, UNS S32750) has been developed in order to meet new technical challenges. An extensive program of qualification, based on 4 dimensions covering the full manufacturing range, i.e. internal diameter and wall thickness, has been set. More than 11000 test results demonstrated the efficiency and the stability of the manufacturing process. The results were also confirming the expected properties of the tubes, in term of mechanical characteristics, corrosion resistance and manufacturing tolerances. At the end of this qualification phase, a Type Approval Certificate was delivered by an independent and official certifying authority demonstrating then, the suitability of the product for offshore static applications.

The next step was to confirm the fatigue performance of the product to meet the requirements of umbilicals for dynamic applications.

This paper describes how a dedicated fatigue test protocol has been jointly defined between a Major O&G player and the tube supplier. This protocol has been built in order to test the 3 dimensions already produced during the first step of the qualification, considering tube samples with and without orbital weld. Fatigue test programs are known to be very sensitive to the test parameters, i.e. temperature, test frequency and dimensional properties of the samples. As a consequence, special attention is paid to the description of the testing methodology, the selection of the acceptance criteria and the definition of the testing parameters. Finally, the results of this program are presented and discussed in order to assess the capability of the product with respect to the defined acceptance criteria.
A New Tool for Prioritising the Risk of Failure Modes for Marine Machinery Systems
Authors: Emovon Ikuobase , Norman Rosemary A. , Murphy Alan J.
Published: September 2014

Failure Mode Effect and Analysis (FMEA) is one of the most powerful techniques for performing risk analysis for marine machinery systems, with risk being quantified through evaluating Risk Priority Numbers (RPNs) for all failure modes of the systems. The RPN is traditionally evaluated as the product of three risk criteria; occurrence (O), severity (S) and Detection (D). FMEA has several limitations such as the challenge of aggregating experts’ risk criteria rating that may be imprecise or incomplete.

In this paper some of the limitations in the conventional FMEA technique are addressed using two approaches; AVeraging technique integrated with conventional Risk Priority Number (AVRPN) and AVeraging technique integrated with TOPSIS (AVTOPSIS). Both proposed techniques use a novel approach simple average in aggregating imprecise experts’ risk criteria ratings. A case study illustrates the suitability of both techniques for use in risk prioritisation jointly or independently as the results generated by both techniques are very similar. Furthermore, the AVRPN technique has been applied to an example from the literature and it has been demonstrated to be both computationally simple and capable of producing results which almost completely match those generated by modified Dempster-Shafer evidence theory techniques.
Vibration Analysis of Thick Plates: Analytical and Numerical Approaches
Authors: Senjanović Ivo , Vladimir Nikola , Cho Dae-Seung , Choi Tae-Muk
Published: September 2014

In this paper an examination of methods for vibration analysis of moderately thick rectangular plates has been presented. First, the state-of-the art in thick plate vibration theories and analysis methods is described and it is followed with basic equations of the original Mindlin theory, which represents a starting point for the development of all other mathematical models. Then, the problem of analytical solving of equilibrium equations is considered based on the modified Mindlin theory of thick plate vibrations, which has been published in the literature recently. Further, energy methods that can be applied to arbitrary boundary conditions are discussed and outline of the assumed mode method is presented. Finally, in the context of numerical methods a new quadrilateral finite element, based on the above mentioned advanced thick plate theory, is included. It should be emphasized that it doesn’t suffers of shear locking problem associated with finite elements, due to natural relation among bending and shear polynomials, and moreover, it gives very accurate results. Application of the presented methods is illustrated by several numerical examples which include natural vibration analyses of rectangular plates with various thicknesses and different combinations of boundary conditions (simply supported, clamped, free and elastically restrained). Comparisons of natural frequencies and mode shapes with results available in the relevant literature and with those obtained by the commercial finite element software are also provided.
A Comparison Among Alternatives to Assess FPSO Roll Damping via Model Testing
Authors: de Oliveira Allan C. , Fernandes Antonio Carlos , Soares Anderson R. W.
Published: September 2014

The prediction of the nonlinear rolling motions of a FPSO with extended bilge keels stills a challenging problem. Despite recent advantages in CFD computations, the use of model testing is considered the standard strategy for roll damping assessments. There are different ways to assess the roll damping via model testing and the three most common are the use of decay tests, tests in regular and irregular waves. The comparison among those different kinds of tests may present incoherent results, sometimes, introducing the question of which methodology is the most appropriated in those scenarios, with impact in model test specifications.

