bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computational Fluid Dynamics Approach to Predict Pressure Drop and Flow Behavior in the Near Wellbore Region of a Frac-Packed Gas Well
Authors: Molina Oscar , Tyagi Mayank
Published: October 2015

Well completion plays a key role in reservoir production as it serves as a pathway that connects the hydrocarbon bearing rock with the wellbore, allowing formation fluids (e.g. oil, gas, water) to flow into the well and then up to production facilities on the surface. Frac-packing completion (F&P) is a well stimulation technique that vastly increases the fluid transport capability of the near wellbore region in comparison with the original formation capacity by filling fractures and perforation tunnels with high-permeability proppant, thus enabling higher production rates for the same pressure drop. Hence, it is of interest for the production engineer to have an accurate description of the actual and predicted production performance in terms of pressure drop and flowrate after the F&P completion process is done. However, in developing a mathematical model of this scenario two critical challenges should be faced: (a) as fluid flows at high flowrates it begins to deviate from linear behavior, i.e. Darcy’s law is no longer valid, (b) compressible fluid flow behavior in the near wellbore region cannot be intuitively predicted due to the geometrical complexity introduced by the well completion (e.g. perforation tunnels and fractures). Additionally, this kind of mathematical model must take into account the existence of three different domains: reservoir (porous, low permeability), completion region (porous, high permeability), and free flow region.

In view of these complications, this study presents a computational approach to model and characterize the near wellbore region with F&P completion using computational fluid dynamics (CFD) modeling, combining a non-linear (non-Darcy or Forchheimer) real gas flow in porous media with a turbulence model for the free flow region. This study is classified into three parts: 1) verification case, 2) Darcy vs. non-Darcy flow, and 3) erosion analysis. All simulation cases are assumed to be isothermal, steady state gas flow. Streamlines are implemented to identify the possible kinds of flow regimes, or patterns, in the near wellbore region and it is shown that gas flow pattern can be high unpredictable. Turbulence production and erosional velocity limit are also analyzed. Finally, mathematical correlations for well completion performance of this particular case study are derived using data curve fitting.

In conclusion, the CFD approach has proven to be a powerful yet flexible computational tool that can help the production and/or reservoir engineer to predict flow behavior as well as production performance for a gas producing well with F&P completion, while providing an insightful graphical description of pressure and velocity distribution in the near wellbore region.
Sensitivity of Vessel Responses to Environmental Contours of Extreme Sea States
Authors: Armstrong Curtis , Chin Christopher , Penesis Irene , Drobyshevski Yuriy
Published: October 2015

A comparative study of two methods for the generation of the environmental contours is presented investigating the sensitivity of the predicted extreme vessel responses to the type of the contour lines. Two approaches for the generation of environmental contours of the significant wave height and peak period are compared: the Inverse First Order Reliability Method (IFORM) and Constant Probability Density (CPD) approach. Case studies include several global responses of a ship-shaped weather-vaning vessel and a semisubmersible platform. The case studies reveal that the differences between the IFORM and CPD contours are more pronounced in the range of long wave periods. Vessel responses which are less sensitive to long wave periods exhibit less difference (less than 1.0%) in their maximum values between the two types of contours. In contrast, responses which are sensitive to long wave periods show significantly larger differences of up to 7.0%. Uncertainties also exist in the predicted extreme responses where the environmental contour and the response isoline behave tangentially. Differences between the extreme responses produced by the two contours generally decrease with an increase in return period; however exceptions exist due to the tangential behaviour. It is advised that these sensitivities should be taken into consideration when the environmental contours are used in the design.
Riser Configuration Design for Extreme Shallow Water With Surrogate Model Based Optimization
Authors: Chen Jinlong , Yan Jun , Tang Minggang , Yang Zhixun , Yue Qianjin
Published: October 2015

The aim of this paper is to study the optimization design of a steep wave riser for extreme shallow water based on radial basis function (RBF) surrogate model approach. As the design of riser configuration is rather time consuming and exhaustive due to the nonlinear time domain analysis and large quantities of load cases, it would be more difficult when we need to deal with some extreme design such as in extreme shallow water. The surrogate model in this paper is constructed with RBF networks from the samples obtained by optimal Latin hyper cubic sampling and time domain analysis in a given design space. Then, a hybrid optimization is performed based on the established surrogate model. An optimized design is finally found to meet the design criterion with high accuracy and efficiency, even all the samples fail to meet the curvature criterion.
Desingularized Boundary Integral Methods With Application in Wave Hydrodynamics
Authors: Cao Yusong , Beck Robert F.
Published: October 2015

