bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Top-End Vessel Heave on Submarine Riser VIV of Deep Water Platform
Authors: Chen Weimin , Li Min , Guo Shuangxi , Gan Kuan 
Published: September 2014

The dynamic coupling between moving top-end vessel and submarine riser becomes more remarkable for a floating platform in deeper water due to the larger top-end motion amplitude, compared with the fixed platform in shallow water. In this study the impacts of top-end heave on the riser undergoing vortex-induced vibration (VIV) are explored in terms of the parametric excitation and the consequent dynamic behaviors. By using finite element simulations based on a coupled hydrodynamic force approach, the dynamic responses of the integrated system including both a floating top-end and the riser experiencing VIV are examined.
Our numerical results show that the riser displacement becomes several times larger than the displacement for the case without top-end motion, and the impact of heave on riser VIV response gets larger as the modal order number dropping. Riser VIV amplitude becomes, almost linearly, more profound when the tension ratio, as one of critical parameters that influence the riser dynamic response, gets larger. Moreover, an interesting phenomenon called mode transition is observed, particularly at lower frequency, during modal dynamics response.
Research on the Coupling Effects Between Ship Motions and Sloshing
Authors: Zhao Wenhua , Yang Jianmin , Tao Longbin , White David 
Published: September 2014

Floating Liquefied Natural Gas (FLNG) facilities, which are a new type of floating platform, have been developed as an alternative to long pipelines for the exploitation of stranded offshore fields. FLNG vessels will be subjected to very complicated and onerous sea states in some regions and very severe motion responses must be avoided. The vessel motion can induce internal tank sloshing, which can in turn affect the global motion response of the vessel. This coupling response is of great importance for the safe design and operation of FLNG facilities in real sea states.
This paper investigates the coupling effect between FLNG roll motions and sloshing. Model tests are carried out for a section of an FLNG vessel containing a tank excited in roll by band-limited white noise waves. During the model tests, the FLNG model is ballasted with fresh water and equivalent steel ballast weights respectively, to quantify the coupling effects due to the internal sloshing. Time histories of the global motions and the internal sloshing oscillations have been measured. Statistical and spectral analyses have been carried out on the measured data. The response amplitude operators are obtained using measured motion spectra divided by the excitation wave spectrum. The influence of the internal sloshing on the global motions has been illustrated through the comparison of the experimental results between the liquid and solid (steel) ballast weight cases. Based on the experimental results, some conclusions regarding the coupling mechanism between FLNG motions and sloshing are drawn.
Prediction of Corrosion Condition Considering Effect of Maintenance
Authors: Yamamoto Norio 
Published: September 2014

Corrosion prediction model which takes an effect of maintenance and repair into account is developed based on the full probability corrosion model. Over-all coating repair, touch-up coating repair and renewing repair of worn member are considered. Change in the corrosion condition due to the maintenance and repair work is modeled and possibility of such change is evaluated.
Based on the developed model, the effects of these maintenance and repair methods to the corrosion condition are numerically examined and discussed. In these numerical examinations, a conventional paint coating and a coating which meets the PSPC (IMO’s Performance Standard for Protective Coatings) specification are examined. Change in corrosion wastage condition due to the maintenance and repair works is evaluated and compared. And the probability that the corrosion wastage exceeds the permissible level is also evaluated.
Symmetric Response of a Hydroelastic Scaled Container Ship Model in Regular and Irregular Waves
Authors: Peng Sheng , Temarel Pandeli , Bennett S. S. , Wu Weiguo , Liu Zhengguo , Wang Yiwen 
Published: September 2014

Wave-induced vibrations, such as whipping and springing, of container carriers have been attracting much attention because of their effects on hull-girder bending moments and fatigue damage. An investigation has been carried out comparing experimental measurements and numerical predictions of symmetric wave-induced loads (i.e. vertical bending moment) of the latest River-sea link container ship design, LPP = 130 m. The dual mission characteristics, namely rivers and open seas, make this type of ship an extremely interesting type of container carrier, particularly in terms of springing and whipping.
A backbone beam segmented model is used in the experiments with the focus on springing- and whipping-induced vertical bending moments, for the model travelling at Fn = 0.21 in regular and long-crested irregular head waves, of 2.5m full-scale height or significant wave height. In addition higher order (harmonics) vertical bending moments (VBM) are also extracted from the experiments. The measurements are taken at amidships and the fore and aft quarters. Numerical predictions, for both the full-scale vessel and segmented model, are obtained using the two-dimensional linear hydroelasticity theories, where the hull structure is idealized as a non-uniform beam and the fluid actions evaluated using strip theory.
The measured model test results, in relatively moderate conditions based on a particular area of operation for this low-draught vessel, indicate that nonlinear springing accounts for a significant portion of the total wave-induced bending moments in regular and, to an extent, irregular waves and slamming effects are small due to the operational area selected. The numerical predictions in regular waves show that linear hydroelasticity analysis can only predict similar trends in the variation of the VBM and the resonance peak. On the other hand, in long crested irregular waves the linear hydroelasticity analysis provides peak statistics that are commensurate with the measurements. The numerical predictions were obtained for two variants, having L = LPP and L = 0.9 LPP, the latter corresponding to the length of the backbone.
Estimation of Weight and Torque on Bit: Assessment of Uncertainties, Correction and Calibration Methods
Authors: Cayeux Eric , Skadsem Hans Joakim 
Published: September 2014

