bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of Stress Transfer Functions for Wellhead Fatigue
Authors: Williams Dara 
Published: October 2015

In many harsh environment or high current regions (e.g. West of Shetlands, East Africa and GoM) wellhead fatigue during drilling or workover activities can be a major concern. As a result extensive wellhead and conductor fatigue assessments are required in order to predict likely fatigue damage prior to landing the BOP on to the wellhead. These pre-drilling or predictive studies are based on a number of assumptions regarding actual environmental and soil conditions. In addition the uncertainty associated with the input data requires safety factors of 10 and 20 for wave and VIV effects respectively. As a result of these assumptions the predicted levels of fatigue damage to the wellhead may be highly conservative. In cases where wellhead and conductor fatigue life is a concern the operator may choose to deploy motion monitoring systems on the BOP stack so that actual fatigue loads recorded during drilling can be calculated. These systems can be configured to provide ‘real-time’ updates on fatigue damage accumulation or can be used to record data for ‘post-drilling’ assessment. In each case the methodology applied to calculate stresses at fatigue hotspots is critical to the calculation of overall fatigue damage.
The calculation of fatigue loads based on measured data is typically carried out by applying the measured BOP motions to a global finite element model of the drilling riser and wellhead system. However due to the large amounts of data involved this can be a very time consuming exercise and is not conducive to ‘real-time’ presentation of results (e.g. for on-board systems). A proposed solution to this problem is to develop stress transfer functions (STFs) that relate BOP motion to stresses at critical fatigue hotspots. Thus ‘real-time’ BOP motions and be instantly converted to ‘real-time’ stresses. However, as is outlined in this paper, the frequency content of the system response can have a significant impact on the levels of stress calculated. If frequency dependent response is not accounted for a significant under-prediction in fatigue loads may occur.
The objective of this paper is to outline a detailed methodology to derive STFs for critical fatigue hotspots in the wellhead and conductor. This methodology accounts for capturing the non-linear frequency dependence of the system and incorporating this into the STFs. In addition a methodology for rapidly calculating ‘real-time’ fatigue damage accumulation in the wellhead and conductor system and presenting this data on-board is also outlined.
Estimating Long Term Extreme Slamming From Breaking Waves
Authors: Lian Gunnar , Haver Sverre K. 
Published: October 2015

Characteristic loads for design are defined in terms of their annual exceedance probability, q. For ultimate limit state (ULS) q = 10−2, while q = 10−4 for accidental limit state (ALS). In principle a full long term analysis is required in order to obtain consistent estimates. This is straight forward for linear response problems, while it is a challenge for non-linear problems in particular if they additionally are of an on-off nature. The latter will typically be the case for loads due to breaking wave impacts.
The Contour line approach is an alternative convenient method to estimate the long term extreme response, based on short term statistics from an appropriate sea state. The consequence of very large short term variability (large coefficient of variation for 3-hour extreme value) on the application of the contour method will be discussed.
The long term integral is carried out over all sea state combinations. The lowest sea states will of course not affect the extremes. However, for the impact problem the short term variability is much larger than for most response cases. The coefficient of variation of the 3-hour maximum impact pressure is often between 0.5 and 1, while for a typical response process it is between 0.1 and 0.2. Due to the large variability, lower sea states than normal will contribute to the long term response.
In this paper the irregularity of the response surface, and the uncertainties related to the number of seeds used in each sea state is looked into. The focus is on slamming loads from breaking waves, and some results from a model test are presented. The uncertainties in long term response from slamming loads are compared to a more common response process. The effect on the long term response when integrating over a reduced area of sea states in the scatter diagram is discussed.
Hydrodynamic Analysis of an Inverted Catenary Coldwater Pipeline of a LTTD Plant
Authors: Ajeesh M. V. , Selvam R. Panneer , Sundarvadivelu R. , Dhinesh G. , Saravanan R. , Phani Kumar S. V. S. , Ramana Murthy M. V. 
Published: October 2015

Drinking water is a precious commodity with growing demand, motivating the researchers to explore innovative and cost effective measures to augment the available resources. Low Temperature Thermal Desalination (LTTD) is one among the ideas that utilizes the ocean thermal gradient for the production of freshwater. The cold water from deep sea is drawn and transported to the coast or to a floating platform to aid the conversion of surface seawater to fresh water. The behavior of this cold water pipeline in open waters is to be studied through analytical, numerical and experimental studies before actual field implementation.
This paper presents the preliminary analysis of a flexible cold water pipe made up of High Density Polyethylene (HDPE) catering for an island based desalination plant. The water is drawn at a depth of 400 m and transferred to the shore. The site with coral reef demands an inverted catenary profiled pipeline to minimize damages and is connected to sump at the shallow end and a clump weight at the deep end. Preliminary hydrodynamic analysis of the cold water pipeline is carried out using OrcaFlex software under regular waves. Obtaining the effect of flexible pipeline under regular waves besides carrying out vortex induce vibration analysis and modal analysis forms the scope of this study. Variation of VonMises stresses, and effective tension at salient points (top end, middle and bottom end) are included.
Rotor Scaling Methodologies for Small Scale Testing of Floating Wind Turbine Systems
Authors: Martin Steven , Day Sandy , Gilmour Conor B. 
Published: October 2015