Desingularized boundary integral equation methods (DBIEM) and their applications in water wave dynamics and body motion dynamics over the past 30 years are reviewed. In solving the potential flow problem for wave dynamics, unlike conventional boundary integral methods, a DBIEM separates the integration surface and the control (collocation) surface, resulting in a BIE with non-singular kernels. The desingularization allows simpler and faster numerical evaluation of the boundary integrals, and thus a fast numerical solution. The paper reviews the fundamental aspects and advantages of DBIEMs. Examples of applications of DBIEMs in wave dynamics and body motion dynamics are given and the outlook of future DBIEMs development is discussed.
Structure Analysis of Flexible Pipe End Fitting Seal System
Authors: Li Xiangyun , Du Xiaying , Wan Jun , Xiao Hui
Published: October 2015

End fitting is one of the most important equipment of the flexible pipe with the function of terminating all the pipe layers, sealing and venting gas. Seal system is the weakest component of the end fitting which is easy to fail under functional and environmental load. This paper addresses the seal performance of the flexible pipe end fitting seal system used in deep waters. The finite element model for flexible pipe end fitting seal system is established in software of ABAQUS to perform the parameter sensitivity analysis on different parameters with the nonlinear contact analysis. The rules of seal and mechanical performances of flexible pipe end fitting seal system on the key parameters under different conditions are studied. The technique proposed in this paper will provide further references for the design of flexible pipe end fitting seal system.
A Method for Deriving Infragravity Wave Design Criteria in Shallow Water
Authors: Sheikh Rizwan , Ewans Kevin
Published: October 2015

Infragravity waves are long waves with periods of 30 to 300 seconds. They are most apparent in shallow-water and can have a large impact on the response of moored vessels, particularly large tankers such as LNG vessels, with long natural periods. A method for estimating infragravity wave design criteria for a shallow-water location is demonstrated. The method uses a combination of hindcast wave data and an idealised model for simulating infragravity waves. By way of example, a case study on the application of the Ideal Surf Beat (IDSB) model to simulate infragravity waves in the coastal waters of Barrow Island, Australia, and the subsequent estimation of extreme criteria quantifying the infragravity wave energy for a possible export berth location, is described.
Validation of Twistlocks in Modular Offshore Platform Designs for the Arctic
Authors: Michel Josefine , Kaeding Patrick
Published: October 2015

The University of Rostock has generated dimensioning equations to calculate the strength of twistlock systems under non-standard loading conditions on offshore platforms in the POLAR project in the last years. These dimensioning equations have been presented on previous OMAE conferences. In this paper ultimate strength analyses are conducted to assess the safety margin between elastic design and final rupture. The validation of the local system is shown and the results of the experiment and the simulation are analyzed and compared. In these experiments twistlock systems are subjected to cyclic loads, long-term tensile load at design level and ultimate loads. The experiments are conducted with a heavy duty hydraulic test rig. The results show agreement between experiment and simulation with regard to the rupture behavior and the force-displacement relationship.
Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces
Authors: Guzel Bulent , Korkmaz Fatih C.
Published: October 2015

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces.

In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.
Mission Based Ship Design Under Uncertain Arctic Sea Ice Conditions
Authors: Choi Minjoo , Erikstad Stein Ove , Ehlers Sören
Published: October 2015

For the design of an ice-going ship, determining its ice-capability is one of the key design aspects. Excessive ice-capability increases the ship’s acquisition cost and reduces its deadweight capacity. On the other hand, less ice-capability limits its serviceable area and it decreases the probability for the ship to complete its given/expected missions successfully. The ice conditions, which the ship would encounter during its operations, are dependent on its route planning, and they become a basis for the determination of its ice-capability. For the design of an ice-going ship, which is going to be operated under constant operational conditions, static route analysis or use of historical voyage data is sufficient to estimate its required ice-capability. However, if the operational conditions change dynamically, like the Arctic sea ice conditions, a dynamic route analysis is needed. Otherwise, the required ice-capability tends to be over-estimated by the static analysis. Sea ice conditions in the Arctic change dynamically from hour-to-hour. In addition, the forecast of its operational conditions has a high uncertainty due to lack of understanding of the Arctic sea ice. Thus, for the design of a ship for Arctic operation, we carry out transit simulations in a dynamic and stochastic manner in this paper and estimate the required ice-capability from the simulations’ result.
Effect of Nano and Micro Sized Particle Additives on the Mechanical Strength of Cement Plug
Authors: Belayneh Mesfin , Aadnøy Bernt S.
Published: October 2015

Cements in oil wells are exposed to high temperatures, a high pressures and a degrading environment. These affect the mechanical strength of the cement over time. Cement is often part of well integrity problems, sometimes creating leak paths to surface, but also allowing sour reservoir gases to corrode casings.

