bluuebunny/crossref_metadata_2025 huggingface dataset:
Lightweight Hollow Glass Microspheres Drilling Fluid Flow Through Nozzles
Authors: Kirgil O. , Ozbayoglu E. , Miska S. , Yu M. , Takach N. , Mata C.
Published: October 2017

The objective of this study is to investigate flow behavior and survival ratio of different fluids with Hollow Glass Microspheres (HGM) as they pass through jet nozzles under various flow conditions. Three types of HGM with different compressive strengths (5,000 – 19,000 psi) and specific gravities (0.38 – 0.46) for 10% and 30% volumetric concentrations were tested under 196 – 345 ft/s average fluid velocities from 0.5 – 1.5 inch standoff distances during impact tests using a new High Shear Rate Facility (HSRF). Density measurements before and after each circulation cycle were used for calculating survival ratio of the HGM. Particle size analysis was carried out to see the change in the size distribution of HGM after impact experiments. A scanning electron microscope (SEM) was used to view samples of HGM from before and after impact tests to define breakage behavior. The Hertz Impact Law was used to build a mechanistic model to estimate survival ratio under several assumptions. An empirical equation was developed and compared with experimental results. Breakage type is the result of cyclic fatigue because breakage does not occur in one circulation. Standoff distance, concentration of HGM and velocity of the fluid are strong parameters of the survival ratio function. Size distribution analysis and SEM microphotographs show that larger HGM break first.
Uncertainty Quantification of Riser Fatigue Damage due to VIV Using a Distributed Wake Oscillator Model
Authors: Lim HyeongUk , Manuel Lance , Low Ying Min , Srinil Narakorn
Published: October 2017

This study explores the use of polynomial chaos expansion (PCE) to quantify the uncertainty in accumulated fatigue damage in a top-tensioned riser (TTR) due to vortex-induced vibration (VIV). Time-domain simulations of the response of the selected riser are carried out using a distributed wake oscillator model and fatigue damage is computed using rainflow cycle-counting. The uncertainty in damage prediction that results from variability in parameters involved in the wake oscillator model is the focus of this study. The efficiency and accuracy resulting from use of the PCE model is demonstrated by comparison against Monte Carlo simulations (MCS). Specifically, starting with the use of two random variables (the cylinder maximum amplitude and a ratio of the vortex-shedding frequency to the natural frequency) and then by introducing one other random variable (the current velocity), the propagation of uncertainty from the wake oscillator model inputs to fatigue damage is studied. Numerical studies demonstrate the versatility of the PCE-based approach in such uncertainty quantification applications.
Investigation on the Structure Strength and Stability of Ring Stiffened Cylindrical Shell With Long Compartment and Large Stiffener
Authors: Feng Yan , Li Hui , Li Chenfeng , Ruan Junjie , Zhang Qiyou , Xu Weijun
Published: October 2017

With the increasing status of the sea, the research and manufacture of submersible vessel will be paid more attention. In order to enlarge the submergence depth and utilization efficiency of submersible vessel space, long compartment structures of high strength steels and in various forms are widely adopted. The strength problem of such structure is easy to be guaranteed, while the resulting stability problem is becoming more and more serious. For a ring-stiffened cylindrical shell structure with long compartment, one or two large stiffeners are used on the shell structure to ensure its overall stability. This paper studies the strength and stability of the long compartment cylindrical shell structure, with a special emphasis on the stability problems of overall long compartment structures and large stiffeners. The failure modes and critical load under deep water are analyzed by a theoretical method and also a finite element method. The formula for calculating the large stiffener of submersible vessel structure is derived based on the theory of elastic mechanics, and the defect and deficiency of the formula used in the current design specification is pointed out. The influence of large stiffener position and structure form on the critical pressure of submersible cylindrical shell structure is studied. The results of theoretical analysis and numerical simulation are also compared and discussed.
Ductile Tearing of Welds in Pipe Submitted to Cyclic Loading
Authors: Thibaux Philippe , Cooreman Steven , Carlucci Antonio , Vekeman Johan , Van Minnebruggen Koen , De Waele Wim
Published: October 2017

