bluuebunny/crossref_metadata_2025_split huggingface dataset:
Viscoelastic Behaviour of Bitumen in Dynamic Control Umbilicals
Authors: Olsen Elise , Hansen-Zahl Kay André , Karlsen Stian 
Published: September 2014

By combination of elements like hydraulic tubes, electrical and optical signal cables and electrical power cables, umbilicals provide remote control of subsea oil and gas wells. For extra tensile strength and outer protection the umbilicals may be armoured by galvanized steel wires. Dynamic umbilicals are terminated at offshore platforms or vessels. They are exposed to tension and bending variations caused by waves and vessel motions. As such a project specific analysis is normally required to verify that a given dynamic umbilical design with all its elements is able to withstand a service life of typically 20–30 years [5].
Understanding how forces are transmitted between the elements in an umbilical is vital for correct calculation of a dynamic umbilical design life. Cross section analysis is therefore performed by a finite element method program specially designed for this purpose. This software takes into account all effects in an umbilical cross section, including friction between elements. For solid elements, commonly known friction factors may be applied. However, for the steel wire armour which is corrosion protected by bitumen, the friction factors may not be valid. The force transmission between the steel wires may not be governed by friction but by the viscoelastic properties of bitumen. In such a case the transition force is not only a function of contact pressure but also of sliding velocity and dimensions.
A project was therefore initiated with the aim of describing such force transmission between bitumen and steel wires for typical umbilical conditions. Material testing has included characterization by a controlled stress rheometer and cyclic tensile testing at various temperatures, speeds and geometries. On basis of these tests, a calculation model describing the mechanical behavior of bitumen in cyclic movement is suggested. This model may later be implemented in the umbilical cross section analysis program.
Dynamic Responses of a Semi-Type Offshore Floating Wind Turbine
Authors: Li Liang , Hu Zhiqiang , Wang Jin , Hu Qiuhao 
Published: September 2014

This paper deals with wave-wind induced global motion and mooring system responses of a semi-type offshore floating wind turbine. The analysis in this paper is conducted in time domain, using an aero-hydro-servo-elastic simulation code-FAST. Due to the limitation of the initial drag force model in FAST, a quadratic damping model is developed to gain a better consideration of viscous performance. Simulations involve free-decay in still water, dynamic responses in moderate sea states with and without wind. Aerodynamic effects on platform dynamic responses are investigated.
Analysis indicates that wind force would accelerate platform’s decay motion and increase natural periods of surge and pitch, while heave motion is little influenced. Pitch motion is decreased at wave frequency range under joint wave-wind loads condition. Little wind-induced pitch resonant response has been observed. Nevertheless, instabilities are induced for surge motion due to negative aerodynamic damping. A typical mooring line force is found to be greatly excited by wind force.
Code Verification of ReFRESCO With a Statistically Periodic Manufactured Solution
Authors: Eça Luís , Vaz Guilherme , Hoekstra Martin 
Published: September 2014

This paper presents a Code Verification study performed with the unsteady ensemble-averaged Navier-Stokes (URANS) solver ReFRESCO using the Method of Manufactured Solutions. The study uses a statistically periodic manufactured solution including the un-damped eddy-viscosity of the Spalart & Allmaras turbulence model. Three main aspects of the numerical calculations of unsteady flows are addressed in this study: iterative errors; discretization errors (space and time) and the determination of the observed order of (space and time) convergence.
The availability of an exact solution allows the determination of the numerical error and so the effects of iterative and discretization errors can be addressed. The paper presents grid and time refinement studies with different (iterative) convergence criteria and demonstrates that grid and time resolution are strongly connected when attempts are made to minimize the numerical uncertainty in the calculation of unsteady flows.
The paper also addresses error estimation based on power series expansions in the calculation of unsteady (space and time dependent) flows. Simultaneous grid and time refinement is compared to grid refinement with fixed time step and time refinement with fixed grid. The advantages and limitations of both options are discussed in the context of Code Verification (error evaluation) and Solution Verification (error estimation).
A Comparison of Two Coupled Model of Dynamics for Offshore Floating Vertical Axis Wind Turbines (VAWT)
Authors: Borg Michael , Wang Kai , Collu Maurizio , Moan Torgeir 
Published: September 2014

As part of the deployment of floating offshore wind turbines (FOWTs) in deep sea, robust coupled dynamic design codes based on engineering models are being developed to investigate the behaviour of FOWTs in the offshore environment. The recent re-emerging interest in vertical axis wind turbines (VAWTs) for floating foundation applications has resulted in a number of design codes being developed concurrently by different researchers. In this study, two such design codes for floating VAWTs developed at Cranfield University and the Norwegian University of Science and Technology are compared through a series of increasingly complex simulation load cases.
A floating VAWT design was specified to be used in this study. The rotor is based on the Darrieus Troposkein shape and is the same used within the DeepWind VAWT spar concept, with a 5MW rated capacity. The floating support structure is a semi-submersible that is being used in the Offshore Code Collaboration Continuation (OC4) Phase II project for floating horizontal axis wind turbines.
A series of load cases were set out to assess and compare the two different design codes. A comparison of the performance of the two design tools is presented, illustrating their level of maturity and areas of improvement.
CFD Simulation of Propeller and Tunnel Thruster Performance
Authors: Lu Ping , Wang Sue 
Published: September 2014