The efficiency of a drilling operation is to a great extent governed by how well one is able to optimize the rate of penetration (ROP) throughout each stage of the operation. ROP optimization normally involves balancing drilling speed on the one hand with acceptable wear to the drill bit on the other. The bit lifetime is largely determined by the mechanical conditions at the bit-formation rock interface and the weight on bit (WOB) and torque on bit (TOB) provide important information related to the working condition of the bit. The accuracy of WOB and TOB measurements can thus become a determining factor for the overall drilling efficiency.
Due to the low bandwidth of downhole mud pulse-based telemetry systems, the WOB and the TOB are generally derived from surface measurements, i.e. from the hook load and the top-drive torque. Field experience indicates that a WOB derived from surface measurements can be of limited accuracy, such as when surface measurements suggest a negative WOB even though the ROP is positive, or when high sampling rate and high precision downhole measurements confirm a large discrepancy between the memory recorded downhole data and the estimated values based on the measurements made at the level of the hoisting equipment and the top-drive.
The reason for these inconsistencies is simply that there are numerous physical processes taking place between the bit and the surface measurements that are normally not accounted for when WOB and TOB are estimated. This paper reviews and analyses the sources of these deviations and models the physical processes in order to quantify the precision for which the WOB and the TOB can be ascertained using solely surface measurements. Methods are also proposed that compensate for certain side effects by utilizing real-time torque and drag and hydraulic calculations.
The Geotechnical Challenges of Tidal Turbine Projects
Authors: Small Andrew A. , Cook Greg K. , Brown Michael J. 
Published: September 2014

Tidal energy projects offer a predictable renewable energy source. Therefore several sites around the coast of the United Kingdom (UK) have been identified to have the potential to host multiple array turbine developments that could be used to generate upwards of 100MW each.
However, the high tidal energy environment required to provide the input to tidal power devices present a combination of design and installation challenges to developers and engineers. Whilst the water depths are comparable to offshore oil and gas projects in the southern North Sea, tidal energy projects present significantly different seabed and associated geotechnical challenges that require novel solutions.
Concerns have been expressed regarding the design of turbine base structures, which is often based upon typical nearshore/offshore soil sampling and geotechnical laboratory testing techniques that are often inappropriate for the seabed materials encountered. This issue is further compounded by the design constraints imposed on the base structure foundations (e.g. tripod gravity base structures). These include strict leveling tolerances required for efficient turbine operation, and which require a detailed understanding of seabed bathymetry at each turbine location where multiple seabed contact points may be required.
In addition to the tidal energy turbines, inter-array cables that connect the turbines and export cable routes which distribute the power to shore also present their own design and installation challenges. It is often overlooked, but significant uncertainty lies in the definition of cable corridors with respect to the seabed materials. In many cases burial may be considered as a means of product protection where seabed conditions allow.
This paper aims to examine the geotechnical issues associated with the difficult seabed and environmental conditions present at typical tidal turbine sites in the UK and globally in an attempt to offer some potential solutions. These issues typically include; difficulties in performing site investigation operations, coarse mobile seabed sediments, challenging seabed topography, exposed bedrock and hard substrates, derivation of appropriate geotechnical parameters, difficulties in foundation design and installation, high cyclic environmental loading, array and export cable lay, on-bottom stability and mechanical protection, amongst others.
Study on the Probabilistic Scenario Based Fire Risk Analysis of FPSO Topside Module
Authors: Jin Yanlin , Jang Beom Seon 
Published: September 2014

