bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study of Hydrodynamic Impact on Bubbly Water
Authors: Elhimer Mehdi , El Malki Alaoui Aboulghit , Croci Kilian , Gabillet Céline , Jacques Nicolas
Published: October 2015

The phenomenon of slamming on a bubbly liquid has many occurrences in marine and costal engineering. However, experimental or numerical data on the effect of the presence of gas bubbles within the liquid on the impact loads are scarce and the related physical mechanisms are poorly understood. The aim of the present paper is to study numerically the relationship between the void volume fraction and the impact loads. For that purpose, numerical simulations of the impact of a cone on bubbly water have been performed using the finite element code ABAQUS/Explicit. The present results show the diminution of the impact loads with the increase of the void fraction. This effect appears to be related to the high compressibility of the liquid-gas mixture.
Full Scale Flow Loop Experiments of Hole Cleaning Performances of Drilling Fluids
Authors: Ytrehus Jan David , Taghipour Ali , Sayindla Sneha , Lund Bjørnar , Werner Benjamin , Saasen Arild
Published: October 2015

One important requirement for a drilling fluid is the ability to transport the cuttings out of the borehole. Improved hole cleaning is a key to solve several challenges in the drilling industry and will allow both longer wells and improved quality of well construction. It has been observed, however, that drilling fluids with similar properties according to the API standard can have significantly different behavior with respect to hole cleaning performance. The reasons for this are not fully understood.

This paper presents results from flow loop laboratory tests without and with injected cuttings size particles using a base oil and a commercial oil based drilling fluid. The results demonstrate the importance of the rheological properties of the fluids for the hole cleaning performance. A thorough investigation of the viscoelastic properties of the fluids was performed with a Fann viscometer and a Paar-Physica rheometer, and was used to interpret the results from the flow loop experiments.

Improved understanding of the fluid properties relevant to hole cleaning performance will help develop better models of wellbore hydraulics used in planning of well operations. Eventually this may lead to higher ROP with water based drilling fluids as obtained with oil based drilling fluids. This may ease cuttings handling in many operations and thereby significantly reduce the drilling cost using (normally) more environmentally friendly fluids.

The experiments have been conducted as part of an industry-sponsored research project where understanding the hole cleaning performance of various oil and water based drilling fluids is the aim. The experiments have been performed under realistic conditions. The flow loop includes a 10 meter long test section with 2″ OD freely rotating drillstring inside a 4″ ID wellbore made of concrete. Sand particles were injected while circulating the drilling fluid through the test section in horizontal position.
Validation of the Index to Determine Design Parameters of a WEC for the Cost Optimization of a Wave Farm
Authors: Okamoto Takashi , Fukaya Yutaro , Higo Yasushi
Published: October 2015

An index to estimate the cost of electricity (COE) generated by a wave farm from the design parameters of a wave energy converter (WEC), such as the body size and the generator capacity, was examined to show the validity of index value in this study. The validation tests are performed for three different wave farm settings at three different locations.

The result displays the potential of index to capture the trend of COE value especially when the wave farm size is small. The calculation result of COE reveals that the parameter combination to give better profitability is determined by the balance between WEC construction fee and installation fee. So, it would be different from the optimum size to have the best energy conversion efficiency. It also explains the shift of parameter combination to give the better profitability when the size of wave farm is changed. However, the index contains certain level of error because of the lack of this feature. Therefore, the error becomes larger when the size of wave farm becomes larger. As a result, it was found that the modification of the index is needed to improve the accuracy by including the cost related to the number of buoys in the wave farm.
Reeling Pipeline Material Characterization: Testing, Material Modeling and Offshore Measurement Validation
Authors: Karjadi Erwan , Boyd Helen , Demmink Harm , Thibaux Philippe
Published: October 2015

It is a fact that when a pipeline is installed by the reeling method, it will undergo cyclic plastic straining and the pipe will plastically deform. Due to the applied plastic bending moment, the residual deformation in terms of residual pipe ovality after reeling is difficult to predict by Finite Element Analyses (FEA) without a thorough understanding of the material characterization and changes under cyclic plastic straining.

The paper describes how the material behavior of seamless pipe under plastic strain reeling cycle has been characterized by a comprehensive material testing program including Bauschinger tests and perpendicular loading pre-straining tests. It turns out that for seamless pipe, by looking at the yield stress locus of the material after plastic straining, the reeled pipe material which initially shows isotropic behavior in the un-strained condition will change and evolve to show anisotropic behavior. The material in the hoop direction of the pipe will become more hardened than the material in the longitudinal direction of the pipe. The cross hardening characteristics of material under cyclic plastic deformation have been modeled using the “distortional plasticity” principle and implemented in a user subroutine of an FEA software package.

