bluuebunny/crossref_metadata_2025 huggingface dataset:
Advancements in Deepwater Drilling Riser Modelling
Authors: Bohan Paul , Lang Donogh
Published: September 2014

Experience with modern ultra-deepwater capable drilling vessels and their associated marine riser tensioner systems has led to increased concerns over tensioner load variations in extreme environments. Modern drilling riser tensioners are complex hydro-pneumatic systems whereby the tension applied at the slip-ring can vary significantly with tensioner stroke in response to vessel heave.

The aforementioned tensioner load variations that occur with modern tensioner systems can have a significant effect on the loads transferred to the wellhead and conductor/casing. This can lead to fatigue concerns at critical locations. The connectors along the conductor and surface casing can be highly susceptible to fatigue if they are located in regions of high bending loads below the mudline.

This paper will give a detailed overview of recent technology advancements that have been incorporated into the latest version of an industry-standard tool for global analysis of drilling risers [1] and that allow these concerns to be addressed. It will focus on two main areas where significant enhancements have been made in tensioner and wellhead & casing modelling. (Note that the version of the software incorporating these capabilities will be made commercially available during 2014.)

The advanced tensioner modelling capability consists of a detailed tensioner model that includes individual hydraulic and pneumatic components of the tensioner system that are fully integrated with a non-linear 3D structural finite element model. This tensioner model is capable of fully capturing all transient behaviour and load variations of real world tensioner systems. This paper will describe in detail this unique modelling capability and its application, including riser recoil analysis.

Additionally, accurate modelling of the wellhead, conductor/casing and the surrounding soil structure is crucial in order to accurately predict bending loads experienced in this region. This includes modelling individual wellhead sections (high pressure housing, low pressure housing and tapered sections) and multi-pipe structures for conductor/casing sections (including cement layers). The advanced soil modelling includes the capability to specify different soil types at different depths. This paper will describe in detail these advanced modelling capabilities.

The detailed tensioner modelling capability represents a highly advanced technical and innovative development and is fundamental to providing a realistic recoil analysis capability. The advanced wellhead and casing modelling allows for accurate prediction of the stresses experienced in this critical region and accurate determination of the fatigue lives of these components. This paper will demonstrate how all of these advanced modelling capabilities can be used to accurately model deepwater drilling risers and provide increased confidence in conducting drilling operations in the harshest of environments.
Outer Cover Damages on Flexible Pipes: Corrosion and Integrity Challenges
Authors: Eriksen Morten , Engelbreth Knut Inge
Published: September 2014

According to published statistics for flexible pipes, penetrating holes in outside covers of flexible pipes is one of the most frequent damage mechanisms. The corrosion and fatigue performances of tensile and pressure armour wires are directly influenced by the fluids in the pipe wall annulus. There are several incidents where cover damages have led to serious pipe failures. In this perspective the best strategy is to avoid cover damage, but for those cases where damage occurs it is essential to have systems in place for early detection, as well as capabilities for repair.

Holes in the outside cover can create a range of different conditions in an annulus depending on location of the hole, configuration of the pipe and service conditions. CO2 driven corrosion in a confined water filled annulus has been investigated extensively and reported by several authors to give very low corrosion rates. However, the environments that armour wires are exposed to in certain parts of an annulus may differ significantly from confined water with CO2. One obvious example is the region around a penetrating hole in the outer cover where there may be repeated ingress of oxygenated seawater or air that mix with CO2 in the annulus. Such environments could cause high corrosion rates that may explain some observed failures.

In many cases it is difficult to quantify the annulus environments precisely and suitable corrosion models have not been established. The consequences are large uncertainties in the prediction of corrosion type and rate, giving challenges for integrity assessment. This paper will identify and discuss unresolved corrosion issues related to outer cover damage linking it to field experience. Needs for developing further knowledge and models will be addressed.