In the present study, the hydrodynamic performance of a typical North Sea dynamic positioning (DP) shuttle tanker consisting of two main propellers, two rudders, and two bow tunnel thrusters is investigated by solving Reynolds-averaged Navier-Stokes (RANS) equations for a viscous flow. The focus of the numerical simulation is on the performance of propellers/rudders and bow tunnel thrusters considering the hydrodynamic interactions between propellers/thrusters, hull and current. The numerical model includes hull, propeller, rudder, bow tunnel thruster and flow field.
First, an analysis of a propeller performance in open water is carried out by calculating the coefficient of thrust, torque, and propeller efficiency. Then, rudders are included in the analysis for the assessment of propeller/rudder performance. The pressure distribution on rudders, rudder’s drag and lift coefficients for different angles of attack, and flow field around the rudder are obtained. The interaction effects between propeller, rudder, ship hull, as well as bow tunnel thruster and ship hull are analyzed by adding detailed ship hull geometry in the computational domain. The tunnel thruster efficiency reduction due to current and ventilation is also analyzed. The presence of current leads to significant changes in the flow velocity and distribution of pressure in the tunnel outflow area as well as significant deflection of the propeller jet emitting from the tunnel. A comparison between Computational Fluid Dynamics (CFD) and model test results of flow features near the tunnel area with various current speeds is presented.
Dropped Object Analysis Using Non-Linear Dynamic FE Analysis
Authors: Ahn Kwanghyun , Chun Minsung , Han Sangmin , Jang Kibok , Suh Yongsuk 
Published: September 2014

For the last few decades, necessity of direct non-linear FE analysis has been increasing for the accidental events at the vessel/offshore structures. One of major areas for the accidental design, dropped object analysis using non-linear analysis is indispensable for the verification of structural safety at the design process. This paper is concerned with the methodology, conditions, and design consideration of dropped object analysis using dynamic FE analysis. By comparing the results from direct FE analyses to those from simplified energy method described in DNV-RP-C204, necessities and advantages of direct non-linear analysis can be verified.
In this paper, the effect of analysis condition is investigated using parametric study. The results are influenced by the application of failure criteria according to the rule requirements, application of material properties, dropping position, condition of the object, and so on. This study can suggest appropriate determination of the methodology and condition for the dropped object analysis using direct FE analysis.
Marine Growth on North Sea Fixed Steel Platforms: Insights From the Decommissioning Industry
Authors: Mallat Chadi , Corbett Alistair , Harris Glyn , Lefranc Marc 
Published: September 2014

It is reputed in the Oil & Gas industry that marine growth is overestimated in the North Sea. Can we quantify this overestimation to better tackle the challenges marine growth incurs?
This paper provides insight into the intrinsic and diverse nature of marine growth. It documents the biofouling development and the factors that affect it globally. Focus is made on fixed steel platforms in the North Sea approaching the end of their economic lives. A methodology to quantify the weight of marine growth is proposed and illustrated. 28 years after its installation, the weight of marine growth accumulated on Valhall 2/4G jacket located in Southern North Sea is evaluated based on the proposed method. It is confirmed that the current regulations overestimate the weight of marine growth in the North Sea.
The Significance of Storm Avoidance on Macroscopic Fatigue Crack Growth
Authors: Hodapp David P. , Collette Matthew D. , Troesch Armin W. 
Published: September 2014

Ship weather routing is routinely employed to assist ship-masters in avoiding storms. During these storms, however, both material and hydrodynamic nonlinearities grow with the significant wave height (Hs). Hence, to fully understand the importance of weather routing, it may be necessary to go beyond a conventional spectral-based fatigue analysis which incorporates a linear damage hypothesis (i.e., the Palmgren-Miner rule).
To this end, the present paper examines macroscopic fatigue crack growth in which the nonlinear phenomena omitted in current design practices are included. We start by considering time-dependent ship structural loading sequences which include non-linear wave-induced bending and whipping responses taken from time-domain seakeeping simulations. These stresses are then analyzed using a fatigue crack growth model previously developed by the authors [1] in which material hysteresis is included using a mechanistic rather than phenomenological approach based on numerical simulations requiring only experimentally measured fatigue crack growth rates under constant amplitude cyclic loading (e.g., ASTM E647-13) and a full material constitutive model defined through experimental push-pull tests for the same material. Using this approach, we quantify the importance of weather routing by systematically substituting storms above a certain threshold with more moderate sea conditions.
A Numerical Model to Initiate the Icebreaking Pattern in Level Ice
Authors: Erceg Sandro , Ehlers Sören , von Bock und Polach Rüdiger , Leira Bernt 
Published: September 2014