This paper includes the validation of the ovality prediction by FEA model using the developed material model against the ovality measurement from full scale bend tests at Heriot-Watt University as well as ovality measurements taken during the spooling test and trial of 16″OD pipeline at Carlyss spool base in 2013. The material testing of a sample cut out from Spoolbase test and trial, undergoes spool and un-spool 5 cycles, has been performed to confirm the distortional plasticity hardening behavior obtained from the small scale Bauschinger and perpendicular loading tests.
Drifting Paths of Disabled Vessels
Authors: Selvik Ørjan , Berg Tor Einar , Fathi Dariusz Eirik
Published: October 2015

Many maritime emergency situations involve drifting vessels, and tools to predict drifting patterns have been developed by meteorology institutes, class societies and research companies. It is important to be able to predict a vessel’s drifting path and to estimate when it will drift into waters where grounding is a possible outcome. Such a prediction tool would provide valuable input to the planning of an emergency towing operation to prevent the vessel from grounding or to reduce the impact of the grounding.

In this paper we present the outcomes of a study that investigated the drifting pattern of a vessel with an engine shut-down in the Barents Sea. As part of the ongoing A-Lex project [1], MARINTEK has prepared a VeSim [2] model to investigate the drifting path of a cargo vessel. The outcomes of the study will be used to draw up a technical specification for work to be done to develop an improved ship drift model in Norwegian Meteorological Institute’s (MET Norway’s, [3]) new Halo platform [4]. An improved model will be of great help to those planning emergency towing operations and for positioning of emergency preparedness units with respect to the traffic situation (especially tracks of vessels carrying dangerous goods) and weather forecasts.
The Influence of the Mooring System on the Motions and Stability of a Semi-Submersible Floating Wind Turbine
Authors: Huijs Fons
Published: October 2015

One of the main aspects of a floating offshore wind turbine design is its mooring system, which can strongly influence the floater stability and motions. This is illustrated by considering two catenary mooring systems for the same semi-submersible. The main difference between the two systems is the position of the connection points of the mooring lines on the floater, the so-called fairleads. The philosophy is that the design can be improved by shifting the fairleads to the highest feasible level.

For both mooring systems, the floater motions and stability are assessed. Stability curves are derived, taking both the effect of hydrostatics and the mooring system into account. Floater motions are analyzed using both uncoupled frequency domain calculations and coupled aero-hydro-servo-elastic time domain simulations.

The mooring system is found to have a considerable effect on the floating stability. The effect on the motions is less profound for the considered mooring systems and limited to the low frequency range. Mooring line tensions are however significantly affected by the fairlead position.

It is concluded that, with a well-designed mooring system, a smaller and thus less expensive floater can be used while still meeting the requirements in terms of stability and maximum motions. In addition, the mooring lines may be lighter as well.
Analysis of a Hysteresis IPM Motor Drive for Electric Submersible Pumps in Harsh Atlantic Offshore Environments
Authors: Rabbi S. F. , Sarker M. M. , Rideout D. G. , Butt S. D. , Rahman M. A.
Published: October 2015

This paper presents the analysis of a hysteresis interior permanent magnet (IPM) motor drive for electric submersible pumps. A hysteresis IPM motor is a self-starting solid rotor hybrid synchronous motor. Its rotor has a cylindrical ring made of composite materials with high degree of hysteresis energy. The rare earth permanent magnets are buried inside the hysteresis ring. A hysteresis IPM motor can self-start without the need of additional position sensors and complex control techniques. It does not have any slip power losses in the rotor at steady state which results in less heat dissipation and low electrical losses. When used in an electric submersible pump (ESP) for oil production, it has the ability to automatically adapt itself to the changes in well conditions. In this paper, a bond graph model of a hysteresis IPM motor ESP drive is used to predict the effect of pump shaft geometry on transient behaviour of the drive during start-up. Simulation results show that the hysteresis IPM motor drive has high efficiency, and is better able to maintain its speed during changes in load. Due to increased efficiency and simplified controller requirements, the hysteresis IPM motor is proposed as a replacement for the standard induction motor currently used for downhole ESPs. This is expected to improve ESP performance and reliability which are critical requirements for use in harsh offshore environments such as Atlantic Canada.
An Efficient Time Domain Code for Strength and Fatigue Analysis of Steel Catenary Risers
Authors: Sidarta Djoni E. , Jing Xiaoning , Lambrakos Kostas F. , Burke Roger W. , Webster William C.
Published: October 2015

Steel Catenary Risers (SCRs) are commonly used in the offshore industry. Strength and fatigue performance of SCRs due to waves, currents and vessel motions is typically calculated using time domain dynamic analysis. Strength analysis may involve a large number of load cases for different environments, riser conditions and vessel configurations. Fatigue analysis may involve computation of riser response for hundreds of fatigue sea-states. It is very important for project schedule and cost that the analysis software used is both accurate and computer efficient. This paper presents RodDyn as an alternative time domain analysis tool for SCR strength and fatigue analysis.

