bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vortex Induced Vibrations and Fatigue Assessment of Pipe-in-Pipe Systems
Authors: Yang Zhengmao , Thorkildsen Fartein , Norland Kristian 
Published: September 2018

The high thermal insulation potential of a pipe-in-pipe system makes it the preferred solution for challenging flow assurance conditions. Due to the higher bending stiffness of a pipe-in-pipe system, longer free spans would be expected for pipelines resting on uneven seabed. However, there are no clearly defined standard formulae for the calculation of structural response of free spanning pipe-in-pipe system exposed to vortex induced vibration (VIV) and the resulting fatigue damage. If the same method as for a single wall pipe was applied, the combined equivalent pipe properties would be assumed and the VIV response and stresses of the equivalent pipe could be obtained. However, the longitudinal stresses in the inner and outer pipe to be used for the fatigue assessment of the girth welds would not be easily obtained, especially for sliding pipe-in-pipe systems.
Based on previous experience and development work for pipe-in-pipe systems, a numerical model for VIV assessment of sliding pipe-in-pipe systems is proposed giving improved interpretation of individual pipe characteristics. Modal analyses of sliding pipe-in-pipe systems are performed by using this numerical model. The natural frequencies and mode shapes are extracted. According to the numerical analysis results, the longitudinal stress ranges due to VIV are obtained and fatigue assessment of the pipeline girth welds for the inner and outer pipes are performed. In order to understand the interaction between the outer and inner pipe, the effect of friction and initial gap between the centralizers and outer pipe surface are studied.
A Study on the Dynamic Ultimate Strength of Global Hull Girder of Container Ships Subjected to Hogging Moment
Authors: Yamada Yasuhira , Kameya Kyoko 
Published: September 2018

The purpose of the present study is to investigate dynamic ultimate strength of global hull girder of container ships using large scale non-linear finite element analysis. A series of time domain non-linear FE-simulation is carried out using large scale FE models of a 8000 TEU container ship where a hogging moment is applied to the midship section. 5 types of finite element models (three full models, a half hold model, a 1 transverse model) are used. These models adopt elasto-plastic material model which includes strain rate effect.
The hogging moment which is modeled by sinusoidal impulse is applied to these models, and collapse mechanism as well as dynamic hull girder ultimate strength is investigated by varying the load time duration. Moreover effects of load time duration, mass inertia, strain rate and analysis models are investigated in detail. It is found from the present study that ultimate strength as well as collapse mode are significantly dependent on load time duration of hogging moment.
Strouhal Number for VIV Excitation of Long Slender Structures
Authors: Potts Andrew E. , Potts Douglas A. , Marcollo Hayden , Jayasinghe Kanishka 
Published: September 2018

The prediction of Vortex-Induced Vibration (VIV) of cylinders under fluid flow conditions depends upon the eddy shedding frequency, conventionally described by the Strouhal Number. The most commonly cited relationship between Strouhal Number and Reynolds Number for circular cylinders was developed by Lienhard [1], whereby the Strouhal Number exhibits a consistent narrow band of about 0.2 (conventional across the sub-critical Re range), with a pronounced hump peaking at about 0.5 within the critical flow regime. The source data underlying this relationship is re-examined, wherein it was found to be predominantly associated with eddy shedding frequency about fixed or stationary cylinders. The pronounced hump appears to be an artefact of the measurement techniques employed by various investigators to detect eddy-shedding frequency in the wake of the cylinder.
A variety of contemporary test data for elastically mounted cylinders, with freedom to oscillate under one degree of freedom (i.e. cross flow) and two degrees of freedom (i.e. cross flow and in-line) were evaluated and compared against the conventional Strouhal Number relationship. It is well established for VIV that the eddy shedding frequency will synchronise with the near resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal Numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under one degree of freedom exhibit a mean Strouhal Number of 0.2 consistent with fixed/stationary cylinders, cylinders with two degrees of freedom exhibit a much lower mean Strouhal Number of around 0.14–0.15.
Data supports the relationship that Strouhal Number does slightly diminish with increasing Reynolds Number. For oscillating cylinders, the bandwidth about the mean Strouhal Number value appears to remain largely consistent. For many practical structures in the marine environment subject to VIV excitation, such as long span, slender risers, mooring lines, pipeline spans, towed array sonar strings, and alike, the long flexible cylinders will respond in two degrees of freedom, where the identified difference in Strouhal Number is a significant aspect to be accounted for in the modelling of its dynamic behaviour.
Dynamic Response Analysis on the Interaction Between Flexible Bodies of Large-Sized Wind Turbine Under Random Wind Loads
Authors: Li Yilun , Guo Shuangxi , Li Min , Chen Weimin , Kong Yue 
Published: September 2018