Flowlines and risers can be submitted to plastic deformation, sometimes cyclically, due to the installation technique, or sometimes due to exceptional events. In this case, a specific evaluation of defect acceptance in the girth weld is necessary. The present study investigates the possibility to predict ductile tearing during installation when the performed fracture mechanics tests are only high triaxiality specimens and that the effective application requires cyclic loading. A classical analysis is performed using DNV RP F108 to determine the acceptable defect size of for the case in which a pipe is submitted to cyclic loading. In the present investigation, tearing resistance was characterized with SENB specimens. An engineering critical assessment (ECA) was performed considering the size of the expected defects and the amount of plastic deformation to which the pipeline would be submitted. A validation of the ECA was performed by segment tests. While the application of ECA based on the fracture tests would predict ductile tearing with the considered defect, the results of segment tests only revealed blunting for the considered plastic deformation. It confirms the effect that in lower constraint conditions (like in segment tests), SENB test results are overly conservative. The tearing phenomenon was then simulated by the finite element method using two different damage models (Gurson-Tvergard-Needlemann and the Bai-Wierzbicki model) and compared to the experimental results. As the deformation at the crack tip is typically very large, one needs to have knowledge about the hardening behavior in the post-necking region. As this behavior cannot be directly deduced from standard measurements, an automatic identification procedure was developed to determine the post-necking flow behavior of the weld metal and the base material transverse to the weld. As reported in the literature, simplified models like Rambord-Osgood are then inadequate and model including two hardening zones is necessary: one for small deformation and one for large deformation. The calibration of the damage models was only performed on the tearing curve obtained from the SENB experiments, and the segment tests were then “blindly” simulated.
Experimental Analysis of Ratcheting Failure Based on the Piezomagnetic Response of X80 Pipeline Steel
Authors: Bao Sheng , Hu Shengnan , Gu Yibin
Published: October 2017

The objective of this research is to explore the correlation between the piezomagnetic response and ratcheting failure behavior under asymmetrical cyclic stressing in X80 pipeline steel. The magnetic field variations from cycle to cycle were recorded simultaneously during the whole-life ratcheting test. Analysis made in the present work shows that the piezomagnetic hysteresis loop evolves systematically with the number of cycles in terms of its shape and position. Corresponding to the three-stage process in the mechanical response, piezomagnetic response can also be divided into three principal stages, but the evolution of magnetic parameter is more complex. Furthermore, the loading branch and unloading branch of the magnetic field-stress hysteresis loop separate gradually from each other during ratcheting failure process, leading to the shape of hysteresis loop changes completely. Therefore, the progressive degradation of the steel under ratcheting can be tracked by following the evolution of the piezomagnetic field. And the shape transition of the hysteresis loop can be regarded as an early warning of the ratcheting failure.
Technology Qualification of Offshore Wind Turbine Supporting Concrete Constructions: Mitigation of Future Catastrophic Incidents via Quantification of Unknown
Authors: Samarakoon S. M. Samindi M. K. , Ratnayake R. M. Chandima
Published: October 2017

Understanding the uncertainty associated with the use of new technology and defining the risk of a particular new technology are crucial in its deployment. A systematic risk-based technology qualification (TQ) process enables technology developers to build confidence and systematically document the performance of new technology. The quantification of risk associated with a particular new technology is fulfilled by analysis, using computer-based models, testing, gathering operational data from the field and developing procedures. The TQ enables the potential unwanted events that could result in catastrophic incidents to be investigated, and it subsequently develops tests or analyses that are specific to the identified threats. A systematic approach to TQ provides the quantitative data necessary for making the business case to deploy the technology. This manuscript illustrates a methodology for the TQ of concrete components in offshore wind turbines. For instance, a typical utility-scale offshore wind turbine tower is made of steel tubes that are significantly efficient; the steel towers become rapidly more expensive beyond a certain height, as it is required meet the dynamic characteristic of the turbine to meet the necessary high level of standards for fatigue performance. Although the concrete towers allow more fabrication flexibility, as the design is less driven by fatigue and the use of concrete allows them to be partially or fully fabricated in the field, it is vital to develop risk based TQ methodology to quantify the unknowns.
Performance Evaluation of Air-Backed Metallic Circular Plates Subjected to Close-In Underwater Explosion
Authors: Chen Ganchao , Cheng Yuansheng , Liu Jun , Zhang Changzai , Zhou Tianyu , Zhang Pan
Published: October 2017

The topic on performance evaluation of air-backed metallic structures subjected to close-in underwater explosion is of interest to protecting construction designers. The focus of performance includes not only the deformation/failure modes but also the energy absorption capability. This paper presented a blast experiment to investigate the blast resistance of circular solid plate. The deformation and failure modes were classified. The energy absorption of the blast-loaded plate was quantified by the response of another plate, which was arranged below the target. Particular attention was paid to discussing the effects of the charge mass and stand-off distance (SoD) on the blast performance. Results showed that the target plates appeared to experience petalling failure in case of contact tests and large inelastic deformation in case of noncontact. The shock waves induced by the blast explosion and the fragments teared from the target plates caused a capping or some permanent deformation on rear plates. Damages and deformations of target and rear plates were strongly correlated with the explosion intensity. As the increase of stand-off distance, the failure mode of target plates transitioned from petalling to large inelastic deformation. Experimental results presented in this paper provided valuable guidance for the following research on sandwich structures.
Wear Performance of the Mooring Chain Used in Floating Wind Turbines
Authors: Gotoh Koji , Murakami Koji , Nakagawa Masataka , Utsunomiya Tomoaki
Published: October 2017