Poor cement bond quality and casing corrosion are two fundamental problems with oil well cements. This paper presents the effect of vegetable fiber, nano- and micro particle additives on cement slurry. The mechanical strength of the cement plugs were analyzed through sonic measurement and uniaxial compressive test. The internal structure of the cement plugs were analyzed through Scanning Electron Microscope (SEM).

The test results show an improved internal structure, higher load carrying capacity, longer deformation and higher modulus of resilience.
Designing Drilling Fluids to Combat Circulation Losses for Arctic Environments
Authors: Belayneh Mesfin , Aadnøy Bernt S.
Published: October 2015

Drilling fluid plays a key role in an efficient drilling operation to minimize problems such as wellbore collapse, circulation losses and stuck pipe. Well instability problems are costly as they increase the non-productive time and the overall budget (1) (2). Well instability problems controlled by designing appropriate mud density and fluid properties that controls the well. The fracture sealing ability of a drilling fluid is one very important of the drilling mud.

This paper presents design of water-based drilling fluids and results from laboratory experiments to quantify the loss circulation performance of drilling fluids.

Because it is preferable to use oil-based muds in some well sections, the paper will also include a recent study on how to minimize losses when using oil based muds. Here uses of micro/nanoparticles have shown to reduce filtrate losses and to build barriers that are more efficient during circulation loss events.

All the tests presented are at low temperature, which is suitable for Artic environments.
Experimental Investigation of Settling Velocity of Natural Sands in Power-Law Fluid Using Particle Image Shadowgraph
Authors: Shahi Shivam , Kuru Ergun
Published: October 2015

In this study a new experimental technique, particle image shadowgraph (PIS), is used to investigate the settling velocity of natural sand particles in Power-law fluids. The particle settling velocity measurements are conducted within the Reynolds number of range of 0.01 to 17.00. Natural sands with mean sieve diameters in the range, 0.35 mm – 1.4 mm, are used. Six different equivalent diameter definitions are used to characterize size of the natural sand particles. Using the size and shape measurements in conjunction with PIS, correlations between the mean sieve diameter and equivalent diameters are obtained.

Empirical correlations for predicting the settling velocity of sand particles in Power-law fluids are developed. Multiple linear regression analyses are performed with each fluid data and empirical coefficients for the models are also reported as functions of n and K. The models presented in the study give an average error of less than 20%. In addition, the multiple linear regression tools are applied to enhance the efficiency of the correlations by 3–5%. One of the major contributions of this study is that one can use any associated diameter to predict the settling velocity, which leads to greater flexibility.
Design of Ship Weight Reduction Based on Reliability Analysis of Longitudinal Bending Strength
Authors: Ren Huilong , Zhang Qingyue , Jiang Xueyun , Hu Yumeng
Published: October 2015

As the focus of the structural design, the form and dimension of components in the mid-ship section reflect the general characteristic of the whole ship, thus playing a significant role in the weight and structural strength of the whole ship. However, traditional deterministic methods of structural strength assessment will bring excessive safety margin, which will lead to excessive weight of ship structure. In this paper, the optimization model was built in view of ship longitudinal bending strength reliability analysis by MATLAB software. With the information of wave loads forecast and that of the section bending strength, the failure probability was obtained. Objective function was the weight of mid-ship section, and optimization variables were the size of sectional components, and the constraints were reliability index and component size limits were required by relevant norms. Combined with the optimization model, genetic algorithm toolbox integrated in MATLAB was applied to study mid-ship section optimization. Results of the examples showed that in the case that the limiting conditions were satisfied, the weight of mid-ship section was reduced to a certain extent, which meant that this method was effective for mid-ship section optimization.
Intermolecular Forces in Clathrate Hydrate Related Processes
Authors: Meindinyo Remi-Erempagamo T. , Svartås Thor Martin
Published: October 2015

The thermodynamics and kinetics of clathrate hydrate formation processes are topics of high scientific interest, especially in the petroleum industry. Researchers have made efforts at understanding the underlying processes that explicate the macroscopic observations from experiments and other research methods of gas hydrate formation. To achieve this, they have employed theories founded upon force related intermolecular interactions. Some of the theories and concepts employed include hydrogen bonding, the Leonard Jones force principle, and steric interactions. This paper gives a brief review of how these intermolecular interaction principles have been understood, and used as tools, in explaining the inaccessible microscopic processes, that characterize clathrate hydrate formation. It touches upon nucleation, growth, and inhibition processes.
Experimental Observation on a Controllable Underwater Towed Vehicle With Vertical Airfoil Main Body
Authors: Wu Jiaming , Chen Jian , Xu Ying , Jin Xiaodong , Lu Lihua , Chen Yuqing
Published: October 2015

An alternative type of controllable underwater towed vehicle is proposed. The vehicle is composed of horizontal fixed main wing, adjustable wing flap, and a vertical airfoil main body above which two torpedo-shaped buoyant cylinders are symmetrically fixed. The adjustable wing flap serves as an actuator for deflection of the horizontal fixed main wing to produce enough downward lifting force to the towed vehicle running at a required water depth. Principal function of the torpedo-shaped buoyant cylinders is to create a righting moment or a favorite roll damping for attitude stability of the vehicle during towing operation. Meanwhile two ducted propellers are installed at the sterns of the buoyant cylinders to provide an induced turning moment for the vertical airfoil main body, which in turn produce a driving force for the vehicle in lateral motion.