As the output power of wind turbine increasingly gets larger, the structural flexibility of elastic bodies, such as rotor blades and tower, gets more significant owing to larger structural size. In that case, the dynamic interaction between these flexible bodies become more profound and may significantly impact the dynamic response of the whole wind turbine. In this study, the integrated model of a 5-MW wind turbine is developed based on the finite element simulations so as to carry out dynamic response analysis under random wind load, in terms of both time history and frequency spectrum, considering the interactions between the flexible bodies. And, the load evolution along its transmitting route and mechanical energy distribution during the dynamic response are examined. And, the influence of the stiffness and motion of the supporting tower on the integrated system is discussed.
The basic dynamic characteristics and responses of 3 models, i.e. the integrated wind turbine model, a simplified turbine model (blades, hub and nacelle are simplified as lumped masses) and a rigid supported blade, are examined, and their results are compared in both time and frequency domains. Based on our numerical simulations, the dynamic coupling mechanism are explained in terms of the load transmission and energy consumption. It is found that the dynamic interaction between flexible bodies is profound for wind turbine with large structural size, e.g. the load and displacement of the tower top gets around 15% larger mainly due to the elastic deformation and dynamic behaviors (called inertial-elastic effect here) of the flexible blade; On the other hand, the elastic deformation may additionally consume around 10% energy (called energy-consuming effect) coming from external wind load and consequently decreases the displacement of the tower. In other words, there is a competition between the energy-consuming effect and inertial-elastic effect of the flexible blade on the overall dynamic response of the wind turbine. And similarly, the displacement of the blade gets up to 20% larger because the elastic-dynamic behaviors of the tower principally provides a elastic and moving support which can significantly change the natural mode shape of the integrated wind turbine and decrease the natural frequency of the rotor blade.
Effects of Correlation Between Waves and Currents on Pipeline Free Span VIV Fatigue: A Case Study
Authors: Besedin Dmitry , Peek Ralf , Ang Sze Yu , Vedeld Knut , Fyrileiv Olav , Gulyaev Alexey 
Published: September 2018

In shallow waters, subsea pipelines can suffer fatigue damage from Vortex Induced Vibrations (VIV) by the combined effects of waves and currents.
A full characterization of the joint probability distribution of waves and currents involves at least 5 variables, 2 for currents (magnitude and direction), and 3 for waves (significant wave height, mean wave direction, and wave period at the peak of the spectrum). In lieu of sufficient data to adequately characterize the associated joint probability density function, DNV GL in their “Recommended Practice” propose an approximation: Assume that the direction of current and wave effects is always the same, but for a given direction, waves and currents are assumed statistically independent.
In this paper 28 years of hindcast data are used to test the accuracy of this colinearity approximation in the Sea of Okhotsk. Rather than attempting to estimate a joint probability density function in 5 variables, the span fatigue assessment is simply performed for the entire 28 years of the hindcast database to obtain an average rate of fatigue damage. It is found that this history-based approach can lead to fatigue damage rates that are much higher than those derived from the colinearity assumption.
This non-conservatism of the colinearity assumption, arises for pipeline orientations for which both waves and currents can contribute strongly to the VIV response without being exactly colinear.
It is concluded that caution is needed in using the colinearity assumption, but an update of the span assessment procedure should also address issues for which current assessment procedures are conservative, such as seabed proximity and trench effects, nonlinearity in the pipe-soil interaction, and the change in axial forces due to transverse displacements of the pipe, which are expected under extreme combined current and wave conditions, as envisioned on on-bottom stability design criteria.
Research on Hydrostatic Stability Calculation Method for Mobile Offshore Units
Authors: Ding Yong , Cao Shunli , Lan Linxin , Chen Mo , Pan Liming 
Published: September 2018