RodDyn is a finite element program for dynamic analysis of single-pipe risers. Several publications on this program are available in the literature. The results of dynamic analysis of an SCR for strength and fatigue from RodDyn are compared against the results from ABAQUS. ABAQUS is a general finite element program that has been widely used in the offshore exploration and production industry and has been considered one of the standard finite element programs. Riser dynamic analysis uses time series of vessel motions due to metocean environments at an oblique angle to the plane of the SCR. Von Mises stress per API RP 2RD, strength checks per API STD 2RD and fatigue damage along the riser are presented for both RodDyn and ABAQUS. Time series of effective tension and bending moments at selected locations on the riser are also compared.

The main advantage of using RodDyn for riser analysis is the speed of computation. This paper shows that RodDyn can deliver significant gains in computational speed compared to standard riser analysis software programs without sacrificing accuracy of the computed results.
Structural Response of Ice-Going Ships Using a Probabilistic Design Load Method
Authors: Erceg Boris , Ralph Freeman , Ehlers Sören , Jordaan Ian
Published: October 2015

Ships operating in ice-covered waters experience intense loads from ice features, particularly multiyear ice. Therefore, their structures have to be able to withstand these loads, making structural design paramount. Current formulations of ice class rules do not fully account for the probabilistic nature of ice loads, i.e. scale effects for local ice pressures captured in full-scale measurements. Furthermore, ice class rules do not consider route-specific ice conditions when calculating the design load, i.e. the exposure of the vessel to ice crushing determined by the number and duration of rams. An approach to arctic ship design based on probabilistic methods was developed by Jordaan and co-workers in 1993 and is described in this paper. The approach is used to estimate extreme design loads based on the annual interaction events and the design strategy (target exceedence criteria). The objective of this paper is to select an appropriate ice class for a vessel navigating along the northern sea route, and to compare the design requirements with those determined using the probabilistic approach based on measured data and expected exposure. Local hull pressures have been measured using the USCGC Polar Sea for a range of ice conditions including first year and multi-year ice. Impact conditions similar to those expected along the Northern Sea route were selected and corresponding pressurearea parameters used for input into the probabilistic approach discussed above. This paper will compare the design and response of an exemplary stiffened panel using the described approach to requirements given in Finnish Swedish Ice Class Rules. A case study structure will be analyzed using Finite Element Method for a chosen exposure scenario and target safety level.
Bed Shear Stress Distribution Around Offshore Gravity Foundations
Authors: Tavouktsoglou Nicholas S. , Harris John M. , Simons Richard R. , Whitehouse Richard J. S.
Published: October 2015

Offshore gravity foundations are often designed with complex geometries. Such structures interact with the local hydrodynamics and generate enhanced bed shear stresses and flow turbulence capable of scouring the seabed or destabilizing bed armour where deployed. In the present study a novel bed shear stress measurement method has been developed from the camera and laser components of a Particle Image Velocimetry (PIV) system. The bed shear stress amplification was mapped out around six models of gravity foundations with different geometries. Tests were repeated for two bed roughness conditions. The structures tested included uniform cylinders, cylindrical base structures and conical base structures. The flow field around the models was also measured using PIV.

The results of this study reveal that the conical base structures generate a different hydrodynamic response compared to the other structures. For uniform cylinders the maximum bed shear stress amplification occurs upstream, at an angle of 45° relative to the flow direction, and measurements were found to agree well with numerical results obtained by Roulund et al. (2005). In the case of the cylindrical base structure the maximum amplification occurs upstream at a similar location to the uniform cylinder case. For the conical base structures the maximum amplification of the bed shear stress occurs on the lee side of the structure, with the magnitude dependent on the side slope of the cone. The bed shear stress results were validated against stresses derived from analysis of the flow fields obtained by the PIV measurements performed under the same test conditions.

Conclusions from the study are that the structure with the cylindrical base foundation produces the lowest bed shear stress amplification and that an increase in the bed roughness results in an increase in the amplification of the bed shear stress. These findings have direct implications for design of scour protection. In addition the flow reattachment point behind the foundation is dependent on pile Reynolds number (ReD). This suggests that the results of this study may be extrapolated for higher pile Reynolds using the method described in Roulund et al. (2006).
Progresses in the Development of a Weakly-Nonlinear Wave Body Interaction Model Based on the Weak-Scatterer Approximation
Authors: Chauvigné Camille , Letournel Lucas , Babarit Aurélien , Ducrozet Guillaume , Bozonnet Pauline , Gilloteaux Jean-Christophe , Ferrant Pierre
Published: October 2015