Ships navigating in ice-covered waters experience local and global ice loads due to ice-hull interaction. The design of a ship with good ice performance requires adequate assessment of these forces. Recently, an increased activity in developing numerical models of ice-hull interaction in level ice has been observed, owed to the increased computational capabilities. However, certain semi-empirical icebreaking patterns inevitably influencing the interaction process have been implemented in the majority of interaction models used for the assessment of ice performance of ships. Therefore, an attempt using a quasi-static numerical approach to model the initiation of icebreaking pattern in level ice has been made and is presented in this paper. The term initiation herein denotes the creation of circumferential cracks, disregarding thus the succeeding radial cracks.
The concept used in the model features a set of radially oriented ice beams at the interaction zone. The model accounts for the bow geometry and the properties of the encountered ice. The icebreaking pattern for a case study ship is simulated using the developed model. Lastly, this paper discusses the sensitivity of the model with respect to the bow shape.
Snap Loads on Mooring Lines of a Floating Offshore Wind Turbine Structure
Authors: Hsu Wei-ting , Thiagarajan Krish P. , Hall Matthew , MacNicoll Michael , Akers Richard 
Published: September 2014

There are a number of design challenges facing mooring systems of floating offshore wind turbine (FOWT) platforms in an offshore environment. Some unique aspects of the FOWT industry should be considered when examining applicability of established offshore mooring practices. Important among these are: economy and cost effectiveness; light weight minimal platforms; and water depths ranging from 50–300 m. A lighter displacement platform in shallow water, supported by lines with light to moderate pre-tension can result in a higher probability of slack line events and hence snap loads during re-engagement. Such loads can result in shock on the line material and considerably reduce the fatigue life. Such events have the potential to occur in various sea states, and not necessarily limited to extreme conditions. These conditions will be dependent on structure resonant motions, which are influenced by wind loads and moments, wave conditions and mooring line properties. Model tests of typical concepts for FOWT reported in literature have shown occasional slack line episodes.
This paper is a review of literature on snap load occurrence in marine applications, including lifting and lowering operations, ROV and diving bell operations. This paper presents a case study of a FOWT. Special focus is on mooring systems which are affected by impact load conditions. Criteria are reviewed and consequences are documented.
Wave-in-Deck Forces on Fixed Horizontal Decks of Offshore Platforms
Authors: Abdussamie Nagi , Thomas Giles , Amin Walid , Ojeda Roberto 
Published: September 2014

The problem of wave-in-deck loading on offshore structures involves complex physical mechanisms which require close study. In this paper, the wave-in-deck forces generated on the bottom plate of a rigidly mounted, box-shaped structure subjected to unidirectional regular waves are quantified by means of two approaches. The first is an analytical momentum approach recommended by classification societies and the second is a computational fluid dynamics (CFD) approach based on the volume of fluid (VOF) method implemented in the commercial code FLUENT. The change in force due to very small variations in wave steepness and air gap is investigated and discussed.
Several numerical trials are conducted to optimise the computational domain and model discretisation suggestions are made. The numerical results are compared with physical model tests recently carried out at the Australian Maritime College (AMC). The results of the successive wave impacts are analysed using a discrete wavelet tool to ensure that the temporal information of slamming events is not lost in signal analysis and filtering. By comparing the theoretical and experimental results it was found that in many cases the momentum method underestimates the magnitude of the horizontal and upward directed wave-in-deck forces. Although the three-dimensional CFD cases tested are noticeably time-consuming, these simulations were found to be in good agreement with the experimental measurements.
Experimental Assessment of the Behaviour of a Pipe Vibration Damper Underwater
Authors: Bordalo Sergio N. , Morooka Celso K. , Tochetto Luan G. , Pavanello Renato , Song Gangbing , Bartos John C. 
Published: September 2014