Two scaling methodologies are presented to address the dissimilitude normally experienced when attempting to measure global aerodynamic loads on a small scale wind turbine rotor from a full scale reference. The first, termed direct aerofoil replacement (DAR), redesigns the profile of the blade using a multipoint aerofoil optimisation algorithm, which couples a genetic algorithm (GA) and XFOIL, such that the local non-dimensional lift force is similar to the full scale. Correcting for the reduced Reynolds number in this manner allows for the non-dimensional chord and twist distributions to be maintained at small scale increasing the similitude of the unsteady aerodynamic response; an inherent consideration in the study of the aerodynamic response of floating wind turbine rotors. The second, the geometrically free rotor design (GFRD) methodology, which utilises the Python based multi-objective GA DEAP and blade-element momentum (BEM) code CCBlade, results in a more simplistic but less accurate design.
Numerical simulations of two rotors, produced using the defined scaling methodologies, show an excellent level of similarity of the thrust and reasonably good torque matching for the DAR rotor to the full scale reference. The GFRD rotor design is more simplistic, and hence more readily manufacturable, than the DAR, however the aerodynamic performance match to the full scale turbine is relatively poor.
The Influence of Pipeline Bending Stiffness on 3D Dynamic On-Bottom Stability and Importance for Flexible Flowlines, Cables and Umbilicals
Authors: Robertson Matthew , Griffiths Terry , Viecelli Graham , Oldfield Stuart , Ma Peter , Al-Showaiter Aiman , Carneiro Daniel 
Published: October 2015

In some areas of the world, subsea pipeline hydrodynamic stability is one of the most fundamental aspects of pipeline design. Several design approaches can be used to analyse pipeline stability, ranging from simple force-balance calculations to complex dynamic finite element analysis. Effective and accurate pipeline stability analysis is essential to avoid the potentially high costs associated with complex stabilisation solutions.
As it stands the current engineering practices using absolute stability or generalized stability do not explicitly account for pipeline stiffness, hence do not distinguish any difference in response between flexible and rigid pipelines of similar SG and diameter under a given metocean condition.
Observations of recent WGK dynamic stability analyses show that pipelines that have identical properties but very different stiffness will exhibit significantly different lateral response under the same metocean conditions.
Studies investigating sensitivity of predicted lateral response versus the number of storm random seed realisations have also been observed to show little or no correlation between the peak wave velocity and peak pipeline response.
Recognising that in directionally spread wave conditions, peak wave events do not tend to be associated with the widest wave crests in a seastate, this paper will investigate the nature of wave velocity and crest width characteristics leading to pipeline lateral displacement events (width and net movement) within a storm, and how this varies with pipeline stiffness.
Further understanding of the mechanisms driving pipeline response are therefore expected, based on the hypothesis that both pipeline stiffness and the crest width of waves capable of causing pipeline displacement are important parameters. It is further anticipated that this will help refine the existing design approaches for flexible pipelines which may not be adequately addressed using existing industry design methods, as well as providing recommendations for the minimum length of 3D dynamic stability models required to be considered in order to accurately capture the longitudinal length scales of importance.
Utilization of Wave Dissipating Caissons as an OWC Type Wave Energy Convertor
Authors: Ikoma Tomoki , Masuda Koichi , Eto Hiroaki , Kihara Kazuyoshi , Maeda Hisaaki , Takahatake Madoka 
Published: October 2015

Wave energy convertors (WEC) of oscillating water column (OWC) types make compressed air due to vertical movement of a part of water column, which are surrounded by some walls in water. As a result, the compressed air works to rotate an air turbine which also works for an electrical generator. If a structural system can make to move water such like a water column, a shape of a structure would not matter.
Wave dissipating caissons installed in or on the existing production line can make to transfer a water wave to a flow and to reduce wave energy by making to overflow them. The caissons which can be overflowed by the water would actuate a water region vertically such like an oscillating water column system.
This study investigated if we can utilize wave dissipating caissons as a WEC. Wave dissipating caissons also decrease wave energy due to passing through themselves. Even so, when an air turbine can be installed onto the caisson in order to harvest wave energy, it would be possible to produce electricity at low cost. The study conducted model experiments using the model assumed that wave dissipating double-caissons were remodelled to OWC type WECs with side walls and evaluated performance of the primary conversion of them. In addition, effects of how to arrange the number of the WECs on the primary conversion efficiency were investigated with theoretical calculations based on the linear potential theory and the possibility of utilization of wave dissipating caissons as a WEC was examined in the study.
Efficient Fatigue Testing of Tubular Joints
Authors: Thibaux P. , Van Wittenberghe J. , Van Pottelberg E. , Van Poucke M. , De Baets P. , De Waele W. 
Published: October 2015