To produce offshore wind power generation plants, deep-sea floating wind turbine facilities are required. Commercial installation of floating wind turbine facilities requires a reduction of the mooring cost. Mooring chain breaks due to progressive wear will lead to enormous damages. Therefore, a quantitative wear evaluation method for mooring chains needs to be established. In this study, an experimental setup was constructed to reproduce the wearing phenomenon in mooring chains due to the motion of the floating body induced by waves, and its usefulness was confirmed. The result of the wear test conducted in this study suggests that the tensile force between links affects the degree of wear. Additionally, numerical simulations were performed using a finite element model with measured wear characteristics of the link material to reproduce the phenomenon of wear between links and confirmed that the wear phenomenon could be represented by numerical simulation.
Demonstration Test for Using Suction Anchor and Polyester Rope in Floating Offshore Wind Turbine
Authors: Utsunomiya Tomoaki , Sekita Kinji , Kita Katsutoshi , Sato Iku
Published: October 2017

In this paper, outline of the demonstration test for using suction anchor and polyester rope in a floating wind mast (that was converted from floating wind turbine) is presented. After marine soil investigations and specimen test for polyester rope, the basic design methodology for mooring line including polyester rope and suction anchor is presented. Considering the marine soil investigation result, the profile of the suction anchor was determined to be somewhat short and wide dimensions. Installation of the suction anchor was successfully made at both the test site and the targeted demonstration site. Here, a newly developed suction pump system was successfully used. Installation of polyester rope was also made successfully. However, we observed discrepancy in the suction pressure during the installation of suction anchor at the demonstration site, although we did not see the discrepancy at the trial test site.
Parametric Sensitivity Study of Submarine Power Cable Design for Marine Renewable Energy Applications
Authors: Thies Philipp R. , Johanning Lars , Dobral Corentin
Published: October 2017

An increasing use of submarine power cables is found in dynamic applications such as floating wind, floating wave and tidal generation technologies. These applications substantially differ from common applications, such as floating oil and gas installations in that they are more dynamic. Power cables that cross the water column, so-called umbilicals will be exposed to considerable extreme and fatigue loads mainly induced by the motion of the device, incident waves and tidal current. The actual loading regimes of dynamic submarine power cables in operation are not well understood for marine renewable energy (MRE) applications due to a lack of field experience. The cable design has to consider a combination of cable geometry, hydrodynamic parameters, suitable layout configuration, suitable ancillary systems (e.g. bend stiffeners) in relation to the environmental site conditions.

This paper evaluates the influence of the environmental conditions and the cable design parameters on the mechanical loads and potential failure modes of a dynamic submarine power cable attached to a dynamic floating body in form of a generic point absorber. One notable result is the large effect of the tidal direction, even in relatively moderate flow conditions. The full range of tidal flow conditions should be considered in the power cable design to ensure that the cable MBR is not exceeded in any conditions. The shown configurations also give some insight into the possible variations of the geometric cable configuration. A well balanced S-curve shape yields some of the best results and achieves a good load distribution along the cable and the transition points, whilst avoiding cable compression. The design challenge for the cable configuration is to maintain the S-shape for as many environmental and device response modes as possible in order to achieve high reliability. This paper will be useful for cable, device and site developers of floating MRE to inform the selection of the most suitable cable design.
A New Class of Wave Energy Converter: The Floating Pendulum Dynamic Vibration Absorber
Authors: Marcollo Hayden , Gumley Jonathan , Sincock Paul , Boustead Nicholas , Eassom Adrian , Beck Genevieve , Potts Andrew E.
Published: October 2017

A new class of Wave Energy Converter (WEC) is presented — the Floating Pendulum Dynamic Vibration Absorber (FPDVA). This concept offers significant design benefits to other WEC technology in the form of low cost installation and mechanical moving components located above the waterline only. The key elements of the FPDVA concept are highlighted. The performance of the concept is demonstrated through numerical modeling with calibration of the numerical models via physical tank testing. The Power Take Off (PTO) system is described, and the bench tests are presented. A discussion about the control systems required to operate the FPDVA system and the likely floating body mooring configurations are also presented. The technology has patent pending status. Future phased development of the technology is planned to progress its Technology Readiness Level (TRL) status from TRL 4 to TRL 9.
Investigation of Suspended Particles Around an Obstacle in Vertical Pipe Flow: Comparison Study Experimental and Simulation
Authors: Khatibi Milad , Time Rune Wiggo , Busch Alexander , Johansen Stein Tore , Martins Dwayne Werner , Islam Md. Aminul , Iversen Fionn
Published: October 2017