Submarine petroleum pipelines, risers and jumpers suffer static and dynamic loads due to sea currents and waves, due to the displacements of the floating production units and due to the internal flow, among other causes. Mitigating the oscillations caused by such excitations is critical to the reliability and fatigue of those underwater bodies. The Pounding Tuned Mass Damper (PTMD) is one device that may be employed to absorb and dissipate vibrations. These devices have long been used for mechanical systems operating in the atmosphere, but are new for underwater applications. This paper presents a study of the behaviour of a PTMD working underwater.
A small scale laboratory apparatus was built to assess the effect of the absorber on the oscillation of a pipe submerged in a water tank. The PTMD was attached to a test pipe section mounted on an elastic suspension harness. The PTMD model is a lumped mass-spring attachment similar to a tuned mass dumper (TMD) suppressor, but with the addition of a pounding layer, which limits the motion of the PTMD mass, dissipating the energy of the oscillating pipe through the impact of the PTMD mass against that layer. Free and forced oscillation experiments were executed in air and in water, with and without the oscillation absorber, to determine the effectiveness of the PTMD. The tests were run on a range of excitation frequencies and the amplification factors were obtained for each case.
The data show a remarkable influence of the surrounding media on the dynamics of the pipe-absorber system, therefore the interaction with the water must be taken into consideration in the design of the system. Although the results are only a preliminary step on the development of a device applicable to an actual petroleum submarine pipeline, it was observed that the PTMD does indeed suppress the vibrations, but it must be properly configured to achieve an optimum performance. The data gathered from this work will also be useful in the improvement of a numerical model of the pipe-PTMD system for use in a computer simulator.
A New Approach to Model Hyperbaric Rock Cutting Processes
Authors: Helmons Rudy L. J. , Miedema Sape A. , van Rhee Cees 
Published: September 2014

In deep sea mining processes, rock is being cut in a hyperbaric pressure environment. The effect of such a high pressure environment is of major influence on the cutting process. Due to deformation of the rock matrix, local fluid pressure differences will occur. This can result in a higher apparent strength of the rock, but also in a higher (loading) rate dependency.
Our new modeling approach aims at combining both rock mechanics and fluid dynamics to model the high deformation (rate) behavior experienced in seabed excavations. This new approach is based on the Discrete Element Method to simulate the rock mechanics, combined with the use of Smoothed Particle Methods to model the influence of the fluid (pressure) on and in the rock. In this paper, emphasis is put on estimating the local (volumetric) deformation rate with the new approach. Eventually, the new technique will be validated with experiments and data available in literature. The new approach will give more insight in the physical processes that occur during cutting.
Performance Evaluation of High Quality HFW Linepipe by a Series of Full-Scale Pipe Tests
Authors: Igi Satoshi , Sadasue Teruki , Oi Kenji , Yabumoto Satoru , Toyoda Shunsuke 
Published: September 2014

Newly-developed high quality high frequency electric resistance welded (HFW) linepipes have recently been used in pipelines in reel-lay applications and low temperature service environments because of their excellent low temperature weld toughness and cost effectiveness. In order to clarify the safety performance of these HFW linepipes, a series of full-scale tests including a hydrostatic burst test at low temperature, fatigue test and tension test under high internal pressure was conducted, together with small-scale tests such as impact energy and standard fracture toughness tests, which are generally used in mill production and pre-qualification tests.
The Charpy transition curve of the developed HFW pipe occurred at a temperature much lower than −45°C. Based on the low-temperature hydrostatic burst test with a notched weld seam at −45°C, the weld of the HFW linepipe presented the same level of leak-before-break (LBB) behavior, as observed in UOE pipes. A full-pipe fatigue test of HFW pipes with repeated internal pressurizing was conducted. The fatigue strength of the developed HFW linepipe shows better performance than butt weld joints because of the smoothness at its weld portion, which is achieved by mechanical grinding of the weld reinforcement. Full-scale pipe tensile tests of girth welded joints were performed with an artificial surface notch at the heat affected zone in the girth weld. The influence of internal pressure was clearly observed in these tests.
Based on the above-mentioned full-scale tests, the safety performance of high quality HFW linepipe is discussed in comparison with the mechanical properties in the small-scale tests such as the Charpy and standard fracture toughness tests, especially when the notch was placed in the welded seam.
Modeling Stalk-On Operation and its Application
Authors: Hong Jin Wuk , Kim Jong Wook , Kim Kyu Tae , Lee Woo Seob 
Published: September 2014

Tie-in between a pipeline and a riser is an important operation in the offshore oil and gas development. Normally, divers need to carry out the tie-in operation on the seabed by welding or using flanges in order to connect the pre-laid pipeline end to the jacket riser. However, working on the seabed can have leakage or cost problems. As one of solutions, the surface-tie-in method so called stalk-on method is used in the shallow water. In this method, the riser is welded to the pipeline which is lifted over the sea surface, and the welded pipeline-riser is lowered to the target position.
The main purpose of this paper is to demonstrate the safety evaluation procedure of the stalk-on operation and to share the experience learnt from actual field application. For the sake of the safety evaluation, the stalk-on operation is divided into 3 phases which are the phases of lifting a pipeline by davit cranes, holding a lifted-pipeline and lowering the weld-connected pipeline and the riser. Each phase is numerically simulated in time-domain analysis. The several lesson learnt from actual application are summarized including the consideration of discrepancy between time domain simulation result and the measured one during the installation.