Many offshore platforms are normally exposed to the flammable oil & gas circumstances; hence hydrocarbon fire is a big threat to the offshore platform. Fire accidents on the offshore platform usually occupy a major part of the total risks. Nevertheless, existing methods of fire risk analysis used in the industry are still not intact enough to advisably evaluate the risks related to fire accident especially for supporting structures of process modules. For this reason a new procedure of fire risk analysis is established in this paper to overcome those deficiencies in the existing methods. The new method is constructed through a scenario based probabilistic approach.
In the new FRA (Fire Risk Analysis) procedure, the key parameters used for constructing fire scenarios are cautiously considered and discussed in case of causing a conservative judgment. Also, dynamic effect of transient fire accident is properly considered by applying an effective method called ‘snapshot’ during the CFD fire simulation. Furthermore, for investigating the structural failure under the fire, thermal elasto-plastic structural analysis is included in the new FRA.
In the former FRAs, the traditional exceedance curve with certain physical variable is used in the frequency analysis to combine the results of fire simulation and fire frequency calculation. The main purpose of using exceedance curve is for deciding a DAL (Design Accidental Load), which is used for structure design against fire accident or even determining of the proper risk mitigation measures e.g. PFP (Passive Fire Protection). However, different from former FRAs, structure response analysis is carried out in the new procedure and the results are taken into consideration through a newly proposed concept i.e. structural cumulative failure frequency. The purpose of proposing cumulative failure frequency in the new FRA can be summarized as following two aspects. One is to avoid the difficulties of applying the identified DAL to the structure analysis in the former FRAs, and other one is to determine the optimized PFP application area for topside structure. For showing the details of new FRA procedure a demo is also demonstrated in this paper.
The Floatel Superior Loose-Anchor Incident and its Significance for Design and Operation of Semi-Submersibles
Authors: Andersen Terje Leenhart , Kvitrud Arne , Jensen Jan Erik 
Published: September 2014

The combination of dynamic positioning (DP) and conventional anchoring of semi-submersible platforms in the oil industry has recently lead to a serious incident with large loss potential: the Floatel Superior platform suffered severe damage to its hull from a loose anchor in heavy seas during the night of November 6th–7th, 2012. This paper discusses the root causes leading to the incident. The investigation report from the Petroleum Safety Authority Norway (PSA) concludes that damage leading to the loose anchor had developed over several months, and various warning signs during that period were not heeded. The main reason for the damage was rooted in the combined operation mode where position-keeping by use of DP resulted in large environmental loads on the anchors while they were stowed in their bolsters along the vessel side in rough weather when the installation was at survival draught and operating on DP. The anchors on Floatel Superior had also been exposed to environmental loads in excess of the design capacity during extended transit two years prior to the incident. The incident itself was handled efficiently by the crew and emergency preparedness organizations, with 336 people evacuated by helicopter and the remaining 38 crew members transporting the damaged vessel to shore for repairs.
In this paper, an immediate recommendation for removing anchors from the splash-zone while operating on DP is presented as relevant for other installations with similar class notation. In a longer perspective, the investigation found that both well-established design codes and their application in the actual design had shortcomings which played a role in the cause of events. The vessel design appears to have been performed with a principal focus on sub-units (anchor, winch, bolster, pendant-wire attachment) and to an insufficient extent on the combined system use under which it was to be operated. A long-established method of design for connections of auxiliary structures to the main hull structure also showed shortcomings in the event: the doubler plates or pads used to attach the bolsters to the hull did not function as weak links as intended.
Advantages of Polyester Mooring for Deepwater Floaters
Authors: Xu Lixin , Chen Jieyan 
Published: September 2014

Since first installed at a water depth of 4,660 feet in 1997, polyester mooring systems have now been used on floating platforms in the Gulf of Mexico (GOM), Brazil and other regions. The Mad Dog Spar was the first floating production system (FPS) with permanent deepwater polyester moorings in the GOM. After the Mad Dog Spar, the deepest water depth is 7,800 feet in which a polyester mooring system was installed on the Perdido Spar. The polyester mooring systems have performed favorably, e.g., in the GOM, experiencing hurricanes without incident. The polyester rope in general is more advantageous than steel wire in deeper water due to reduced weight (and tension), high strength, durability (better fatigue and no corrosion), and improved floater global performances (less offset, etc.). Moreover, while a floating production platform is designed to support riser systems, fatigue damage of risers due to Vortex Induced Motions (VIM) of the platform are important design drivers particularly in the GOM. The polyester mooring system has a higher restoring force in horizontal (thus a higher lateral stiffness) in currents resulting in a significantly better fatigue performance (less current bins with VIM lock-in) than the steel mooring system does.
The paper herein presents a comparative study with two kinds of mooring systems (polyester ropes and steel wires) for the same platform. Differences between the polyester and steel mooring systems are evaluated for various aspects, such as the mooring system configuration and performance, installation risks, operations, and impact on hull and riser system design and performance. The results also indicate cost savings for the polyester mooring equipment and the overall production system.
Ultra Long Range DTS (>300km) to Support Deep Offshore and Long Tieback Developments
Authors: Gyger Flavien , Chin Sanghoon , Rochat Etienne , Ravet Fabien , Niklès Marc 
Published: September 2014