Particle dynamics within Newtonian and viscoelastic shear thinning flows were investigated with a self-confined cloud of particles around an obstacle. Water and three aqueous Poly-Anionic Cellulose (PAC) solutions were test fluids. An experimental study of an upward vertical pipe was carried out using particle image velocimetry (PIV) techniques to measure the particle and liquid velocity profiles. The fluidized cloud height was measured for better assessing rheological and particle loading effects on particle interactions within liquid flows. It was observed that the dynamics of particles were closely associated with local shear rate, fluid rheology and particle loading. Additionally, it was noted that the slip velocity of particles was relative to the surrounding liquid and was high in regions with a high shear rate and depended significantly on the liquid rheological parameters. The experimental findings were compared against three-dimensional numerical CFD simulations. In the case of particle dynamics in the water sample, it was noted that the simulation results were comparable to the experimental observations. However, for PAC solutions, particles were completely flushed out from the computational domain. This was considered a consequence of inadequate drag and settling velocity formulation within the CFD model. These shortcomings of the drag model were rendered, as Newtonian drag laws were applied to a non-Newtonian fluid, and only used background shear rates of the fluid flow field in estimating the local viscosity experienced by these particles.
Physics-Based Gearbox Failure Model for Multi-MW Offshore Wind Turbines
Authors: Sepulveda Marco , Shek Jonathan , Thies Philipp R. , Oterkus Erkan , Davies Peter , Spring Mark
Published: October 2017

This study proposes an analytical methodology to assess the risk to the operation of an offshore wind turbine in order to identify critical assemblies. The gearbox is one of the critical assemblies regarding maintenance costs and downtime. Failure investigation shows that the high speed shaft bearings are one of the gearbox components with a higher probability of fatigue damage. A physics-based model is developed to calculate the accumulated damage and to estimate the remaining useful life. The model is created for a 3 stage gearbox with two planetary and one parallel helical gear.

This paper summarises the methodology and results of a damage accumulation calculation under a load spectrum derived from 1 year of SCADA data. The final results are consistent with the damage levels found in the failure investigation.
Prediction of Oceanic Rogue Waves Through Tracking Energy Fluxes
Authors: Guo Qiuchen , Alam Mohammad-Reza
Published: October 2017

Here, we show that location of an upcoming rogue wave can be inferred, well in advance, from spatial distribution of energy flux across the ocean surface. We use a statistical approach, and by investigating hundreds of numerical rogue wave realizations in weakly nonlinear wave fields establish a quantitative metric via which predictions can be made. Direct simulations are performed by a higher-order spectral method (HOS), and JONSWAP distribution is used to initialize the wave field. The presented metric may establish a readily achievable measure to identify turbulent locations within a sea, through which timely preventive measures can be taken to minimize damages to lives and properties.
An Integrated Data Management Approach for Offshore Wind Turbine Failure Root Cause Analysis
Authors: Koltsidopoulos Papatzimos Alexios , Dawood Tariq , Thies Philipp R.
Published: October 2017

A significant amount of operation and maintenance (O&M) data are being generated daily from offshore wind farms, including a variety of monitoring systems, maintenance reports and environmental sources. The challenge with having a wide variety of data sources with different temporal and format characteristics, is that a significant effort is required to identify evidence that supports a root cause analysis (RCA) of a turbine fault. In addition, the organization of the O&M data flow does not lend itself to support easy reporting of the O&M key performance indicators. Since the offshore wind industry is growing rapidly, there is a need to better understand and manage the O&M data generated. This paper demonstrates a novel integrated data management system that combines all the O&M data from an offshore wind farm and proves that the proposed RCA framework, based on this integrated platform, can lower O&M costs, by reducing the number of visits to the turbines. It also provides failure rates for subassemblies and looks at the failure distribution within the wind farm. The results of the paper will be of interest to offshore wind farm developers and operators to streamline and optimize O&M planning and activities for their assets.
Prediction of Characteristics of Wave Breaking in Shallow Water Using Neural Network Techniques
Authors: Kouvaras Nicholas , Dhanak Manhar R.
Published: October 2017

The characteristics of wave breaking over a fringing reef are considered using a set of laboratory experiments and the results are used to develop associated predictive models. Various methods are typically used to estimate the characteristics of nearshore wave breaking, mostly based on empirical, analytical and numerical techniques. Deo et al. (2003) used an artificial neural network approach to predict the breaking wave height and breaking depth for waves transforming over a range of simply sloped bottoms. The approach is based on using available representative data to train appropriate neural network models. The Deo et al. (2003) approach is extended here to predict other characteristics of wave breaking, including the type of wave breaking, and the position of breaking over a fringing reef, as well as the associated wave setup, and the rate of dissipation of wave energy, based on observations from a series of laboratory experiments involving monochromatic waves impacting on an idealized reef. Yao et al. (2013) showed that for such geometry, the critical parameter is the ratio of deep-water wave height to the depth of the shallow reef flat downstream of the position of wave breaking, H1/hs, rather than the slope of the reef. H1/hs, and the wave frequency parameter, fH1/g, are provided as inputs to the neural network models of the feed-forward type that are developed to predict the above characteristics of wave breaking. The models are trained using the experimental data. The breaker type classification model has a success rate of over 95%, implying that the neural networks method outperforms previously used criteria for classifying breaker types. The numeric prediction model for the dimensionless position of wave breaking also performs well, with a high degree of correlation between the predicted and actual positions of wave breaking. The performance is higher when only the plunging breaker instances are considered, but lower when only the spilling breaker instances are considered. The corresponding neural network models for wave setup within the surf zone and the difference in energy flux between the incident and broken wave have success rates of approximately 89% and 94% respectively. The method may be extended to provide predictive models for consideration of a range of natural coastal conditions, random waves, and various bottom profiles and complex geometry, based on training and testing of the models using representative field and laboratory observational data, in support of accurate prediction of near-shore wave phenomena.
Validation Study of Smoothed Particle Hydrodynamics in Fluid and Structure Interaction and the Comparison to Boundary Element Method
Authors: Nguyen Nhu , Thiagarajan Krish P. , Cameron Matthew
Published: October 2017