Tubular joints are intensively used in off-shore structures for shallow waters. Depending on the sea conditions and the type of structure, the design can be fatigue driven. This is particularly the case for off-shore wind turbines, where turbulences are generating a fatigue loading. Any improvement of the fatigue performance of the tubular joint would be beneficial to reduce the weight and the cost of the structure. To assess efficiently the fatigue resistance of the tubular joint, a testing method has been developed based on the resonance principle. The complete circumference of the welded joint can be loaded, successively in the in-plane and out-of-plane modes at a frequency close to 20Hz.
Finite element computations were used to investigate the feasibility of the concept. Then, an X-node was made and successfully tested to investigate the stress distribution along the weld. The experimental results were compared with finite element computations, giving a good agreement.
Influence of Structural Compliance and Slope Angle on Ice Loads and Dynamic Response of Conical Structures
Authors: Ziemer Gesa , Evers Karl-Ulrich , Voosen Christian 
Published: October 2015

Model tests in ice have been conducted at the Large Ice Basin of HSVA with cylindrical and conical, compliant structures exposed to drifting level ice to investigate the influence of slope and compliance on the ice load and its breaking frequency. Main goal of the test campaign was to study the importance of structural feedback during ice-cone interaction. This is a major issue e.g. for numerical simulation of offshore structures during design phase. Four shapes were tested: 50°, 60°, 80° and 90° slope angle. The cylinder was tested in order to define the worst case scenario regarding magnitude of ice load and severity of ice-induced vibrations. Stiffness and natural frequency of the structure were chosen similar to typical values for offshore wind turbine support structures. All shapes were tested both in a compliant and fixed configuration.
The breaking frequency was found to be more pronounced for the lower slope angles where the ice failed in flexural failure only, while a transition to crushing failure as observed on a cylindrical structure takes place at 80° cone angle already. This results in significantly higher ice loads on the 80° cone than on those with lower angles, but a reduced risk of severe ice-structure interaction due to the unsteady nature of the mixed mode breaking process. Although the breaking frequency is rather constant e.g. during ice impact on the 60° cone, it was not possible during the model tests to match the ice drift speed and the dynamics of the structure in a way that causes resonance. However, model test results prove that there is a risk of conical structures with low natural frequencies and low stiffness in ice plane being excited by periodic ice failure in their natural frequency, thus response amplification may take place and pose a risk to the structural integrity of conical offshore structures exposed to sea ice.
This paper presents the model test setup, analysis of the results, and general findings.
Global Buckling Mitigation of Buried Pipelines: Lateral Resistance Assessment
Authors: Gallegillo Martin , Hardouin Guillaume 
Published: October 2015

This paper presents an approach to rock cover design for un-trenched pipelines installed on the seabed and rock-dumped for protection against dropped objects, anchor chain impact and fishing/trawling activities. This is found in some North Sea locations which present challenging conditions for trenching while protection is necessary due to intensive fishing activities.
Under these circumstances the pipeline must remain within the rock berm and, hence, it must be designed against global buckling. Whereas there are clear design guidelines addressing upheaval buckling behaviour, the resistance to lateral buckling to maintain a pipeline within the rock berm has received less attention in the literature.
The aim of this paper is to present a method to design a rock berm to mitigate against lateral buckling of rock-dumped pipelines based on the horizontal out-of-straightness survey data provided to the designer. The main challenges associated with this activity at different design phases are also introduced, including the use of analytical tools as well as detailed finite element analysis.
Distributed Propulsion: A Novel Concept for Inland Vessels
Authors: Hagesteijn Gerco , van der Meij Karola , Thill Cornel 
Published: October 2015