Results of our laboratory experiments indicate that flexible attitude and trajectory manipulations to the vehicle in multiple degrees of freedom can be achieved with the structural style and control mechanisms of the proposed vehicle. The manipulations to the vehicle with the proposed control mechanisms are accomplished by a joint operation of controlling the rotational speeds and directions of the ducted propellers and/or adjusting the deflection of the wing flap. By means of the proposed structural style and control manner, difficulty in designing control system of the vehicle can be reduced greatly, and stronger self stability of the vehicle during its survey towing can be guaranteed.
A Study on Resistance Performance for Various Trim Conditions and Bulb Shapes on a Container Ship Under Slow Steaming
Authors: Park Hyun-Suk , Seo Dae-Won , Han Ki-Min , Kim Dae-Heon , Ha Tae-Bum
Published: October 2015

Hull form had been unavoidably optimized for a single speed condition, normally a contract speed at design draft in the past many years due to various reasons such as limited design period, less advanced data processing capacity of a computer and so on. For this reason, for maximizing present ship’s operating efficiency, additional analysis relevant to resistance performance for slow steaming condition is newly required since the original hull form for this study also was developed about 10 years ago.

In this paper, the resistance performances corresponding to various trim conditions are investigated not only for ship’s original contract speed (Fn: 0.255) but for slow speed (Fn: 0.163∼0.183) by slow steaming.

Through this study, it can be accomplished to identify the optimum trim condition meeting the objectives of ship operator. Further to the trim optimization, bulbous bow shape renovation was carried out for off design condition (Fn:0.173) and both of CFD results, one is from an original bulbous bow shape, the other is from a reformed bulbous bow shape by us, are compared each other to identify the concrete reason for the improvement of resistance performance.

Commercial CFD code of the STAR-CCM+ was utilized to evaluate the ship’s resistance performance on a 6,800 TEU container ship. To validate of the effectiveness of Starccm+, the experimental result of the subject hull form is referred and compared with the result from STAR-CCM+.

Form factor prediction method by CFD that is based on extracting form pressure resistance component from difference of two different computational domains is presented. In this study, it is investigated to compare the form factor calculated by CFD with the model test result. This approach allows hull form designer to calculate a form factor corresponding ship’s trim variation by CFD in order to separate total resistance into wave making resistance and viscous resistance for more accurate effective power prediction.
Time Domain Simulation Model for Research Vessel Gunnerus
Authors: Hassani Vahid , Ross Andrew , Selvik Ørjan , Fathi Dariusz , Sprenger Florian , Berg Tor Einar
Published: October 2015

A research vessel (RV) plays an important role in many fields such as oceanography, fisheries and polar research, hydrographic surveys, and oil exploration. It also has a unique function in maritime research and developments. Full-scale sea trials that require vessels, are usually extremely expensive; however, research vessels are more available than other types of ship. This paper presents the results of a time-domain simulation model of R/V Gunnerus, the research vessel of the Norwegian University of Science and Technology (NTNU), using MARINTEK’s vessel simulator (VeSim). VeSim is a time-domain simulator which solves dynamic equations of vessel motions and takes care of seakeeping and manoeuvring problems simultaneously. In addition to a set of captive and PMM tests on a scale model of Gunnerus, full-scale sea trials are carried out in both calm and harsh weather and the proposed simulation model is validated against sea trial data.
Application of Energy Saving Fins on Rudders
Authors: Falkenhorst Arne , Krüger Stefan , Steinbach Christoph Michael
Published: October 2015

Due to rising fuel oil prices in the last decade as well as rising design speeds, it has become common practice to build rudders with twisted leading edges to minimize resistance and cavitation risk. The next step in this development is the application of fins on to the rudder. The aim is to generate a distinct amount of thrust through the fins by retrieving rotational kinetic energy from the propeller slipstream. This paper presents a fast method to design and calculate rudder fins in the propeller slipstream, which has been implemented in the ship design environment E4.