In continuation of [1], this paper presents the progress made towards the development of a new modeling tool based on the Weak-Scatterer approaches. Recent developments are the coupling of the fluid and body solver in order to predict the free motion response of the body. Pressure field over the wetted area is obtained by solving an additional boundary value problem for the time derivative of the velocity potential. Tanizawa’s [2] and Cointe’s [3] formulations for the acceleration condition on the body are revisited. Numerical prediction with the present method for a submerged body in vertical free motion is presented and energy conservation is verified. In order to adapt the mesh to the moving body geometry, advanced mesh moving schemes have been integrated based on radial basis functions [4] and spring analogy methods. In this way it is possible to solve the problem with an Arbitrary Euler Lagrangian formalism and preserve the order of the numerical scheme. However moving mesh methods are limited in time and automatic remeshing generation algorithms have been integrated in order to enable simulating longer durations. Finally, comparisons of wave diffraction and radiation predicted by linear theory, a fully nonlinear BEM solver and the present method are shown.
Characterization of a Wind Tunnel for Use in Offshore Wind Turbine Development
Authors: Newton James M. , Cameron Matthew P. , Urbina Raul , Kimball Richard W. , Goupee Andrew J. , Thiagarajan Krish P.
Published: October 2015

In this work a wind tunnel with an open jet configuration is investigated for use in offshore wind turbine testing. This study characterizes the open-jet wind-tunnel using measurements of the velocity field detailing mean velocities and turbulence intensities with and without a scaled wind turbine. Measurements have been taken downstream to evaluate the expected area of turbine operation and the shear zone. The effects on the flow due to the wake and turbine blockage have also been identified. Additionally, the combination of honeycomb and screens necessary to produce a homogeneous flow at the desired velocity with low turbulence intensity has been identified.

This work provides a useful data set that will be used as a benchmark to evaluate the benefits of recirculating wind tunnels. The data set has resulted in identifying conditions that would prevent producing the desired flows. The data set has also resulted in recommendations concerning the shape of the wind tunnel sections at the University of Maine’s wind-wave (W2) facility to minimize its interactions with the turbine wake expansion, turbine blockage, and the turbine associated wake shear zone.
Partial Safety Factors and Design Fatigue Factors for Design Requirements of Tidal Turbines: A Risk Based Approach
Authors: Simeon Gaizka Zarraonandia , Chen Piing , Ferreira Claudio Bittencourt
Published: October 2015

This paper describes the methodology behind the partial safety factors and design fatigue factors of the DNV GL standard for certification of tidal turbines. The standard follows a risk based approach that allows the adjustment of the design requirements to the identified risk level of the system.

The work undertaken in this study has involved the identification of the uncertainties during the design process. Tidal turbines are located in highly energetic sites which are very difficult to characterise, hence site conditions are one of the largest sources of uncertainty. Key parameters like turbine inflow conditions or predictions of extreme values are still grey areas. Load simulation tools are still quite uncertain and are often dependent on the experience of the people running them.

Both partial safety factors and design fatigue factors have been calibrated to different target safety levels with due account for the uncertainties introduced by load models as well as site characterisation. The different target safety levels have been selected in accordance to the risk associated to structural failures of tidal turbine support structures and aim for a more streamlined design from the safety requirements point of view.
Deterministic Simulation of Breaking Wave Impact and Flexible Response of a Fixed Offshore Wind Turbine
Authors: Bunnik Tim , Helder Joop , de Ridder Erik-Jan
Published: October 2015

The effects of operational wave loads and wind loads on offshore mono pile wind turbines are well understood. For most sites, however, the water depth is such that breaking or near-breaking waves will occur causing impulsive excitation of the mono pile and consequently considerable stresses, displacements and accelerations in the mono pile, tower and turbine.

Model tests with a flexible mono pile wind turbine were carried out to investigate the effect of breaking waves. In these model tests the flexibility of the turbine was realistically modelled. These model tests were used for validation of a numerical model for the flexible response of wind turbines due to breaking waves. A focusing wave group has been selected which breaks just aft of the wind turbine.

The numerical model consists of a one-way coupling between a CFD model for breaking wave loads and a simplified structural model based on mode shapes. An iterative wave calibration technique has been developed in the CFD method to ensure a good match between the measured and simulated incoming wave profile. This makes a deterministic comparison between simulations and measurements possible. This iteration is carried out in a 2D CFD domain (long-crested wave restriction) and is therefore relatively cheap. The calibrated CFD wave is then simulated in a (shorter) 3D CFD domain including a (fixed) wind turbine. The resulting wave pressures on the turbine have been used to compute the modal excitation and subsequently the modal response of the wind turbine. The horizontal accelerations resulting from this one-way coupling are in good agreement with the measured accelerations.
Nonlinear Analysis of Axisymmetrically Wrinkled Pipes Under Axial Loads and Internal Pressures
Authors: Dhar Ashutosh Sutra , Muntakim Abu Hena
Published: October 2015

Nonlinear finite element analysis of axi-symmetrically dented/wrinkled pipe has been presented in this paper. The pipe including surrounding soil was modelled using three different approaches to indicate the effects of modelling approaches on the simulation of pipe behavior. In the first approach, pipe was modelled with the geometry of the dented/wrinkled pipe without consideration of any residual stress and stress history. In the second approach, residual stress was applied at the nodal points of the pipe geometry modelled as in the first approach. In the third approach, a dent/wrinkle was created on the pipe wall through applying nodal displacements to include residual stress as well as the stress history effects.