Decay tests are the easiest and the most economical way for roll assessments, but they are usually considered inaccurate compared to the other test types. Recent researches, however, have shown that a statistic approach which utilizes several decay data from the same model and loading condition improves the damping predictions. This paper provides comparisons of damping predictions from different test types based in extensive model test campaigns. It also addresses the issues and the lessons learned during the campaigns to obtain the FPSO damping database.
Nanoparticles as Fluid Loss Control Additives for Hydraulic Fracturing of Tight and Ultra-Tight Hydrocarbon-Bearing Formations
Authors: Barati Reza
Published: September 2014

Injection of polymeric solutions, either as slick water or cross-linked fluids, in order to propagate a fracture and distribute proppants and keep the fracture open is a common practice in hydraulic fracturing of unconventional tight and ultra-tight formations. In addition to propagation of a main fracture, polymeric fluids will be invading the already existing network of micro-fractures and extending the network connected to the main fracture. Fluid loss into the matrix rock and micro-fractures is inevitable, so is the use of a comparable fluid loss additive to reduce the filtrate volume.

Different classes of nanoparticles have been used by several researchers to carry different agents including surfactants and enzymes for hydraulic fracturing purposes. Nano-sized pores and micro-sized fractures in tight and ultra-tight formations require a nano to micro-sized fluid loss additive to improve propagation of the hydraulic fractures by efficiently reducing the fluid loss.

In this study, application of silica and polyelectrolyte complex (PEC) nanoparticles as fluid loss additives for three sets of core plugs with permeability values within the 10−5 −10−4 mD, 0.01–0.1 mD and 1–40 mD range was investigated. The nano-sized material used in this study significantly reduced the fluid loss volume for the cores with permeability values below 0.1 mD when mixed only with 2% KCl or with low concentrations of guar polymer prepared in 2% KCl.

Combination of the fluid loss additive application with chemical carrying application makes these nanoparticle systems a suitable package for hydraulic fracturing of tight and ultra-tight formations.
ShallowFlow: A Program to Model Ship Hydrodynamics in Shallow Water
Authors: Gourlay Tim P.
Published: September 2014

In this article we present details of “ShallowFlow”, a computer program to model the hydrodynamic flow around ships in calm shallow water. The program is based on slender-body shallow-water theory. Outputs from the program include far-field hydrodynamic pressure and flow velocities; free surface drawdown; sinkage and trim. Varying transverse bathymetry including open water, dredged channels, and canals of arbitrary cross-section may be modelled. The method is best suited to displacement ships, including cargo ships, ferries, cruise ships, warships and superyachts.
Lifting Operations for Subsea Installations Using Small Construction Vessels and Active Heave Compensation Systems: A Simulation Approach
Authors: Halse Karl H. , Æsøy Vilmar , Ponkratov Dmitriy , Chu Yingguang , Xu Jiafeng , Pedersen Eilif
Published: September 2014

Sub-sea installation operations require a high level of accuracy and control in order to avoid misalignment and possible collisions between modules on the sea bed. To reduce costs, smaller and lighter construction vessels are now performing these operations. The most critical parts of the operation are lift-off from the deck, passing through the splash zone, and landing sensitive equipment on the sea bed. The hazards are: high dynamic loads, resonance effects, and slack line snap. Therefore, in this study, modeling and simulation are applied to optimize design parameters and develop operational procedures for each operation to reduce risk of failure. Further, the same models can be used in operator simulator training.

Modeling and simulation of interactive multi body systems is a rather complex task, involving the vessel as a moving platform, lifting equipment such as cranes and winches, guiding devices, lifting cables and payload behavior in air, all while partly to fully submerged. It is a multi-physics problem involving hydrodynamics, mechanics, hydraulics, electronics, and control systems. This paper describes an approach to link the different models to simulate the operations including interactions between the sub-systems. The paper focuses on the modeling approach used to connect the various dynamic systems into the complete operating system. The work is in its initial phase, and some of the sub-systems models are not complete. The models are described in this paper and will be included in future work. Some initial operational examples are included, to show how the models work together.
Lateral Buckling and Walking Design of a Pipeline Subjected to a High Number of Operational Cycles on Very Uneven Seabed
Authors: Solano Rafael F. , Antunes Bruno R. , Hansen Alexandre S. , Sriskandarajah T. , Charnaux Carlos R. , Ragupathy P. , Manso Daniel
Published: September 2014

Global buckling is a behavior observed on subsea pipelines operating under high pressure and high temperature conditions which can jeopardize its structural integrity if not properly controlled. The thermo-mechanical design of such pipelines shall be robust in order to manage some uncertainties, such as: out-of-straightness and pipe-soil interaction. Pipeline walking is another phenomenon observed in those pipelines which can lead to accumulated displacement and overstress on jumpers and spools. In addition, global buckling and pipeline walking can have strong interaction along the route of a pipeline on uneven and sloped seabed, increasing the challenges of thermo-mechanical design.