Because of his working principle, the propeller induces velocities to its slipstream. In the usual setup, the rudder is placed behind the propeller to generate higher steering forces caused by the higher inflow speed in the slipstream. In this arrangement, propeller and rudder together are forming a rotor–stator system. The gains of the stator can be maximized by adding fins to the rudder. The main challenge of a fin design is the maximization and prediction of the regained thrust from the propeller slipstream. In order to do this, a steady, three dimensional, direct panel method is used to calculate the flow around the rudder and fin bodies, from which later the pressures and forces are evaluated. A lifting line method is used to predict the inflow velocities caused by the vortex dominated propeller slipstream on each panel. A special focus is on the treatment of the vortex wake, as crossing wake elements can lead to numerical instabilities and a wrong wake alignment produces bad thrust predictions.

For the purpose of rudder design steady computation should be preferred over fully unsteady computation, since only time average integral values are of interest and the degrees of freedom are reduced to the relevant ones. For example, it is not necessary to know the fluctuation of the angle of attack for the basic design of the profile respective the leading edge of the foil, only the mean value is needed.

In the industrial practice, rudder fins are not often used because the calculation is difficult. Until now it is more expensive to design and build the fins than the savings earned by the ship owner. This phenomenon will change in the next years due to better calculations and rising fuel oil prices.
Optimized Hybrid Composite Flexible Pipe for Ultra-Deepwater Applications
Authors: Jha Vineet , Finch David , Dodds Neville , Latto James
Published: October 2015

Different hybrid composite pipe solutions have been proposed and evaluated for use in ultra-deepwater applications. This includes composite and hybrid composite/metallic pipe designs made from both a thermoplastic and thermosetting matrix. Each of these designs target a proportion of the future deep sea market and will require a leveraging of present logistics and infrastructure or new developments for deployment. These design concepts primarily focus on deepwater (hence, a higher collapse load) in combination with higher pressure and/or sour service requirements. A section of this hybrid composite pipe design targets the larger diameter high through-put (low or high pressure) FLNG market.

GE Oil & Gas has proposed hybrid metallic/composite pipelines which use composite layers for both hoop and tensile loads. This paper discusses and compares several different design concepts i.e. bonded composite pressure armor, composite tensile armor and both. Although the use of composite pipe will reduce the overall weight, consideration should be given to the buoyancy versus drag requirements of each composite pipe design. Further, consideration needs to be given to manufacturing, reeling, transportation and installation for each of these different design concepts. Acceptability of these individual designs by the end customer requires detailed FMECA, qualification and testing. This paper therefore compares detailed advantages of each composite pipe design for ultra-deepwater applications, presents the latest developments and compares future applications.

Considerations have been given to development of continuous quality control procedures for the manufacture of these composite pipelines and working prototypes. In addition, the latest results are discussed. The possibilities of defects correction and repair mechanism are also explored. This paper aims to show an appreciation of various composite pipe design concepts and addresses key concerns from both a manufacturing and customer acceptability point of view.
Ship Resistance Validation Using Artificial Ice
Authors: van der Werff Solange , Brouwer Joris , Hagesteijn Gerco
Published: October 2015

In 2013, the first model tests with artificial ice were performed in MARIN’s Concept Basin. A ‘fishbone’ type of channel was made out of rigid polypropylene (PP) particles, surrounded by large rigid PP plates, creating a testing case that is similar to pre-sawn ice conditions in refrigerated model test facilities. A subsequent testing campaign is done in 2014, where the friction between hull and artificial ice particles is further investigated.

Besides measurements of the resistance of the model ship, video images above and under water are used in this study. Results are compared with formulations such as Lindqvist. The knowledge gained with this study is used to improve MARIN’s hydrodynamic multi-body tool aNySIM for simulation studies with ice particles represented by rigid, unbreakable bodies.
In Situ and Real Time X-Ray Computed Tomography for the Micromechanics Based Constitutive Modelling of the Unbonded Flexible Riser
Authors: Pancholi Ketan , Jha Vineet , Dodds Neville , Huo Dehong , Latto James
Published: October 2015

The failure mechanism of the composite flexible riser, comprising a pipe with melt fused carbon fiber tape or pultruded composite rods, is not well understood. As there is change in the configuration of the composite layers and its manufacturing methods, so the bulk material property also changes significantly. To capture the correct material model for global FE analysis, real time x-ray computed tomography was performed while the flexible pipe was being compressed. For developing a constitutive model for the composites, a time series of 3D volume images were analyzed quantifying the local strains responsible for the debonding of the layers and the crack development. These values were then used to understand the inter-layer adhesion leading to correlation between the FE global modelling and experiments capable of capturing the progressive delamination. The resulting global modelling was used to determine the area under compressive loading. The effect of global sea conditions and cumulative damage was noted. A correlation between the global model and experiments can be used to optimize riser performance. This method hopes to capture the overall behavior of flexible pipe under compressive loading.
The Development of a Risk-Based Guideline for the Design of Current and Tidal Turbines
Authors: Macadré Laura-Mae , Paboeuf Stéphane , Dietenbeck Nicolas , le Diraison Stéphane
Published: October 2015