The analysis revealed that the first approach provides an un-conservative estimation of the pipe capacity. The second approach provides a reasonable estimation of the pipe capacity for elastic perfectly plastic material. However, the second approach provides a conservative estimation for strain hardening material, since pipe stress history is not considered. For strain hardening materials, both residual stress and the stress history should be considered for the simulation of the pipe behavior. The surrounding soil appears not to contribute to the capacity of the pipes under the loading conditions investigated.
Systematic Testing of the Fatigue Performance of Submerged Small-Scale Grouted Joints
Authors: Schaumann Peter , Raba Alexander
Published: October 2015

With an increasing demand for renewable energy, offshore wind farms become more and more important. Within the next 15 years the German government intends to realize offshore wind farms with a capacity of 15 GW of electrical energy. This corresponds to approximately 3000 to 4000 new turbines.

The grouted joint is a common structural detail for the connection between substructure and foundation piles in offshore wind turbine structures. For lattice substructures such as jackets, the connection is located just above the seabed and is permanently surrounded by water.

Prior investigations by Schaumann et al. showed that the surrounding water may have an impact on the fatigue performance of grouted joint specimens. Thus far, very few results of submerged fatigue tests on grouted joint specimens are published and their statistical reliability is insecure.

Within this paper, 24 individual test results are presented. Regarding test parameters, the focus is set on two different applied load levels, two different loading frequencies and two different grout materials. All parameters are varied in a factorial experiment and are statistically evaluated.

The evaluation shows that load level and loading frequency have a significant effect on the fatigue performance of the connection. Moreover, both effects are significantly correlated. For the used grout materials no significant impact is visible, which can be explained by their similarity regarding mechanical properties and micro structure. Furthermore, the mean displacement and the stiffness degradation of the specimens during fatigue tests are discussed in detail in the paper.

In conclusion, previously published results on the fatigue performance of submerged small scale grouted joint specimens can be confirmed. Load level as well as loading frequency can be stated as most relevant parameters for the fatigue performance.
Corrosion Effects on the Strength of Steel Pipes Using FEA
Authors: Mondal Bipul Chandra , Dhar Ashutosh Sutra
Published: October 2015

This paper presents a finite element investigation on the strength and deformation characteristics of corroded steel pipes with corrosion on the exterior and interior surfaces of the pipes considering different corrosion parameters such as circumferential extent (width) of corrosion, ratio of corrosion width to pipe diameter and the locations of corrosion. The finite element analysis was performed using a commercially available general purpose finite element program, ABAQUS/Explicit. The study reveals that localized bending develops on the pipe wall within the corroded zone that extent up to a certain distance (1 to 1.5 times the corrosion dimension) in the non-corroded area. The localized bending causes stress concentration in the vicinity of the corroded area that is not well captured in the current design standards (i.e. modified ASME B31G). As a result, the modified ASME B31G method overestimated the pipe capacity comparing to the capacity calculated based on the finite element analysis. A pipe designed using the modified ASME B31G method is expected to provide a factor of safety less than the design factor of safety. The effects of circumferential extent of corrosion appears to be less compared to the effects of longitudinal extent of corrosion. The exterior corrosion was found to be more detrimental in comparison with the interior corrosion.
Basic Plan of Medi-Float on Big Disaster Installed in the River
Authors: Eto Hiroaki , Sato Chiaki , Masuda Koichi , Ikoma Tomoki , Shimizu Ken , Kuroyanagi Akio , Yamaguchi Junko
Published: October 2015

An innumerable number of buildings in the coastal part of the east side of Japan were devastated by the Great East Japan Earthquake and Tsunami. Medical institutions also suffered the damage caused by tsunami, and the function to carry out the medical act has been spoiled. And the disabled concentrated on the medical institution which avoided tsunami damage. Under such circumstances, assistance from the water area began three days after the earthquake disaster, and much support supplies reached the stricken area. It was revealed that the support from the water area including the river was extremely effective against the stricken area. And then, the Tokyo Inland Earthquake disaster was assumed, floating medical support system (hereafter, Medi-Float) installed in the quay of Arakawa River in Tokyo was proposed. Medi-Float is movable; furthermore, it is built in the structural system of having very high isolation characteristics. The float proposed in this study is a facility based on a completely new concept and hence it is difficult to get approval as simply a hardware structure or facility, even if it is safe. Our study considers the constraints with respect to installing the system on the river as the basic plan of the specific Medi-Float. It takes into account the floor planning and flow planning based on operational methods, considers scale planning and weight calculation and the structural strength of the float foundation. The study conducts basic plan of the feasibility of the first-of-its-kind medical float as a marine structure. As the next step, the research on dynamic behavior of Medi-Float will be started, and the validity of this design is verified, technical issues in the design of the Medi-Float should be clarified.
Simulation of Safety-Relevant Situations Regarding the Interaction of Service Ships With Offshore Wind Turbine Plants
Authors: König Marcel , Düster Alexander , Ferreira González Daniel , Abdel-Maksoud Moustafa
Published: October 2015