The purpose of this research is to validate the usage of Smoothed Particle Hydrodynamics (SPH) method in solving fluid-structure interaction problems as well as study its advantages and disadvantages compared to another well-known technique Boundary Element Method (BEM). The goal is achieved by 1) evaluating the Response Amplitude Operator (RAO) and 2) analyzing the drifting motion of a 1:10 scaled 3m-discus oceanographic buoy developed by the National Oceanographic and Atmospheric Administration (NOAA), using both experimental and numerical approaches. For the experimental study, the testing was carried out in an 8-m long wave tank and the buoy motions were measured using non-intrusive techniques. For numerical analysis, the project used DualSPHysics — open source code — and ANSYS AQWA — one of the leading software widely used in the marine applications — to simulate all the experimental scenarios via SPH and BEM techniques respectively. It is observed that while BEM has clear advantages in computational time and the ability to study applicable range of frequencies, SPH, in addition to its capability to simulate drifting motion of the floating structure, has shown to outperform the RAO predictions from BEM (especially in low frequency region). In higher frequency regions, the lack of experimental data hinders the conclusion on which method might be more suitable, as both have their own limitations.
Dynamic Response of a Combined Mono-Pile Wind Turbine and Heave-Type Wave Energy Converter System
Authors: Ren Nianxin , Zhu Ying , Ma Zhe , Li Wei
Published: October 2017

In present work, a novel concept by combing a monopile wind turbine and a heave-type wave energy converter has been proposed, that is referred as the ‘MWWC’ (Mono-WT-WEC Combination) system herein. Concept feasibility study has been carried out by doing coupled aerodynamic and hydrodynamic numerical simulation in the time domain. Aerodynamic loads and output wind power of the NREL 5MW wind turbine are determined by the NREL Aerodyn code, based on BEM method. Hydrodynamic loads of the mono-pile and the WEC are calculated by the AQWA code, which is available for modeling multi-body systems including both mechanical and hydrodynamic couplings between the mono-pile and the WEC. Firstly, the effect of different power-take-off (PTO) parameters and wave periods on the performance of the WEC’s wave energy production under typical wave cases has been investigate, and a preliminary optimal value for the PTO’s damping stiffness has been proposed; secondly, the dynamic characteristic of the MWWC system has been investigate using coupled wind-wave loads analysis under typical operational sea cases. Finally, the extreme responses of the MWWC system have been obtained for its ULS design, and the potential challenging areas of the MWWC system has been highlighted.
Revision of DNV GL Design Standard for Floating Wind Turbine Structures
Authors: Hopstad Anne Lene Haukanes , Ronold Knut O. , Argyriadis Kimon
Published: October 2017

The first edition of the DNV Offshore Standard “Design of Floating Wind Turbine Structures”, DNV-OS-J103, was published in June 2013. The standard represented a condensation of all relevant requirements for floaters in existing DNV standards for the offshore oil and gas industry which were considered relevant also for offshore floating structures for support of wind turbines, supplemented by necessary adaptation to the wind turbine application.

As part of the harmonization of the DNV GL codes for the wind turbine industry after the merger between Det Norske Veritas (DNV) and Germanischer Lloyd (GL) in the autumn of 2013, DNV GL currently plans to publish a revision of DNV-OS-J103 in 2017, to become identified as DNVGL-ST-0119.

The new revision is intended to reflect the experience gained since 2013 as well as the current trends within the industry.
Frequency Domain Analysis of the Interactions Between Multiple Ships With Nonzero Speed in Waves or Current-Wave Interactions
Authors: Liu Yujie , Falzarano Jeffrey M.
Published: October 2017

We study the multi-body problems with a nonzero speed or with current-wave interactions using the Green function method. The two problems are equivalent when the current is along the longitudinal direction of the ship.

The formulations of a single ship for the zero-speed and nonzero-speed cases are derived. The concepts, the motivations and the assumptions are explained. We also provide the derivations of the added mass and damping for the asymmetric ship profile. Then we extend the conclusions to the multiple ships and formulate the multi-body problems. The in-house program MDL Multi DYN is validated through the study of two Wigley hulls with zero speed in waves. After that, the results for two moving Wigley hulls are generated. The two ships are assumed to advance in parallel at the same speed. Finally, the effects of the separation distances and the different speeds are discussed.
Numerical Simulation of Motion of Rotating Drill Pipe due to Magnus Effect in Riserless Drilling
Authors: Inoue Tomoya , Suzuki Hiroyoshi , Tar Thaw , Senga Hidetaka , Wada Kazuyasu , Matsuo Miki Y.
Published: October 2017

During riserless drilling operations, which are carried out in some scientific drillings and in the initial stages of all drilling operations in oil and gas exploration, a lifting force is generated in addition to a drag forces in ocean current environment owing to the ocean current and the rotation of the drill pipe. This is called the Magnus effect, and it is a critical phenomenon during such operations.