The P-55 oil export pipeline has approximately 42km length and was designed to work under severe high pressure and high temperature conditions, on a very uneven seabed, including different soil types and wall thicknesses along the length and a significant number of crossings. Additionally, the pipeline is expected to have a high amount of partial and full shutdowns during operation, resulting in an increase in design complexity. During design, many challenges arose in order to “control” the lateral buckling behavior and excessive walking displacements, and finite element analysis was used to understand and assess the pipeline behavior in detail.

This paper aims to provide an overview of the lateral buckling and walking design of the P-55 oil export pipeline and to present the solutions related to technical challenges faced during design due to high number of operational cycles. Long pipelines are usually characterized as having a low tendency to walking; however in this case, due to the seabed slope and the buckle sites interaction, a strong walking tendency has been identified. Thus, the main items of the design are discussed in this paper, as follows: lateral buckling triggering and “control” approach, walking in long pipelines and mitigate anchoring system, span correction and its impact on thermo-mechanical behavior.
Study of Tandem Offloading System for a New Concept Spar FPSO
Authors: Gao Wei , Qi Xiaoliang , Wang Jin
Published: September 2014

A new concept Spar FPSO (Floating Production Storage and Offloading) is proposed for South China Sea deepwater oil field development integrating the advantages of the deep-draft Spar concept whose excellent stability and global performance enables dry-tree drilling and production, and the conventional ship-shaped FPSO for oil storage and offloading.

This paper presents a study of the tandem offloading system for the new concept Spar FPSO. The paper will first give an overview of various offloading configurations and their characteristics for deepwater development; then a tandem offloading system similar to conventional ship-shaped FPSO is recommended for further investigation considering operational experience, safety and economical benefits. As the offloading operations are generally weather-limited, offloading environmental conditions for the study are selected based on API, ABS and South China Sea offshore operation practices. For a case study, hydrodynamic performance of the Spar FPSO in tandem offloading configuration with a shuttle tanker in 1500m water depth was investigated numerically and experimentally. Numerical simulations were conducted by means of fully coupled nonlinear time-domain analysis. The distance between the shuttle tanker and the Spar FPSO is optimized based on the relative motions of the two floaters and the hawser tension requirement of the shuttle tanker. Experimental results from model test are presented and compared with analytical time-domain simulation results. It is shown that the results of numerical simulations are consistent with the model test. The tandem offloading system demonstrates robust performance and cost-effectiveness for the proposed Spar FPSO concept.
Theory and Experiments of a Free-Running Fishing Vessel in Stern Sea
Authors: Thys Maxime , Faltinsen Odd Magnus
Published: September 2014

Hydrodynamic aspects of a modern fishing vessel during manoeuvring in a seaway was studied theoretically and experimentally. The focus was on small frequencies of encounter, corresponding to following and stern quartering seas, where fishing vessels are susceptible to capsize. The numerical model was based on de Kat and Paulling [1]. The model combined a 6 degrees of freedom (DOF) blended seakeeping model with a 4 DOF non-linear manoeuvring model. The 3D non-linear Froude-Krylov and restoring loads were computed by pressure integration up to the incident free surface. The added mass, damping and wave diffraction loads were obtained by generalizing the STF (Salvesen et al. [2]) strip theory to partly include 3D flow effects by means of WAMIT.

The simulated wave-induced surge forces over-estimated the experimentally measured forces by up to 50%. Excessive wave-induced surge forces led to predictions of broaching and surf riding, which did not occur in the experiments. Use of experimentally determined wave-induced surge forces gave good agreement between simulations and experiments.
Investigation of VIV Suppression Effect of the Finned Cylinder in Subcritical Flow
Authors: Wang Yongxue , Liu Xiaohua , Wang Guoyu , Ren Bing
Published: September 2014

The two-dimensional fluid-structure numerical model was developed to investigate the VIV suppression effect of the fined cylinder in subcritical flow (2000<Re<12000). The simulation of the flow field is performed by solving RANS equations with standard k-ε turbulence model. And the finned cylinder is modeled as a mass-spring system. The fluid-structure interaction of the finned cylinder in a uniform stream is numerically simulated by applying the displacement and stress iterative computation on the fluid-structure interfaces. The Arbitrary Lagrangian Eulerian (ALE) method and leader-follower method were combined together to keep a good quality of the fluid domain mesh for large displacements of fluid-structure interface.