When offshore wind turbine plants require servicing, crew transfer vessels are used to bring the maintenance personnel to the plant. The berthing maneuver is a coupled process governed by the ship’s motion in the swell and the contact between the fender and the boat landing. Our research aims to simulate the berthing maneuver in order to identify conditions to ensure safe landing operations and to ascertain how future transfer concepts can help to avoid severe accidents. To this end, we take advantage of a partitioned solution approach which has already been proven to be effective for various kinds of multiphysics problems and which allows for the reuse of existing dedicated solvers for the solution of the subproblems involved.
A Multiscale Mechanistic Model for Slow Transient Two-Phase Gas Condensate Flows in Pipelines
Authors: Kamhawi Khalid , Zhao Yabin , Finch Liam
Published: October 2015

Various technical, commercial and operational requirements and conditions warrant the modelling of gas condensate pipelines as two-phase flows. Although phenomenological descriptions of two-phase flows are commonly used in the Oil and Gas Industry, the thermal-hydraulic complexities of such systems mean that a number of mechanistic formulations are available, some emphasising accuracy at the expense of computational efficiency, others preferring a more simplified approach. This article proposes a fully mechanistic slow transient model of two-phase condensate gas flows in pipelines, where the slip relation is derived from first principles using a mutliscale expansion method. Representative steady state and transient case studies for different operational conditions are simulated and solved numerically. Results are analysed and validated against an industry standard Two-Fluid Model based software.
A Study on Development of the Performance Analysis Method of the Floating OWC-WEC Using the MPS Method
Authors: Sasahara Yutaro , Masuda Mitsuhiro , Minami Kiyokazu
Published: October 2015

When concrete examination towards utilization is needed, it is necessary to estimate the safety and the performance of a floating Oscillation Water Column (OWC)-type wave energy converter under abnormal oceanographic phenomenon such as large waves, wave impact force, deck wetness and complex motion of mooring system. Therefore, to choose a proper numerical method is important. This present paper describes a fundamental study about estimation of safety and performance of floating OWC-type wave energy converter using the two-phase flow MPS method. In this research, firstly, new algorithm is installed in order to solve problems of the two-phase flow MPS method. Secondly, applicability to an response analysis of a wharf installation type OWC-WEC of the improved MPS method is examined by wave pressure acting to the OWC-WEC and response in the air chamber of the OWC-WEC.
The Northern Sea Route vs the Suez Canal Route: An Economic Analysis Incorporating Probabilistic Simulation Optimization of Vessel Speed
Authors: Way Brent , Khan Faisal , Veitch Brian
Published: October 2015

While previous studies have examined the economics of shipping from Europe to Asia via the Northern Sea Route (NSR) versus the Suez Canal Route (SCR), most have not adequately accounted for the variability in input parameters such as the cost of fuel or the amount of ice encountered on a voyage. Furthermore, no prior study has attempted to utilize speed optimization as part of the analysis.

Because the rate fuel consumption for propulsion is intrinsically linked with vessel speed, reducing speed can create the potential for large savings in fuel costs, along with the added benefit of reduced emissions. However, the reduced speed means a longer transit time, meaning increases in other time based costs, such as daily pay for a ship’s crew. The question then becomes what is the optimal speed?

This paper examines the use of speed optimization to determine whether it is potentially more profitable for a container shipping company to ship from Rotterdam to Yokohama through the SCR year round (Option A) or to ship through the NSR during the months it is passable while using the SCR for the remainder of the year (Option B). A probabilistic model is presented to determine average per trip profits for both options A and B. This model is used in conjunction with a simulation optimization technique to determine the optimum speeds to maximize average per trip profitability for each option. The results show that probabilistic simulation optimization of vessel speed may better inform shipping companies as to the financial impacts of the speeds that they choose to use for shipping and thus enable better decision making as it pertains to both route choice and ships’ speeds. The analysis indicates that speed optimized container shipping year round through the Suez Canal appears to be the more profitable of the 2 options.
Fatigue Analysis of a Thin Cover Plate Structure in a Light Craft
Authors: Köder Till , Bohlmann Berend
Published: October 2015

Experimental fatigue analysis of a fillet-welded cover plate detail (‘floating frame’) of small and light craft was carried out at Kiel University of Applied Sciences. The structural detail is an intersection of longitudinal deck stiffener and transverse web frame with a plate thickness of 3.5mm and a doubling length of 100mm. Manual gas metal arc welding was used for the production of the 46mm long transverse fillet welds. The load-controlled constant amplitude fatigue tests at stress ratio R = 0 were supported by 3D finite-element analysis based on laser scans of the weld seams. Structural hot-spot stress, stress linearisation and Xiao and Yamada’s 1mm geometrical stress approaches were applied to the specimens as well as the notch stress concept with reference radii rref = 0.05mm and 1.00mm.
Development of PTO-Sim: A Power Performance Module for the Open-Source Wave Energy Converter Code WEC-Sim
Authors: So Ratanak , Simmons Asher , Brekken Ted , Ruehl Kelley , Michelen Carlos
Published: October 2015