First, the lifting and drag forces are calculated using the computational fluid dynamic (CFD), and the lift and drag coefficients are calculated for several rotational velocities of the drill pipe and the velocities of the ocean current. It can be observed through the calculations that the lifting force increases as the rotational velocity of the drill pipe increases, and it reaches a level of approximately several times that of the drag force. The force reaches such a considerably high magnitude that it can induce the motions of the drill pipe, resulting in the generation of a high bending moment.

An analytical model of a drill pipe has been established by applying an absolute nodal coordinate formulation (ANCF), which can express a relatively flexible and long pipe, such as a drill pipe. ANCF is a finite element method, and was basically developed to analyze deformable linear objects such as the cable. With ANCF, the absolute slopes of elements are defined based on the absolute nodal coordinate. Finally, the drill pipe motions are simulated using the established model by applying the results of CFD simulations for sample cases and referencing the operation of the Chikyu.
Applicability of Geopolymer Materials for Well P&A Applications
Authors: Salehi Saeed
Published: October 2017

Previous research on application of geopolymers in oil/gas wells is mainly unsuccessful due to failure to achieve a reasonable thickening time. This study presents geopolymer composite mixtures that have high compressive and shear bond strength, enhanceed thickening time, high durability, and reasonable shrinkage. Class F fly ash geopolymers are used for developing samples with different mix designs in this work. Class H Portland cement is used as a controller on all the tests conducted in this work. Tests conducted in this research include: unconfined compressive strength (UCS), shear bond strength, thickening time, and durability tests. Results indicate temperature as a crucial factor affecting the thickening time of geopolymer mix slurry. More than four hours thickening time is achieved by optimizing mix design and applying a developed mix of superplasticizer and retarder. UCS testing indicates a high compressive strength after one and fourteen days of curing for geopolymer mixtures. More than 6000 psi strength is achieved in long term (28 days curing). This indicates strength gained over time, for geopolymer mixture, where strength retrogression effects are observed for Portland cements. Results also reveal higher shear bond strength for Geopolymer mix, which can better tolerate de-bonding issues. Additionally, more ductile material behavior and higher fracture toughness, were observed for optimum geopolymer mixes. Final observations confirm applicability of these materials for oil and gas well cementing with circulating temperatures up to 300°F.
Influence of Offshore Reefs on Low-Frequency Waves During Harbor Resonance
Authors: Gao Junliang , Ji Chunyan , Ma Xiaojian
Published: October 2017

In this paper, a fully nonlinear Boussinesq model is used to simulate the shoreward propagation of bichromatic wave groups over different fringing reef topographies and the subsequent low-frequency oscillations inside a harbor. Based on a low-frequency wave separation technique, the effects of the reef-face slope and the reef ridge on the bound and free long waves inside the harbor and their relative components under the condition of the lowest resonant mode are systematically investigated. For the given harbor, the given reef ridge and the range of the incident short wave amplitudes and the reef-face slopes studied in this paper, results show that the amplitude of the free long waves inside the harbor increases with the reefface slope, while the bound long waves inside the harbor is insensitive to the variation of the reef-face slope. The existence of the reef ridge can notably restrain the bound long waves inside the harbor when the incident short wave amplitudes are large, while it has little influence on the free long waves inside the harbor.
Time Scale of Scour Below Submarine Pipeline Under Combined Waves and Currents With Oblique Incident Angle
Authors: Zang Zhipeng , Tang Guoqiang , Cheng Liang
Published: October 2017

Available formulae for the time scale of scour below a submarine pipeline are so far mainly restricted to waves-only and currents-only conditions with normal incidence and no burial of the pipeline. This paper presents experimental results on temporal and spatial developments of local scour below a partially buried pipeline under combined waves and currents with oblique incident angle. There are also some tests with waves-only and current-only conditions for validation purpose. All tests were conducted under live-bed conditions. The maximum Shields parameter is used to formulate the nondimensional time scale of local scour under combined waves and current conditions. The effects of flow incident angle and embedment depth on the time scale of scour were investigated. The results show that the time scale increases with the increase of incident angle and also increases with the increase of the embedment depth for combined waves and current conditions. The effective shields parameter is applied to account for the effect of the oblique incident angle based on the fact that both the normal component and the axial components of the flow contribute to the scour process when the currents or waves approach the pipeline with an oblique angle. It is found that the previously proposed empirical formula for time scale of scour for waves-only and current-only conditions, is also applicable to the combined waves and current conditions, if the maximum Shields parameter is used as the governed parameter in quantifying the time scale.
A Novel Approach for Selecting Main Dimensions of New Sandglass-Type FPSO
Authors: Du Yazhen , Wang Wenhua , Wang Linlin , Huang Yi
Published: October 2017