Since most offshore platforms have comparable length and breadth, the transverse stability is not sufficient to estimate safety of floating platform. The current solution is to follow conventional transverse stability methodology to any orientation, then take the weakest one as a key consideration. However, the analysis ignores trim in all process of heeling. Longitudinal balance at each heel angle reduce the righting arm of platform, which is more reasonable.
In this study, the Euler angles are used as floating parameters of platform, and three kinds of longitudinal balance cases are divided. The oblique free trim method and the free twist method, two of the three cases mentioned, are chosen to establish floating equations of platform. The potential energy surface and the longitudinal coefficient of stiffness are applied to the analysis from standpoints of energy balance and moment balance separately, the former is used to get the most critical axis for a given heel angle, and the latter can be used as the stability criterion of floating condition. Following this idea, a numerical tool has been developed.
This paper describes the method used to estimate the stability of offshore platform, and validation work is presented for simple geometries. Then, results from two operational stability studies are discussed. Finally, possible further work is discussed.
Benchmark of Erosion Criteria in a Deepwater Development
Authors: Gómez-Álvarez Susana , García Ruíz Fernando , Merino-García Daniel 
Published: September 2018

Ultra-Deep water projects worldwide and particularly in Brazil are characterized by high capital investment costs. This fact generated the need to explore opportunities to improve project value, even though the project was still during visualization phase.
One of the identified opportunities was related to API 14E erosion standard application, as it is considered to be conservative for estimating the erosional limits in oil and gas applications. There are additional industry practices that are widely used in industry that provide more accurate estimations of erosional velocity limits. If these values are increased, there is an opportunity to enhance project value as it would allow a reduction of the required number of wells and production line / riser diameters. If the API erosional limit is considered in the project, the wells would produce at lower rate than reservoir potential, which would lead to an increase in the number of development wells. Based on the significant perforation cost of deepwater wells, the increase on this number would be reflected in the total development Capex, eroding the project value.
This paper describes the work performed in order to better understand the possible erosion phenomena in the production system due to the high fluid velocities in a gas condensate field and to determine the maximum allowable gas rate with different erosional models (API 14E and Tulsa SPPS).
The proposed methodology provides the opportunity to enhance project value by predicting erosional rate limits via SPPS, as the current applied standard was considered to be conservative in erosional rate prediction. If confirmed as feasible, significant cost reduction could be achieved in the project as the individual gas well production could be increased by the reduction of the number of wells; estimated well cost reduction is around 400 MMUSD per well, plus associated subsea production system.
Numerical Integration of the AUSMV Scheme With a Dynamic Wellbore Temperature Model
Authors: Udegbunam John Emeka , Fjelde Kjell Kåre , Sui Dan 
Published: September 2018

The AUSMV scheme is a hybrid transient model derived from Advection-Upwind-Splitting Method (AUSM) and Flux Vector Splitting (FVS) method. The two-phase flow model was formulated under isothermal condition. This neglected the behavior of temperature during transient scenarios, for instance, unloading and drilling fluid circulation. In contrast to this assumption, wellbore temperature changes locally with time under such dynamic conditions.
The numerical accuracy of the AUSMV scheme can be improved in two ways. The scheme can be reformulated by including energy equation in the system of governing conservation laws. This option, however, is computationally rigorous and expensive. A better alternative is to develop a separate dynamic temperature model that will calculate wellbore and formation temperatures. Then the two dynamic models — the AUSMV scheme and temperature model — are numerically coupled into a thermohydraulic simulator.
The present work will include a brief introduction to the AUSMV scheme, followed by the description of the temperature model. In addition, how the two transient models are integrated will be presented.
Simulation cases, demonstrating the improved modeling capability of the scheme for a drilling situation, will be shown.
Experimental and CFD Study of Circulation Efficiency in Simulated Irregular Annulus
Authors: Divyankar Shreyansh , Khatibi Milad , Time Rune Wiggo , Skadsem Hans Joakim , Aasen Jan Aage 
Published: September 2018

Primary cementing is a critical well construction operation that should ensure annular zonal isolation over the life cycle of the oil well. Efficient conditioning and mobilisation of mud prior to cementing is important to ensure that residual mud, especially in washout zones, does not contaminate the cement slurry. Therefore, experiments are carried out to better understand the flow dynamics and associated phenomenon in irregular geometry.
The narrow annulus between casing and formation is approximated by a rectangular slot, in order to aid instrumentation and data acquisition purposes. This methodology can be justified to reproduce flow in narrow annuli fairly well, and is considered a very useful technique for measurement in narrow geometries.
Particle image velocimetry (PIV) is used to obtain the liquid velocity profiles in regular and irregular sections of the experimental setup. Analysis of velocity profiles and vector fields provides information on regions of flow in the vicinity of the irregularity, and this allows a systematic study on the effects of flow rate in regular and irregular wellbore geometries. Entry effects from regular to irregular section and the development of areas with recirculation zones are investigated in irregular section. This enables us to estimate variability of circulation efficiencies in the irregularity. The experimental results are compared with numerical simulations in corresponding irregular geometry.
Effect of Buoyancy and Inertia on Viscoplastic Fluid: Fluid Displacement in an Inclined Eccentric Annulus With an Irregular Section
Authors: Kragset Steinar , Skadsem Hans Joakim 
Published: September 2018