WEC-Sim (Wave Energy Converter-SIMulator) is an open-source wave energy converter (WEC) code capable of simulating WECs of arbitrary device geometry subject to operational waves. The code is developed in MATLAB/Simulink using the multi-body dynamics solver SimMechanics, and relies on Boundary Element Method (BEM) codes to obtain hydrodynamic coefficients such as added mass, radiation damping, and wave excitation. WEC-Sim Version 1.0, released in Summer 2014, models WECs as a combination of rigid bodies, joints, linear power take-offs (PTOs), and mooring systems. This paper outlines the development of PTO-Sim (Power Take Off-SIMulator), the WEC-Sim module responsible for accurately modeling a WEC’s conversion of mechanical power to electrical power through its PTO system. PTO-Sim consists of a Simulink library of PTO component blocks that can be linked together to model different PTO systems. Two different applications of PTO-Sim will be given in this paper: a hydraulic power take-off system model, and a direct drive power take-off system model.
Analysis of Aerodynamic Performance of Floating Wind Turbines Using CFD and BEMT Methods
Authors: Make Michel , Vaz Guilherme , Fernandes Gerson , Burmester Simon , Gueydon Sebastien
Published: October 2015

Scaling effects caused by applying Froude-scaling to both wind and waves during model-testing of floating offshore wind turbines (FOWTs) results in poor model-scale aerodynamic performance of geometrically scaled turbines. This led to the “performance-scaled” MARIN Stock Wind Turbine (MSWT) which showed to be successful in obtaining the correct thrust loads at model-scale conditions. Additionally it was found that conventional blade-element-momentum-theory-based (BEMT) modelling tools are not suitable for model-scale conditions.

Recent research in which these problems have been addressed are presented in this paper. First a 3D CFD study was performed in which the behaviour of the flow over the commonly studied NREL 5MW baseline turbine and the MSWT geometries was performed. Both model and full-scale conditions were studied for a fixed non-moving platform and rotor-only turbine. It was found that scaling effects are indeed significant and a highly three-dimensional and additionally separated flow was observed. Based on these findings two methods were proposed to expand the applicability of BEMT-based tools to off-design and modelscale conditions.

First, instead of using commonly used 2D XFOIL data, 2D CFD RANS data was used. The use of purely 2D data from 2D CFD RANS computations did however not result in the desired improvements when compared to XFOIL-based results. The second proposed method is based on the use of 2D airfoil data obtained by post-processing of 3D flow data coming from 3D CFD computations. This new approach was shown to be successful and can therefore be extremely useful for future model-scale FOWT testing campaigns to do preliminary performance predictions. All BEMT-based and CFD results presented in this paper were compared to model-scale experimental data of the NREL 5MW turbine and the MSWT over the full range of TSR.
Comparative Physical and Numerical Modeling of Riser-Seabed Interaction
Authors: Barrett John , Phillips Ryan , Macneill Andrew
Published: October 2015

Offshore steel catenary riser-seabed interaction is complex with uncertainty in design for riser fatigue and longevity of the riser system. A numerical finite element tool was developed to capture the non-linear, hysteretic behaviour of riser-seabed interaction capturing trench formation with successive riser motions. The design and centrifuge testing of a three axis (translational degrees of freedom) actuator are also presented. This paper presents finite element analysis comparisons to physical test data as well as the influence the trench formation has on altering riser bending moment in the touchdown zone.
Enhanced Collapse Resistance for Different D/t Ratios of UOE Pipes for Ultra Deepwater Application
Authors: De Lucca Rodrigo , Solano Rafael F. , Swanek Doug , de Azevedo Fabio B. , Arroyo Fábio , Alves Hélio , Silva Ronaldo
Published: October 2015

Energy consumption outlook shows that the demand for Oil and Gas is increasing worldwide and since most of the undemanding reserves are already being explored, new reserves means longer distances from the shore and increasing water depths, of up to 3,000 meters. Collapse resistance has become a key factor in the design of pipelines for ultra-deepwater applications. UOE process is commonly used for manufacturing pipelines of large diameter and the cold work involved in this forming process modifies the mechanical properties of the pipes. This paper presents the effect of thermal treatment on final material properties, proving the validity of enhancing collapse for different D/t, as allowed by DNV-OS-F101 αFab, and extending what has been shown as valid on previous studies. In this work, the inputs for the processing strategies are presented, along with coupon compression testing and full scale testing, in order to qualify the selected route as compliant with producing pipes with αFab equal to 1, for usual D/t combinations. An analysis of the predicted collapse pressure compared to the real collapse pressure of the pipes is also presented. The extension of the qualification process achieved successful results and allows the use of a fabrication factor equal to 1 in ultra-deepwater offshore pipeline projects. This enables the reduction of wall thickness, generating reductions in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.
Comparison of Real-Time Measured and Predicted Wellhead Fatigue Performance in a Deepwater Drilling Operation
Authors: Mackenzie James , Murdoch Neil , Killbourn Stuart
Published: October 2015

