bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
VolturnUS 1:8-Scale FRP Floating Wind Turbine Tower: Analysis, Design, Testing and Performance
Authors: Young Andrew C. , Hettick Steve , Dagher Habib J. , Viselli Anthony M. , Goupee Andrew J. 
Published: September 2014

In May of 2013 the VolturnUS 1:8 floating semi-submersible wind turbine was successfully deployed off the coast of Castine, Maine, making the unit the first grid connected offshore turbine in the United States. The VolturnUS 1:8 structure features a 20 kW turbine, a post-tensioned and reinforced concrete semi-submersible base and a fiber reinforced plastic (FRP) tower (E-glass and polyester resin). The VolturnUS 1:8 structure is a geometrically 1:8-scale of a 6 MW floating turbine design and is used to demonstrate the feasibility of both the concrete base and FRP tower and validate the performance of the structure in a scaled environment. Data collected from the deployed 1:8-scale structure will be used for modeling and simulating the behavior of the system at full-scale. The effort was led by the University of Maine’s Advanced Structures and Composites Center (UMaine) and a consortium of industry partners, including FRP manufacturer Ershigs, Inc.
An overview of the process and methodology used in the analysis, design and testing of the 1:8 scale FRP floating wind turbine tower is presented. The use of an FRP tower on a floating wind turbine platform offers the benefits of reduced tower mass and maintenance requirements and has the potential to further reduce hull mass by lowering the global center of gravity of the structure. An FRP tower for use on the UMaine semi-submersible concrete VolturnUS 1:8 platform was developed that meets all strength and serviceability criteria and is robust enough to withstand the loading from both wind and waves. An overview of the tower loads analysis and FAST modeling, tower structural design, structural proof testing and preliminary analysis of performance are presented.
The VolturnUS 1:8 wind turbine tower is the first time FRP materials have been used in an offshore wind tower application. Further, the methodologies and procedures that were developed in the design of the pilot-scale tower are directly applicable to the design and analysis of composite wind turbine towers at the full-scale level. These “lessons learned” are already in use as Ershigs and UMaine work to design a full-scale composite tower over 80 meters tall for use on the VolturnUS platform with a 6MW wind turbine. The results of the 1:8-scale program demonstrate the successful use of an FRP wind turbine tower on a floating platform and highlights the potential for the use of an FRP tower at the full-scale (6 MW) level.
Analysis of Wave Interaction With Cylinders Using a 3D Numerical Wave Tank
Authors: Kamath Arun , Bihs Hans , Arntsen Øivind A. 
Published: September 2014

Evaluation of flow around a cylinder placed in waves is a challenging task due to the complex nature of the flow. A good understanding of the flow physics involved here is important as coastal and offshore structures consist of horizontal and vertical cylindrical elements. This paper explores the use of Computational Fluid Dynamics (CFD) to evaluate the flow field around cylindrical structures. A 3D numerical wave tank is employed to study the free surface and fluid velocities around a vertical cylinder placed in waves and the total force acting on the cylinder is evaluated. The numerical results are compared with experimental data. Further, a simple representation of an offshore structure modelled as multiple cylinders in proximity is also simulated in the numerical wave tank. The presence of neighbouring cylinders has an effect on the flow field. This affects the force acting on each of the cylinders in the group. The forces acting on every cylinder in the group are evaluated and the free surface elevation in the flow field is also visualised. The numerical result is compared with the result from an analytical formula.
The numerical model uses the Reynolds-Averaged Navier-Stokes equations to evaluate the flow field. The convective terms are discretized using a 5th-order conservative finite difference WENO scheme. Time discretization is carried out using a 3rd-order Runge-Kutta scheme. Pressure discretization is carried out using Chorin’s projection method. The Poisson pressure equation is solved using a pre-conditioned BiCGStab algorithm. A sharp representation of the free surface is obtained using the level set method. Turbulence modeling is carried out using the k-ω model. Computational performance of the numerical model is improved by parallel processing using the MPI library.
Rate Dependent Soil Resistance in FE Analysis of Pipeline Walking
Authors: Carneiro Daniel , Rathbone Andrew , Soon Kok Siong , Viecelli Graham 
Published: September 2014

Pipeline walking is a complex phenomenon, governed by the axial pipe-soil interaction which is not yet fully understood, and which has been gaining increasing attention over the last few years. Axial friction (as any other aspect of soil mechanics) is usually bounded by drained and undrained responses, while in real life it will often be somewhere in the middle. For pipeline expansion it could be critical as while the ends might move a couple meters in the few hours it takes to heat up, somewhere close to the middle it will move a few millimeters only (so the level of drainage is totally different along the same line, during the same loading).
Geotechnical frameworks to address the different aspects governing the soil response to pipeline axial movement have recently been published. However, the current practice has been to lump all the time dependent effects back into a single equivalent friction factor, based on a representative pipeline velocity.
This paper presents the results of ‘true’ rate dependent pipeline walking analyses, and compares them to those obtained using constant equivalent frictions. While good agreement is observed for particular cases, differences up to 30% of the walking rate are observed. Examples show that the results of rate dependent pipeline walking analyses are significantly influenced by how the temperature changes over time along the pipeline length, thus realistic modeling of the heat up and cool down processes is crucial.
The rate dependent model employed describes the axial resistance as a hyperbolic function of the pipe velocity. Additional aspects which are expected to influence the soil response (e.g. consolidation time between sweeps, progressive compression and consolidation hardening) have been neglected, and shall be considered in further studies.
High Capacity Carousels: Modularity, Technical Development and Innovation
Authors: Tibbetts David , Dale Nicholas 
Published: September 2014

Marine installation operations are becoming ever longer, larger and deeper. With campaigns regularly being carried out in the 2,000–3,000m water depth range and tieback lengths on the increase; installation, replacement or recovery works for this specification of product requires specialist equipment that can accommodate the increasing bulk of the flexible products being installed, without compromising the performance of the vessels which carry them.
In order to fulfil this technical challenge, new and innovative carousel designs are being developed. Placing the ‘reel’ horizontally allows maximum product capacity whilst minimising the impact on the vessel, thus maintaining operational efficiency in both shallow and deep waters and for projects such as subsea tiebacks and connections to processing platforms and offshore installations.
This paper explores recent developments in technology, where product loads of up to 1,500Te (Tonnes) are frequently required and ever shorter schedules are placed on contractors for initial spooling and subsequent installation. Technical innovations, operational solutions and commercial advantages will be assessed and the ability to open up new markets with the technology on offer will be scrutinised.
Alongside this, the benefits of modularity are evaluated to quantify the advantages of being able to disassemble and transport this type of hardware worldwide and the vessel utilisation improvements that can be made.