Primary cementing is an important well construction process that should establish well control barriers and zonal isolation. Critical for primary cementing is the successful displacement of drilling fluid from the annulus between casing and formation by a sequence of spacer fluids and cement slurry. Failure to displace the drilling fluid may compromise the annular cement integrity and result in contaminated cement with degraded mechanical properties. Issues such as eccentricity, washouts and other geometric irregularities in the wellbore can complicate the displacement processes, and their effect on the quality of the cementing job and the final result is linked to uncertainty.
We present numerical simulations of the displacement process between two viscoplastic fluids in the vicinity of a symmetric local hole enlargement. The study is limited to laminar flow regimes in the regular part of the annulus, and we focus on a near-horizontal section with significant eccentricity and small annular clearance. We vary the volumetric flow rate and the mass density difference between the fluids, and study how the irregularity affects the displacement efficiency and the presence of residual fluid in and after the irregularity.
In the regular part of the geometry, eccentricity favors flow in the wider, upper part of the annulus, while density difference leads to azimuthal flow from the top to the low side of the annulus. The results support the assumption that increasing the mass density difference improves the displacement efficiency. In the laminar regime, lower flow rates can be favorable over higher ones in terms of efficiency measured as a function of volume that is pumped into the enlarged section.
Displacement of drilling fluids for primary cementing is a rich flow problem involving different non-Newtonian fluids and possibly irregular geometry. Simulations of the displacement process can aid in optimizing fluid properties and injection rates for primary cementing operations, and assist cement log interpretation after the operation.
Considerations in Design of Centralizers for Pipe-in-Pipe Systems
Authors: Manouchehri Soheil 
Published: September 2018

For un-bonded (sliding) Pipe-In-Pipe (PIP) systems, one of the main components is the centralizers (also called spacers). The main functions of the centralizers are to centralize the inner pipe inside the outer pipe, to transfer the loads between inner pipe and outer pipe and to safeguard the insulation material in the annulus from excessive compression during fabrication, installation and operation.
Centralizers must also have good thermal insulation properties so that the heat loss is minimized. Different designs are now available for centralizers but the majority are based on two half shells which are bolted together. During fabrication, installation and operation, centralizers subject to different loads under which they are required to continue functioning properly.
This paper provides an overview of centralizer design aspects and then focuses on the loading history during installation using reeling method. The main contributing parameters to centralizer loading during reeled installation technique are discussed and conclusions are drawn. It is believed that this will enable Pipeline Engineers to select the most appropriate material and design for centralizers.
Experimental and Numerical Evaluation of Manoeuvring Capability of an AHTS Using Free-Running Tests
Authors: Swan de Freitas Caio , Vileti Vinicius L. , Esperança Paulo de Tarso T. , Sphaier Sergio H. 
Published: September 2018

Investigating the hydrodynamics of a ship manoeuvring is a continuing concern for researchers. In recent years, with the growth of the operations complexity, understanding the hydrodynamics of a ship manoeuvring has become a central issue for supply vessels operating in close proximity of oil platforms. One of the main obstacles in understanding this problem is the difficulty of reproducing the manoeuvring on real ships with acceptable measurements, uncertainties and environmental control, not to mention the cost involved. A natural approach to address the issue is to run model tests, where it is possible to control a great number of variables.
In the desire to develop new methods to evaluate hydrodynamic coefficients and to improve the understanding of the phenomena, this paper proposes different types of free-running tests to be conducted in an experimental ocean basin. An Anchor Handling Tug Supply Vessel (AHTS) scaled model was used to perform the classic turning circle and the novel turning eight, a substitute to the zigzag that fits in limited manoeuvring facilities. Optimizations of mathematical manoeuvring models were applied to estimate the hydrodynamic coefficients with a new proposed metric of manoeuvres comparison. Simulations results were compared with the experimental measurements of the model during the tests. The experimental tests were performed at LabOceano, the Ocean Technology Laboratory of the Federal University of Rio de Janeiro.