Tidal turbines are emerging technologies offering a great potential by the harnessing of a renewable and predictable resource. However, exploitation at sea comes with significant design, installation, grid connection, and maintenance operations challenges. Consequently, guidelines and standards are required to ensure safety, reliability and quality for these innovative technologies, to support designers and to accelerate the development and commercialisation of the tidal technology. As tidal energy concepts are only at the demonstration stage, only few standards have been published about tidal and current turbines and no dedicated certification procedures have been developed so far.

The aim of this paper is to present a risk-based certification process developed by Bureau Veritas for tidal turbines and published in the Guidance Note NI603 Current and Tidal Turbines. Based on experience accumulated over the past years with tidal turbines technology developers, typical challenges related to the design and installation of tidal devices at sea will be highlighted in this paper. To support tidal turbines designers to take up these challenges, Bureau Veritas provides a decision-making guide gathering 1) recommendations from the existing experience at sea of tidal devices, 2) best practices from related sectors, such as shipping, wind energy or offshore oil & gas, 3) a risk-based approach to consider for the particular requirements of each tidal turbine installation.

In particular for tidal turbines, projects are highly site specific with huge impacts on farm layouts and foundation designs, to name but a few of the issues to be addressed. Paradoxically, the aim of certification societies is to develop rules and tools that can be applicable to a wide range of designs. Consequently, trying not to be design-specific, a proposal of a generic certification process is made in this paper. Existing certification principles from more mature sectors such as wind energy, offshore oil & gas or shipping have been adapted to the specificities of tidal turbines. This paper addresses different certification procedures such as prototype certification, component certification, type certification and project certification. Their respective application and interactions are developed, with a focus on prototype and type certification. In addition, particular attention is paid to the novelty induced by tidal turbines. Consequently, a risk-based guidance is provided to use qualification of new technology for the most innovative parts of the tidal device.
A Novel Data Processing Method for Ice Pressure Statistics
Authors: Neumann Karoline M. , Ehlers Sören , Leira Bernt J. , Kujala Pentti
Published: October 2015

Maritime activities in ice bound areas increase demand for design of structures to withstand ice loads. A cumulative distribution with parameter α as a function of area is published in ISO19906 [1], based on analysis of multiple different discrete full scale rams from Jordaan [2] for application on design loads of discrete impacts. Taylor [3] performs a reanalysis including more full scale data, and taking into account the effect of exposure, presents design parameter curves α-area and x0-area. These are valuable, but are to be applied for design of discrete events, and can only be obtained from discrete event data. The objective of this paper is to describe and demonstrate a data processing method based on semi-continuous ice pressure data that can be applied not only for discrete events, but also for semi-continuous interaction. A finely meshed tactile sensor is applied. Jordaan’s [2] max event method is applied on a new definition of event, based on triggered sensels that are adjacent in time and space. The method is demonstrated on a model scale data set from Aalto University, and example design parameter curves are presented. Applying the developed method on full scale data, the results can be valuable for design of semi-continuous ice loads.
Global Dynamic Performance of Flexible Risers Employing Coupled Analysis
Authors: Drabløs Sigve Orheim , Haakenstad Katharina , Sødahl Nils , Herfjord Kjell , Steinkjer Oddrun
Published: October 2015

Flexible risers are inevitable in the operation of floating production units in intermediate water depths in harsh environments. The operation of flexible pipes under these conditions is challenging, and reliable and accurate analysis of the global performance of risers is vital. The main purpose of this paper is to describe an analysis method for the global performance of flexible risers taking advantages from advanced floater motion modelling and comprehensive modelling of the risers. The analysis scheme has been employed on a semi-submersible platform, operated in harsh environments in the North Sea and all its flexible risers and umbilicals have been analyzed. The platform motions are generated by means of a coupled vessel/slender structure model in which the vessel force model is introduced into a finite element model of the slender structures including the mooring lines and all its flexible risers. In this way all relevant coupling effects from damping, restoring and current loading on the slender structures are consistently included in the platform motion predictions. Subsequently each riser is analyzed in separate models with high element mesh resolution. The platform motions, in terms of low frequency and wave frequency motions obtained from the coupled model, are applied consistently with wave and current loading in the detailed riser model. In the detailed riser models, bending stiffeners are modelled with non-linear material behavior. The diffracted wave field is included in the wave loading of the risers. The stick-slip bending of the flexible pipes have been modelled for a selection of risers and the effect of this on the riser hang off loads and the curvature in the bend stiffener region is discussed. The main responses looked into have been the curvature in the bend stiffener region, the hang off loads and interference between risers and platform pontoons. The riser responses obtained from the coupled analysis scheme performed in the present work is compared to more standard analysis schemes where extreme offsets and transfer functions are used to generate platform motions.
Ice Loads in Dry and Submerged Conditions
Authors: Sopper Regina , Daley Claude , Colbourne Bruce
Published: October 2015