In the drive to reduce the fuel consumption of inland vessels, one of the main limitations, the risk of propeller ventilation was investigated. The aim was to reduce the resistance of the vessel, while at the same time an acceptable margin against propeller ventilation had to be assured. A typical inland vessel has up to two high loaded relative large propellers, with tip regions in the lighter loading condition above the water line. To eliminate the risk of propeller ventilation, these ships often have inbuilt shape features such as tunnels and skirts, only having the intention to avoid air being drawn by the rotating propeller.
These devices however have a noticeable own resistance, imposing a mortgage to the ship’s total resistance. Current design practice for these devices is that as long as you cannot quantify a risk, take care of a sufficient safety margin. With the research done within the EU-funded STREAMLINE project new insights were gained into the prediction of air suction. As a result, the margin against ventilation could be reduced which resulted into a large reduction of the resistance of the vessel.
Reducing the high loading of propellers means to gain efficiency with at the same time reducing the risk of propeller ventilation as the suction by the propeller(s) can be decreased as well. This leads to the idea of a “distributed thrust” concept (DTC). Within STREAMLINE DST developed a sample case for such a novel design with six thrusters, with the aim to reduce ventilation against zero and to achieve maximal performance improvements. The measurements were carried out in MARIN’s Depressurized Wave Basin (DWB). These tests were carried out with a 1:10 scale ship model, in sailing condition, and depressurized conditions. In this way, the correct representation of cavitation and possible ventilation bubbles and vortices is ensured, resulting in a correct physical behavior. At the same time synchronized high speed video recordings were made to acquire insight in the occurring phenomena.
Within the project CFD calculations were carried out, aimed at characterizing the performance, loads, cavitation nuisance and ventilation risk in full-scale operating conditions. Validation of these calculations was done using the towing tank results.
Uncertainty of Sea Trials Results Used for Validation of Ship Manoeuvring Simulation Models
Authors: Gavrilin Sergey , Steen Sverre 
Published: October 2015

Increasingly complex marine operations dictate higher need for precise and reliable modelling. For the last decades several different approaches to modelling of ship manoeuvring were developed, including scaled model testing, numerical and empirical methods. Increasingly, time-domain simulation models for ship manoeuvring are developed and used for training and planning of marine operations. Especially when using the simulation models to plan operations, it is essential that the simulation model is properly validated. There is a need for better and more standardized validation methods for such simulation models. A key issue is the uncertainty of the data used in the validation. Typically, the validation will be against full scale trials results.
In the study reported in this paper it was found by inspection of repeated tests results that even under relatively calm environmental conditions outcomes of sea trials can be highly uncertain. However, it is very expensive to investigate uncertainty of each type of trial experimentally. Therefore it can be very beneficial to estimate it by means of a simulation model.
This paper presents results of analysis of full scale turning circle trials of research vessel “Gunnerus”. Turning circle trials with 20° and 35° rudder angle executed both to starboard and port sides are analyzed. Experimental uncertainty analysis is performed. Effectiveness of IMO correction procedure is discussed. Also paper describes a method for determining uncertainty of trial results due to environmental effects by means of simulation model and compares them with experimental uncertainty. The method is based on Monte-Carlo techniques.
Reduction of Tophole Risks Through Improved Application of Geophysical and Geotechnical Techniques
Authors: Barwise Andy , Salisbury Richard , Wood Gareth , Van Der Kraan Micha , Carrington Tim , Thompson Giles 
Published: October 2015

The offshore oil and gas industry spends over $60bn per year on oil and gas wells and of this some $6bn, or around 10% is eaten up by geological and geotechnical problems such as stuck pipe, lost circulation, well bore instability, shallow water flows and other problems. On top of this are the environmental costs of the oil spills that can result from lost well control, and perhaps most importantly the human costs in terms of injuries and loss of life resulting from some of the worst incidents.
This paper lists the geohazards within and around a well, the drilling risks implied by these geohazards, and the impact they can have on the planning and drilling of offshore wells.
Current practice in geophysical and geotechnical site investigation techniques which, when correctly applied and interpreted, can help to reduce the risks and costs associated with the ‘Top-hole’ section is summarised and discussed (the Top Hole section is defined as the depth to the base of the first pressure containment string).
Finally, a systematic approach to assessing and mitigating top-hole geo-risks through a multi-disciplinary geoscience and engineering approach is described.
The authors are members of a working group of the Offshore Site Investigation and Geotechnics (OSIG) committee of the Society of Underwater Technology (SUT) who are drafting guidelines on the subject.
State-of-the-Art Within Ship Weather Routing
Authors: Simonsen Martin Hjorth , Larsson Erik , Mao Wengang , Ringsberg Jonas W. 
Published: October 2015

Increased fuel prices and public awareness of environment impacts from shipping have attracted large efforts in maritime sector to increase its energy efficiency as a factor of competitiveness. Weather routing has become a recognized measure, which can partly help to achieve the targets as well as enhancing safety. A routing system requires a reliable optimization algorithm to consider a ship’s operational costs, expected time of arrival, and cargo safety etc. simultaneously. Hence, the service provided by a weather routing system is highly dependent on a properly selected optimization algorithm and associated input parameters.
In this paper the concept of weather routing is broken down into many elements for further analysis. Focus is given to algorithms, constraints and weather forecasts used in the optimized routing plan. Two different aspects of state-of-the-art have been considered. The first is a study of software already in use and the second is a study of methods investigated in the research community. Furthermore, this paper also provides examples of development trends, for example the fatigue based routing, and the risk based routing, as well as its integration with onboard monitoring systems for more reliable weather and ship specific response information.