In order to fully exploit the potential of FPSOs in the development of offshore oil field, a new concept of sandglass-type FPSO has been put forward recently. In this paper, a novel approach is proposed for designing the main dimensions of the new sandglass-type floating body. With the application of the strip method, the wave-free frequency in heave motion is intensively investigated. The resulting expression shows that the wave-free frequency has close connection with the water-plane area and the corresponding added mass. Then a uniform approximation of the relationship between the added mass and the main dimensions of structure below the waterline is discussed. By comparing with the numerical results of minimum heave RAO of heave motion, the validity and rationality of the proposed method are verified. Besides, experiments are carried out for the sandglass-type floating model and the results support the numerical results and the proposed method. Finally, combining with other requirements in the configuration of the structure above the waterline for the operation at sea, the design scheme for the main dimensions of the sandglass-type FPSO is established.
Oil Country Tubular Goods Fatigue Testing: Do We Test Them Enough?
Authors: Teodoriu Catalin
Published: October 2017

Fatigue is the most common known problem of drill pipes, since the combination of make-ups performed to connect the pipes and all the external loads, together with the threaded geometry of the connections, will stimulate the appearance of high stress points, cracks and finally promoting considerable economic losses. When threaded connections are used to connect the casing string, the fatigue resistance of the connection will affect the whole integrity of the string, and thus, in most cases, it is lower as the casing body. Generally, fatigue is classified as low-cycle fatigue and multi- or high-cycle fatigue. For Oil Country Tubular Goods (OCTG), a typical high cycle fatigue is represented by drill pipe fatigue in deviated wells. Unlike drill pipe, the casing may be exposed both to low-cycle as well as to high-cycle fatigue. Low-cycle fatigue is a common type of failure when the applied loads induce high stresses in the metallic material. The number of cycles may vary from as low as 10 up to 100. High-cycle fatigue requires a large number of cycles to failure. In order to avoid catastrophic failures, high-cycle fatigue resistance is usually considered to be sufficient if the number of cycles is above 106. The oil business has focused excessively on testing drilling risers and drill pipes under fatigue loads, but when it comes to casing and tubing the experimental approach may require different solutions. Drilling with casing opened the intensive testing of casing connections against fatigue resistance. Moreover, recent papers have shown intensive work on redesigning connections to withstand fatigue. New applications like rotating while running require a rethinking of testing strategy of Casing and Tubing. The following paper focuses on answering the question whether we test enough. The first part compares existing testing facilities, followed by an intensive discussion about the true loads of a casing or tubing connection. Using public testing data, the second part of the paper tries to identify how far the results provided by various types of testing machines can be compared with each other. For example, we found that low cycle fatigue results may not fully reflect the predictions based on extrapolations of high cycle fatigue results.
Experimental Study of Liquid-Liquid Flow Through Upward Vertical to Horizontal Transition
Authors: Mazza Ricardo A. , Suguimoto Fábio K.
Published: October 2017

This work consists of an experimental analysis of the liquid-liquid two-phase flow of water-kerosene through a vertical bend. The duct has diameter of 0.026 m, the bend radius is 0.125 m and the superficial velocities of the water and kerosene ranged from 0.1 to 1.0 m/s. The pressures drops were measured by differential pressure transducers SMAR LD301, the holdups were determined by the method of trapping fluid using quick-closing valves and the flow patterns was determined using a high-speed camera. The bend pressure gradient is increased with the superficial velocities of both phases. The bend coefficient has no correlation with the mixture Reynolds number, such as in single-flows. The modified Reynolds number proposed by [1] described accurately the bend flow pattern.
A Numerical Model for Submarine Pipelines With Concrete Coating
Authors: Nguyen Ngoc , Fyrileiv Olav , Chia Chor Yew
Published: October 2017

This paper presents a numerical model that is used to estimate the structural response of a submarine pipeline with concrete weight coating subjected to loadings commonly encountered in pipeline installation and operation phases. Findings from parametric studies performed with the numerical model are used to widen the applicable range of the simplified concrete crushing criterion in DNV-OS-F101 (2013) and formulate a rational approach for the design of pipeline concrete weight coating under typical installation and operation conditions. The rational design approach will allow for potential selection from a wider range of installation vessels and relaxation of the installation weather window criterion. The design method also provides insights into the strain concentration in the field joint at different strain levels, which is used to assess the field joint welding integrity for pipeline in free spans and in high strain conditions.

The numerical model considers nonlinearities in steel and concrete material stress and strain, as well as complex adhesive behaviour of the anti-corrosion coating. Good agreement is obtained between the numerical results and existing experimental data for all the sections along the pipeline model where comparisons are made on moment–strain global behaviour, sliding from the concrete coating, hot spot strain near the field joint and concrete strain.