This paper describes a study of the effects of submergence on ice crushing loads. Thirty three small scale indentation tests have been performed on cone-shaped ice samples in dry and submerged conditions using a material testing system (MTS machine) located in a cold room at −7°C. The indenter was a flat aluminum plate at the bottom of a container that was attached to the actuator of the MTS machine. Transparent windows facilitated visual observations and recordings using a high speed camera. In the submerged tests the container was partly filled with salt water. Testing was performed at rates of 1 mm/s and 100 mm/s. The specimens were ice cones with 25 cm in diameter and with 20° and 30° angles. Data recordings comprised time-penetration and time-force histories. Generally higher forces were obtained in submerged tests. Furthermore, the difference between dry and submerged condition was more pronounced at the high indentation rate.
The Influence of the Ship’s Speed and Distance to an Arbitrarily Shaped Bank on Bank Effects
Authors: Lataire Evert , Vantorre Marc , Delefortrie Guillaume
Published: October 2015

A displacement vessel — obviously — displaces a (large) amount of water. In open and deep navigation areas this water can travel almost without any restriction underneath and along the ship’s hull. In restricted and shallow waterways, however, the displaced water is squeezed under and along the hull. These bathymetric restrictions result in increased velocities of the return flow along the hull. The resulting pressure distribution on the hull causes a combination of forces and moments on the vessel. If generated because of asymmetric flow due to the presence of a bank, this combination of forces and moment is known as bank effects.

By far the most comprehensive and systematic experimental research program on bank effects has been carried out in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research – Ghent University) at Flanders Hydraulics Research (FHR) in Antwerp, Belgium. The obtained data set on bank effects consists of more than 14 000 unique model test setups. Different ship models have been tested in a broad range of draft to water depth ratios, forward speeds and propeller actions. The tests were carried out along several bank geometries at different lateral positions between the ship and the installed bank.

The output consists of forces and moments on hull, rudder and propeller as well as vertical ship motions. An analysis of this extensive database has led to an increased insight into the parameters which are relevant for bank effects.

Two important parameters are linked to the relative distance between ship and bank and the ship’s forward speed. The relative position and distance between a ship and an arbitrarily shaped bank is ambiguous. Therefore a definition for a dimensionless distance to the bank will be introduced. In this way the properties of a random cross section are taken into account without exaggerating the bathymetry at a distance far away from the ship or without underestimating the bank shape at close proximity to the ship.

The dimensionless velocity, named the Tuck number (Tu), considers the water depth and blockage, and is based on the velocity relative to the critical speed. The latter is dependent on the cross section (and thus the bank geometry) of the waterway.
Investigation of the Behaviour of the Lateral Buckling Control Method: Reel-Lay Induced Imperfection
Authors: Teigen Martin , Ibrahim Malik
Published: October 2015

Lateral buckling is a design aspect that is frequently considered in the design of subsea pipelines. There are many conventional options for lateral buckling mitigation and control including burial, snake lay, the use of mid-line expansion spools and sleepers. An alternative approach for the control of lateral buckling is to induce permanent imperfections in the pipeline during installation by reel-lay that would encourage a controlled buckling response. Conventional mitigation methods for lateral buckling can require the use of subsea structures or additional installation equipment, whereas the method investigated within this paper removes this need for subsea structures/additional equipment. This method has successfully been practiced for a 26 km long pipeline on Statoil’s Skuld project in the Norwegian Sea. Due to the inherent advantage of this method, it is likely to be of interest to a number of future projects. To date, there is little information publicly available on this method. Therefore, this paper is one of the first to describe the investigation of the lateral buckling response due to reel-lay induced imperfections used as a means of controlling lateral buckling. Consequently, a finite element model has been proposed as part of the pipeline lateral buckling analysis.
Software Analysis Tools for Wave Sensors
Authors: Morrison James , Christie David , Greenwood Charles , Maciver Ruairi , Vogler Arne
Published: October 2015

This paper presents a set of software tools for interrogating and processing time series data. The functionality of this toolset will be demonstrated using data from a specific deployment involving multiple sensors deployed for a specific time period.

The approach was developed initially for Datawell Waverider MKII/MKII buoys [1] and expanded to include data from acoustic devices in this case Nortek AWACs. Tools of this nature are important to address a specific lack of features in the sensor manufacturers own tools. It also helps to develop standard approaches for dealing with anomalous data from sensors.