The vortex induced vibration of smooth cylinder was firstly simulated and compared with the experimental and numerical results of available literatures.

The cylinder with Δ60-fins (consists of three splitter plates of 0.2D depth with splitter plate angle of 60° equally spaced on the cylinder surface) was investigated. The vortex shedding mode, vibration response, vibration frequency, and lifting force for the cylinder with Δ60-fins were analyzed and compared with smooth cylinder. The numerical results show that the cylinder with Δ60-fins can significantly interfere the vortex shedding and synchronization by reducing the lateral spacing of the initial large eddy. The remarkable decrease of response amplitude for cylinder with Δ60-fins is found.
Non-Linear Coupled Analysis for a Moored FPSO in Deepwater of the Gulf of Mexico
Authors: Torres Lopez Jaime , Tao Longbin
Published: September 2014

An accurate prediction of the global response of a floating production and storage offloading (FPSO) system under harsh environmental conditions is of great importance in order to achieve the reliability and safety operation of the whole system. FPSOs may be subjected to significant resonant oscillations in the horizontal plane due to low frequency (LF) wave effects and wind excitation forces. These characteristics may contribute to the increase in surge due to the low level of viscous hull damping. Additionally, it has been observed that when the water depth increases, the coupled effects (damping, inertia and restoring force) contributions from mooring lines and risers increases.

This paper investigates the LF response behavior of a deepwater FPSO unit in the Gulf of Mexico by carrying out a coupled analysis based on a nonlinear time domain analysis.

A 3D model based on boundary integrated element method is used to investigate the hydrodynamic behaviour of the floater as well as a 3D finite element model for each of the slender elements representing the mooring lines and risers. The LF motions of a FPSO with a typical arrangement of catenary mooring lines and steel catenary risers is studied for surge, sway and yaw mainly. The hydrodynamic characteristics of the FPSO are studied through both Newman’s approach and the full Quadratic transfer function.

The coupling effect of the floater and mooring/riser systems is examined by comparing the tensions in mooring lines/risers and the global responses of the system in six degree of freedom. The nonlinearity of the hydrodynamics of wave-vessel interaction and the dynamic contribution of mooring lines and risers are investigated with storm and hurricane events for a particular location in deep water Gulf of Mexico (GOM).
Drag Forces on, and Deformation of, Closed Flexible Bags
Authors: Lader Pål , Fredriksson David W. , Volent Zsolt , DeCew Jud , Rosten Trond , Strand Ida M.
Published: September 2014

The use of closed flexible bags is among the suggestions considered as a potential way to expand the salmon production in Norway. Few ocean structures exist with large, heavily compliant submerged components, and there is presently limited existing knowledge about how aquaculture systems with flexible closed cages will respond to external sea loads. The flexibility and deformation of the bag is coupled to the hydrodynamic forces, and the forces and deformation will be dependent on the filling level of the bag.

In order to get a better understanding of the drag forces on, and deformation of, such bags, experiments were conducted with a series of closed flexible bags. The bags were towed in a towing tank in order to simulate uniform current. Four different geometries were investigated, cylindrical, cubical, conical and pyramidal, and the filling levels were varied between 70% and 120%. The main findings from the experiments were that the drag force was highly dependent on the filling level, and that the drag force increases with decreasing filling level. Comparing the drag force on a deflated bag with an inflated one showed an increase of up to 2.5 times.
A Novel Data Processing Method for Ice Pressure Area Relations
Authors: Neumann Karoline M. , Ehlers Sören , Leira Bernt J.
Published: September 2014

An ice pressure data processing method based on definitions of basic, spatial and temporal events is described. The data processing method can be applied on a data set of semi continuous ice structure interaction observed with a finely meshed pressure sensing matrix with high sampling rates. An available data set satisfying these conditions from a model scale experiment in the Aalto ice tank is used to illustrate the application of the method. Using this novel processing method, each sample is associated with defined events, making it simple to produce various curves from the data set. Global and local, as well as spatial and process representations of pressure area curves are discussed, from design and ice research point of view. Finally four different pressure area curves are presented based on the application of the described processing method on the example data set. This processing methods aims to make extraction of results simpler for the designer and the scientist.
An Effective Approximation Modeling Method for Ship Resistance in Multidisciplinary Ship Design Optimization
Authors: Li Dongqin , Wilson Philip A. , Guan Yifeng , Zhao Xin
Published: September 2014