This paper discusses the use of a real-time monitoring system to track wave driven fatigue damage at critical locations in a subsea well during a 290-day drilling operation in the Mediterranean Sea. Real-time monitoring was employed due to up-front finite element (FE) analysis predicting fatigue damage rates of sufficient magnitude that the required safety factor would not be met.

LMRP/BOP motions were recorded using two subsea monitoring units (each containing accelerometers and angular rate sensors). These were installed on the LMRP and above the lower flex joint. The accelerometer signals were used to deduce the static inclination of the well and the angular rate signals the dynamic inclination due to vessel motion and wave loading on the riser. Data was transmitted in real-time to a central processing unit on board the vessel. This converted the motion data into fatigue damage accumulation using non-linear transfer functions derived from the FE model. The damage was displayed in a simplified format for use in decision-making.

The recorded data revealed the motions of the LMRP/BOP and hence the damage rates in the well to be considerably less than predicted by the FE analysis. The damage rates derived from the monitoring system therefore served as a continuously updating demonstration that an acceptable margin of safety against suffering a fatigue failure was being maintained thus permitting drilling to proceed safely.

A subsequent benchmarking study which additionally involved processing of recorded vessel motion data, current data and seastate data was undertaken to identify possible reasons for the differences between the predicted and measured LMRP/BOP motions. This showed that conservative assumptions made on the soil stiffness (due to limited availability of data), differences between the predicted and measured riser natural periods and differences between the predicted and measured vessel motions all contributed to the LMRP/BOP motions and hence the damage rates predicted by the up-front FE analysis being larger than measured in the field. The systematic identification of the factors which contributed to the differences between the predicted and measured response is described in this paper. Areas where further work would be of value to help improve the reliability of up-front, analytically predicted fatigue damage rates are also discussed.
Predictive Residual Ovality for Reel-Laid Pipelines in Deepwater
Authors: Sriskandarajah T. , Rao Venu
Published: October 2015

Accurate determination of residual ovality is an important parameter for a successful deployment of single pipeline and pipe-in-pipe in deep waters wherein the integrity of empty pipes during installation depends upon the collapse resistance under external hydrostatic pressure. The reel-lay process of installation during which pipeline undergoes multiple strain cycles due to spooling, reeling and straightening has a significant bearing on pipe ovalisation and hence accurate determination residual ovality at the end of straightening process is one of the key inputs.

It is industry practice to use numerical finite element analysis techniques to predict residual ovality of pipelines as full scale testing is expensive and time consuming. In view of the importance of residual ovality on the pipeline integrity particularly for deepwater applications, an integrated approach of testing and finite element simulation have been used to identify the correct numerical model that predicts residual ovality accurately. This paper discusses the full scale tests performed which include material testing and bend tests performed to simulate spooling and straightening process and the pipeline deformations recorded using laser measurements at different cycles of bending process. The paper presents a brief summary of numerical finite element analyses performed to validate the test results and the effect of element types and material models used in the finite element analyses on the predictability of residual ovality.

The material evolution models and their effect on the predictability of remaining ovality are discussed in the paper. Comparisons are made on the predictive residual ovality for reel lay process on single pipe and pipe-in-pipe. The effect of residual ovality on the pipeline integrity for the lateral buckling limit state under combined bending and external pressure are discussed in the paper.
Determination and Mitigation of Hydrodynamic Loads in an Open FPSO Turret by Model Tests
Authors: Martin Bruce , Carrico Todd
Published: October 2015

When transiting to and from the field, disconnectable FPSOs have an open moonpool inside the turret where the buoy is normally situated. Inside the turret are a number of internal components designed to interface with the buoy. These components represent a large capital investment and are critical to FPSO operation. During adverse weather conditions, there is a potential for large hydrodynamic loads on these components due to wave action and the vessel’s seakeeping response. Deriving realistic design values for this equipment can be challenging due to the complex nature of the fluid dynamics inside the turret. This paper describes a unique model test campaign undertaken for a cyclonic region FPSO. It details the findings of using a highly detailed turret model to verify hydrodynamic design loads. Results about the turret’s natural modes are discussed. Correlation between the hydrodynamic loads inside the turret with the vessel’s seakeeping response is also investigated. The influence of draft and forward speed with respect to the hydrodynamic loading is presented. Based on observations made during the test campaign, the worst loading case is likely to occur during the initial transit to site. A possible mitigation method was investigated in the form of a temporary cover plate, effectively closing off the moonpool.