The continuous demand for energy supplies leads operators to explore and exploit more remote offshore oil fields characterized by deeper deployments, longer tiebacks and subsea completion. These offshore developments either lie in tropical regions subject to stormy weather or in extreme arctic conditions. They imply new requirements in terms of operational efficiency and predictive maintenance for cost optimization as well as environmental footprint minimization.
Consequently, leak detection and flow assurance are required over distances exceeding hundreds of kilometers. And the increasing trend of building all electric completion and heated flowlines impose the use of equally long high voltage power cables.
Distributed temperature sensing (DTS) is a widely adopted technology for leak detection and localization, for heated flow line monitoring and for power cable thermal rating. Optical fiber cables are installed alongside the structure providing detection with meter accuracy localization and degree thermal variation sensitivity. However, there is currently no commercially available DTS instrument capable of reaching a 100km single span without any means of repeating the signal, let alone longer range. Thus, a 300km pipeline would normally require marinized equipment, which is often not a practical solution.
The Omnisens DITEST, a DTS instrument based on Stimulated Brillouin Scattering (SBS) is intrinsically capable of the longest available sensing length, now reaching a sensing distance of around 70km at once; in addition, it is compatible with optical amplifier technology as found in any submarine network. In the present work, we show that, by combining 5 spans of slightly above 65km and 4 optical repeaters together, it is possible to achieve a total of 330km sensing from a single DITEST. Measurement time over the full distance was typically 100minutes, providing a temperature resolution of typically 1K for a spatial resolution of 3m at the end of the 330km long sensing fiber. Shorter measurement time, more suitable with the application could be achieved using optical coding.
As the optical repeater technology is similar to that of telecommunication, efficient cost reduction could be achieved by sharing the repeaters between the sensing system and the needed communication system. At the end of each sensing span, the sensing cable is connected to the repeater for amplification purposes and then goes back to the pipeline for monitoring the next span. The repeaters themselves are electrically powered by conductors embedded in the communication infrastructure.
A viable and cost effective solution to meet the requirements of subsea long distance leak monitoring is thus demonstrated.
Efficiency of Ice Management for Arctic Offshore Operations
Authors: El Bakkay Badr , Coche Edmond , Riska Kaj 
Published: September 2014

The exploration and production of polar oil and gas fields, which are technologically challenging due to extreme weather conditions, are also constrained by strong environmental issues. Safe and economical activities in such hostile and fragile regions require very insightful engineering. The presence of sea ice is representing a triple challenge: economical, technological and environmental. This makes the Arctic exploration and production activities complex.
Ice Management (IM) is one of the tools that could efficiently assist to develop Arctic reserves. However, for each project that uses IM operations, a preliminary study is required to evaluate the efficiency of these support operations and to estimate the possible extension in the season of operation of a field.
Efficiency of an IM philosophy can be estimated in a global view based on the extension in the operability window. In a more detailed view, it can be assessed taking into account the optimal number of icebreakers, the IM patterns, the available time for eventual disconnection, and the floe size reduction (leading to ice load reduction). For this study, we will focus on the ice floe size and loads reduction.
The most common approach for physical management of sea ice is the one where icebreakers reduce floe size of the drifting ice upstream the floating platform (ref. Moran et al. [1], Coche et al. [2]). This paper describes this philosophy and demonstrates based on real-time simulation that its benefit is limited to mild ice scenarios such as unidirectional ice drift. A more efficient way to manage sea ice is (1) to identify the most hazardous events (e.g. big ridges); (2) prioritize these events; and (3) deal with them starting by the most hazardous one.
Preliminary Structural Design of OCAES Vessel
Authors: Xiao Jinfu , Gabr M. , Rahman M. S. 
Published: September 2014

A vessel for Offshore Compressed Air Energy Storage (OCAES) is being considered as a part of the emerging technology to store intermittently generated energy from offshore renewable sources. The basic idea is to submerge the storage vessel into the ocean at a large water depth, convert the energy into compressed air, store it with using the hydrostatic water pressure to balance the compressed air pressure without requiring the storage vessels to resist high internal air pressure. An additional advantage is that the interface of air and water acts as a piston to maintain the air pressure level.
In this study, a rectangular configuration and a cylindrical configuration are proposed for the OCEAS vessel. Stress controlled analyses are performed for the preliminary design of the OCAES vessel with emphasis on characterization of applied cyclic load induced by the air/water exchange in the inflation/deflation process. The stress distribution and deformation pattern in the OCAES vessel at different loading stages are studied by using the multi-physics FEM program COMSOL. Key parameters including storage volume, geometry of OCAES vessel, and material selection are discussed.