Ship design is related to several disciplines such as hydrostatic, resistance, propulsion and economic. The traditional ship design process only involves independent design optimization with some regression formulas within each discipline and there is no guarantee to achieve the optimum design. At the same time, it is crucial to improve the efficiency of modern ship design. Nowadays, the methods of computational fluid dynamics (CFD) has been brought into the ship design optimization. However, there are still some problems such as calculation precision and time consumption especially when CFD software is inlaid into the optimization procedure. Modeling is a far-ranging and all-around subject, and its precision directly affects the scientific decision in future. How to establish an accurate approximation model instead of the CFD calculation will be the key problem. The Support Vector Machines (SVM), a new general machine learning method based on the frame of statistical learning theory, may solve the problems in sample space and be an effective method of processing the non-liner classification and regression. The classical SVR has two parameters to control the errors. A new algorithm of Support Vector Regression proposed in this article has only one parameter to control the errors, adds b2/2 to the item of confidence interval at the same time, and adopts the Laplace loss function. It is named Single-parameter Lagrangian Support Vector Regression (SPL-SVR). This effective algorithm can improve the operation speed of program to a certain extent, and has better fitting precision. In practical design of ship, Design of Experiment (DOE) and the proposed support vector regression algorithm are applied to ship design optimization to construct statistical approximation model in this paper. The support vector regression algorithm approximates the optimization model and is updated during the optimization process to improve accuracy. The result indicates that the SPL-SVR method to establish approximate models can effectively solve complex engineering design optimization problem. Finally, some suggestions on the future improvements are proposed.
Use of Technology Qualification in Offshore Oil and Gas Operations: An FMECA Analysis for Mitigating Potential Failures
Authors: Ratnayake R. M. Chandima , Samarakoon S. M. Samindi M. K. , Gudmestad Ove T.
Published: September 2014

The implementation of new technology introduces uncertainties. Due to the consequence of failures, these uncertainties generate risks for the technology developers, manufacturers, vendors, operators and end-users. In this context, the application of proven technology in a new environment is also considered as new technology. In essence, a system as a whole is considered to be new technology when it has been assembled in a novel way consisting of individual components built using proven technology. The concerns in deploying new technology are significant in offshore oil and gas (O&G) operations, as they involve hazardous procedures. Moreover, technology is considered new when applied to offshore O&G operations due to the variability of technical challenges from field to field and the complexity of systems with limited space and experience in a harsh and sensitive environment. When new technology is integrated into a large system, it is necessary to evaluate the effect on the total system’s reliability in order to increase the level of confidence via a technology qualification procedure. Hence, it is vital to interpret how the risks are managed by the provision of evidence to reduce uncertainties. This manuscript presents an illustrative case of failure mode, effect and criticality analysis (FMECA) in qualifying new technology when it is implemented in an unfamiliar environment.
Tandem Riser VIV Suppression Fairing Model Test
Authors: Ng David Jinq Tyng , Teng Yih Jeng , Magee Allan , Bhat Aramanadka Shankar , Ahmad Zukni NorBahrain , Abdul Malik Adi Maimun , Abd Kader Ab Saman , Ismail Nasrudin Haji , Abdul Ghani Mohamad Pauzi
Published: September 2014

In deepwater development areas of Southeast Asia, the current is strong and relatively more persistent compared to other deepwater regions. Top tensioned risers (TTR) are critical submerged components of offshore platforms, constantly exposed to currents. These currents cause unsteady flow patterns around the risers i.e. vortex shedding. When the vortex shedding frequency is near the riser’s natural frequency, undesirable resonant vibration of the riser also known as Vortex Induced Vibration (VIV) occurs. Several types of VIV suppression devices are used in the offshore industry. Among them, the U-shaped fairing claims to have the capabilities of reducing VIV effectively as well as lowering drag loads.

This study investigates the effectiveness of a U-shaped fairing in suppressing riser VIV. The model test was successfully performed in a towing tank facility located at Universiti Teknologi Malaysia (UTM), Johor Bahru, Malaysia. This study is a significant collaboration between a local academic institution and the offshore oil and gas industry, aligned with the industry’s initiative of increasing local capabilities for research and development.