These software tools build upon an effective modern interpreted programming language in this case Python which has access to high performance low level libraries. This paper demonstrates the use of these tools applied to a sensor network based on the North West coast of Scotland as described in [2,3].

Examples can be seen of computationally complex data being easily calculated for monthly averages. Analysis down to a wave by wave basis will also be demonstrated form the same source dataset. The tools make use of a flexible data structure called a DataFrame which supports mixed data types, hierarchical and time indexing and is also integrated with modern plotting libraries. This allows sub second querying and the ability for dynamic plotting of large datasets.

By using modern compression techniques and file formats it is possible to process datasets which are larger than memory datasets without the need for a traditional relational database.

The software library shall be of use to a wide variety of industry involved in offshore engineering along with any scientists interested in the coastal environment.
Dynamics of a Marine Propulsion System With a Diesel Engine and a Propeller Subject To Waves
Authors: Taskar Bhushan , Yum Kevin Koosup , Pedersen Eilif , Steen Sverre
Published: October 2015

When travelling in waves, the efficiency of the propulsion system is in most cases reduced, due to a variety of different effects. Traditionally, the performance of propeller and engine is analyzed separately. However, there might be important interaction effects, which this paper attempts to explore.

Engine and propeller models have been coupled to obtain realistic response of the propulsion machinery and to observe the effect of interaction between engine and propeller. Experimental wake data have been used in the simulations. The effects of different factors affecting ship propulsion in waves have been noted and their effects have been calculated separately to analyze the influence of each of the factors on ship operation.

A ship travelling in three different wavelengths of three different waveheights has been simulated. Influence of these waves on engine power and fuel efficiency has been studied. This paper is a step towards optimization of installed power through better prediction of sea margin with improved insights into the propulsion performance in waves.
Modelling of Roll Damping Effects for a Fishing Vessel With Forward Speed
Authors: Aarsæther K. G. , Kristiansen D. , Su B. , Lugni C.
Published: October 2015

Vessels in the ocean-going fishing fleet are in general operating in almost all weather conditions. This includes operation in high sea-states which may lead to large amplitude ship motions, depending on the seakeeping characteristics of the vessel. Wave-induced ship motions are important factors for the safety and well-being of fishermen at work. Generally, potential flow theory overpredicts wave-induced roll motion amplitudes for conventional ship hulls. This is due to the presence of viscous damping effects in reality. Large amplitude roll motion of ships can be a real problem if no anti-rolling devices (e.g. bilge keels, anti-rolling tanks or roll-damping fins) are installed, as the roll damping coefficient of a ship is the limiting factor for the resonant roll motion amplitudes. The different components of roll damping for a ship at forward speed were investigated by Ikeda et al. [1], [2] and [3] and updated guidelines for numerical estimation of roll damping have been presented by the International Towing Tank Conference [4], where a component discrete type method for estimation of the damping is suggested. The different roll-damping components of Ikeda et al. has been complemented by skeg damping for smooth hulls [5]. This paper presents comparison between model experiments and the numerical results obtained from the guidelines [4] where the effects of bilge-keels and skeg are isolated.
Tubarão Martelo Field Riser System: Shallow Water Challenging
Authors: Ribeiro Elton J. B. , Tan Zhimin , Hou Yucheng , Zhang Yanqiu , Iwane Andre
Published: October 2015

Currently the oil and gas industry is focusing on challenging deep water projects, particularly in Campos Basin located coast off Brazil. However, there are a lot of prolific reservoirs located in shallow water, which need to be developed and they are located in area very far from the coast, where there aren’t pipelines facilities to export oil production, in this case is necessary to use a floating production unit able to storage produced oil, such as a FPSO. So, the riser system configuration should be able to absorb FPSO’s dynamic response due to wave load and avoid damage at touch down zone, in this case is recommended to use compliant riser configuration, such as Lazy Wave, Tethered Wave or Lazy S.

In addition to, the proposed FPSO for Tubarão Martelo development is a type VLCC (Very Large Crude Carrier) using external turret moored system, which cause large vertical motion at riser connection and it presents large static offset. Also are expected to install 26 risers and umbilicals hanging off on the turret, this large number of risers and umbilicals has driven the main concerns to clashing and clearance requirement since Lazy-S configuration was adopted.

In this paper, some numerical model details and recommendations will be presented, which became a feasible challenging risers system in shallow water. For instance, to solve clashing problem it is strictly recommended for modeling MWA (Mid Water Arch) gutter and bend stiffener at top I-tube interface, this recommendation doesn’t matter in deep water, but for shallow water problem is very important. Also is important to use ballast modules in order to solve clashing problems.