The numerical program is performed within the scope of Phase 1 of the joint industry project called “Design of concrete coating for submarine pipelines”. Laboratory tests to check and improve the numerical model are planned for Phase 2.
Autonomous Tool for Downhole Water Production Management
Authors: Voll Benn , Aadnøy Bernt S.
Published: October 2017

A new tool to stop, control and manage water production in oil wells is presented. The tool is simple and robust and can be installed blindly with no concern for orientation. The tool is fully autonomous and does not require external signal or power. The water stop tool has a high potential for effective reservoir management as it can stop water locally, reopen if oil again enters the tool, and also reroute water to surface or to a water bearing formation through a separate conduit.
Hydrodynamic Response of Three Column Semi-Submersible Floater Supporting Vertical Axis Wind Turbine
Authors: Krishnan Rajeswari , Seeninaidu Nallayarasu
Published: October 2017

Offshore wind energy extraction has gathered momentum around the world due to its advantages over onshore wind farms at various fronts. The floating support system with vertical axis wind turbine might prove to be feasible concept in medium to deep waters. In this context, this paper addresses an investigation of hydrodynamic analysis of three column semi-submersible with Vertical Axis Wind Turbine (VAWT) in parked condition under regular and random waves. Free decay experiments were conducted for using scale model (1:75) in a laboratory wave basin at the Department of Ocean Engineering in Indian Institute of Technology Madras, India. Computational Fluid Dynamics (CFD) simulations were used to assess damping characteristics and validated with the experiments. Numerical simulations of hydrodynamic motion response of the floater were carried out using potential flow theory based commercial software (ANSYS AQWA). The damping values obtained from experiments were used in numerical simulations to obtain motion response and Response Amplitude Operator (RAO). The motion response obtained from the study was used to verify the suitability of the system for deployment in east and west coast of India.
Effect of Microblock on the Compressive Strength of Portland Cement at Elevated Temperatures
Authors: Gaurina-Međimurec Nediljka , Sedić Krunoslav , Čajić Anel , Matijević Ante
Published: October 2017

Cementation of casing string depends on composition and properties of cement slurry. The properties of Portland cements must often be modified to meet the demands of a particular well application. These modifications are accomplished by the admixing of additives that effectively alter the hydration chemistry. Silica (SiO2) is used most frequently for the prevention of strength retrogression. It can have a different particle size (“silica sand”, with an average particle size of about 100 μm; “silica flour”, with an average particle size of about 15 μm; and “silica fume”, with mean particle size between 0,1 μm and 0,2 μm). Commercially available additive “Microblock” was used in lab tests. It is a liquid cement additive made from a finely divided, high surface-area silica (D50: cca 0.15 μm; D90: cca 0.75 μm). “Microblock” can help prevent high-temperature strength retrogression, control lost circulation as well as gas migration and can provide a degree of fluid-loss control. The Portland cement slurries with 10%, 20%, 30% and 40% of “Microblock” have been tested. Results of laboratory tests have shown that silica fume (also known as microsilica) affects the slurry properties such as thickening time, rheology, fluid loss, free water, slurry stability, and set cement compressive strength. The development of high early compressive strength is important to ensure structural support to casing and hydraulic/mechanical isolation of downhole intervals. The development of compressive strength of Portland cement slurries with and without “Microblock” at different curing temperature (90 °C, 120 °C and 150 °C) has been determined by Ultrasonic cement analyzer. Results have shown that “Microblock” affects the properties of cement slurry and set cement. The compressive strength has been higher with the addition of “Microblock” than compressive strength of neat PC slurry, but negative effect has been exhibited on slurry rheology and early strength development at elevated temperatures.
Using Discrete Element Model to Simulate Keel-Gouging: A Sensitivity Analysis
Authors: Bailey Dudley Eleanor , Liu Lei , Sarracino Robert , Taylor Rocky
Published: October 2017

A three-dimensional discrete element model is under development to simulate a number of different keel-gouge and subsea interaction scenarios. The model is being validated against controlled tests conducted in the National Research Council’s ice tank facility under the Pipeline Ice Risk and Mitigation (PIRAM) Joint Industry Project, which was led by C-CORE on behalf of a number of oil and gas companies. To investigate the influence of certain key parameters on the failure behaviour of the keel, a sensitivity analysis has been carried out. Best results were achieved when Young’s modulus of the keel was 5 MPa, the shear-to-tensile ratio of the freeze bonds was set to 1.2, the internal friction angle of the ice was 9°, the bond breakage ratio 0.8 % and Young’s modulus of the gravel 0.01 MPa. A low modulus for the gravel was needed to prevent premature failure of the keel, a consequence of the model not accounting for soil deformations. Using these parameters the model was able to accurately reproduce the loads on the soil tray during peak loading. Future developments in the model include using ‘clumps’ to give more representative ice block shapes, which will allow interlocking between ice pieces and the development of force chains.