In this study, the VIV of two risers in tandem is simulated using scaled test models. The current flow is simulated by towing the vertically submerged test models with a moving carriage. The riser with fairing models are attached to a pair of custom-designed test rigs which are able to measure the forces and also allow movement of the test model during towing tests. The two test rigs are attached to a steel structure under the carriage which accommodates different tandem riser configurations and spacings. Two different sizes of risers and fairings are tested to check for Reynolds number effects.

For each tandem riser configuration, three different riser conditions are tested, i.e. (a) bare risers without fairings; (b) risers with weathervaning fairings, and (c) upstream riser with fairing stuck at different orientations and downstream riser with weathervaning fairing. The test results show significant reduction in drag and VIV for the risers with weathervaning fairings in different tandem configurations. Interesting motion characteristics are shown in some of the stuck fairing cases highlighting the adverse effects should the fairings fail to perform normally in the field.

Effective mitigation of VIV in risers using fairing suppression devices could lead to improved riser fatigue life and overall a more economical platform design. These benefits are highly applicable to local deepwater developments for the oil and gas industry.
Long Pile Upending Lifting Study for Fixed Platform on Offshore Oil and Gas Field
Authors: Zhou Yandong , Wang Facheng
Published: September 2014

Fixed platform have been widely employed in the offshore oil and gas reservoirs development. Pile foundation reliability is critical for these platforms where drilling, production and other functions are integrated. The lifting operation for the long pile, being a key step in the jacket installation, has been considered for further developments. With deep water developments, the sizes and weights of long piles are reasonably bigger. The corresponding process and equipment employed are subsequently altered, which brings challenges to developing a cost-effective, easy-operable approach for lifting operation. In this paper, the technology for the offshore long pile upending lifting operation including pile feature, installation methodology, lifting rigging and analysis model, covering water depths ranging from shallow to near deep water zone (60–300 m water depth) has been suggested. In addition, the applicability of the adoptable novel approaches has been discussed considering the practical project experience.
On the Effects of Bending Stiffness for Flexible Riser Model Tests
Authors: Ruskin Alex , Tahana Zak , Chai Shuhong , Balash Cheslav , Morand Henri , Izarn Cecile
Published: September 2014

Oil and gas production systems are continually moving into more challenging environments. Therefore having a precise understanding of the flexible pipeline behaviour for various configurations is becoming even more important. This paper presents a medium scale test of a flexible riser in a wave configuration aiming at representing the bending stiffness characteristic of a flexible riser. Results are then compared tothose of a dynamic analysis software to validate the experimental modeling.

This paper addresses the problem of scaling a flexible steep wave riser for model tests, where the global bending response is considered under quasi-static current loading. A methodology for cost-effective and robust model construction is presented, including an effective method of determining the bending stiffness of the model.

A 1/15 scale model of a 8″ flexible riser was constructed from silicon hose and foam for testing within the Australian Maritime College’s Circulating Water Channel (CWC). Variances in the model’s buoyant section length, system offset and bending stiffness were tested at different flow velocities to observe the changes in curvature experienced by the riser. The model test regime was formulated specifically to compare the results of CWC testing with numerical modelling results. Comparison between model test and numerical results demonstrate good agreement.
Preliminary Study on Stick-Slip in Drillstring With Analytical Model Expressed With Neutral Delay Differential Equation
Authors: Inoue Tomoya , Katsui Tokihiro , Rheem Chang-Kyu , Yoshida Zengo , Matsuo Miki Y.
Published: September 2014

Stick-slip is a major problem in offshore drilling because it may cause damage to the drill bit as well as crushing or grinding the sediment layer, which is crucial problem in scientific drilling because the purpose of the scientific drilling is to recover core samples from the layers.

To mitigate stick-slip, first of all it is necessary to establish a model of the torsional motion of the drill bit and express the stick-slip phenomenon. Toward this end, the present study proposes a model of torsional waves propagating in a drillstring. An analytical model is developed and used to derive a neutral delay differential equation (NDDE), a special type of equation that requires time history, and an analytical model of stick-slip is derived for friction models between the drill bit and the layer as well as the rotation speed applied to the uppermost part of the drill string. In this study, the stick-slip model is numerically analyzed for several conditions and a time series of the bit motions is obtained. Based on the analytical results, the appearance of stick-slip and its severity are discussed.

A small-scale model experiment was conducted in a water tank to observe the stick-slip phenomenon, and the result is discussed with numerical analysis. In addition, utilizing surface drilling data acquired from the actual drilling operations of the scientific drillship Chikyu, occurrence of stick-slip phenomenon is discussed.