Efficient and reliable methods for repair of outer cover damage that can be mobilized soon are essential for restoring the integrity of pipes with damages to outer covers.
Hydrodynamic Module Coupling in the Offshore Wind Energy Simulation (OWENS) Toolkit
Authors: Fowler Matthew J. , Owens Brian , Bull Diana , Goupee Andrew J. , Hurtado John , Griffith D. Todd , Alves Marco
Published: September 2014

When considering the future of offshore wind energy, developing cost effective methods of harnessing the offshore wind resource represents a significant challenge which must be overcome to make offshore wind a viable option. As the majority of the capital investment in offshore wind is in the form of infrastructure and operation and maintenance costs, reducing these expenditures could greatly reduce the cost of energy (COE) for an offshore wind project. Sandia National Laboratory and its partners (TU Delft, University of Maine, Iowa State, and TPI Composites) believe that vertical axis wind turbines (VAWTs) offer multiple advantages over other rotor configurations considering this new COE breakdown. The unique arrangement of a VAWT allows the heavy generator and related components to be located at the base of the tower as opposed to the top, as is typical of a horizontal axis wind turbine (HAWT). This configuration lowers the topside CG which reduces the platform stability requirements, leading to smaller and cheaper platforms. Additionally this locates high maintenance systems close to the ocean surface thus increasing maintainability. To support this project and the general wind research community, the Offshore Wind ENergy Simulation (OWENS) toolkit is being developed in conjunction with Texas A&M as an open source, modular aero-elastic analysis code with the capability to analyze floating VAWTS. The OWENS toolkit aims to establish a robust and flexible finite element framework and VAWT mesh generation utility, coupled with a modular interface that allows users to integrate easily with existing codes, such as aerodynamic and hydrodynamic codes.

Current efforts to include a hydrodynamic module are focused on coupling WavEC2Wire with OWENS. WavEC2Wire is a wave-to-wire numerical model developed by Marco Alves at the Insituto Superior Tecnico for the analysis of wave energy converter devices. It has been adapted from its original form and restructured for use as a hydrodynamic module capable of providing OWENS with necessary floating platform dynamics. Hence, WavEC2Wire functions as a rigid-body solver designed to calculate the platform motion due to wave loads, moorings, and the influence of the attached VAWT and tower. This paper presents the WavEC2Wire module and details the OWENS coupling method. Additionally, planned improvements in the WavEC2Wire module as well as future development in OWENS are presented.
An Experimental Investigation of Wave Impact Loads on a Slender Horizontal Cylinder
Authors: Haley Joseph F. , Swan Chris , Gibson Richard
Published: September 2014

This paper concerns the difficulties arising in the prediction of the impact loads associated with an extreme wave event. A new set of experimental observations are presented. These concern the impact loads arising on a slender horizontal cylinder located at varying elevations above the still water level. The experimental observations incorporate a wide range of wave forms. In each case, data is provided describing (i) the incident water surface profiles, (ii) the incident fluid velocities and (iii) the load components acting on the cylinder.

Comparisons between the measured data and the classical impact load solutions confirm a number of important departures. In particular, it is shown that as the wave becomes very steep (approaching the breaking limit) the vector sum of the horizontal and vertical velocity components at the water surface may deviate significantly from the normal to the local water surface. In such cases it becomes unclear exactly what direction the impact force acts. The present data suggests that this is, in part, dependent on the rate of inundation of the body. Furthermore, the present results also show that if the direction of the force is correct modelled, the variations in the predicted loading (or slamming) coefficient are much reduced.
How to Detect Local Out-of-Plane Vibrations in Jacket Support Structures for Offshore Wind Turbines
Authors: Schafhirt Sebastian , Hembre John M. , Muskulus Michael
Published: September 2014

There has been an ongoing debate whether local out-of-plane vibrations of braces exist in jacket support structures for wind turbines. The issue has been raised with the sequential analysis of offshore wind turbines, where increased fatigue damage for bracings was observed. Local vibration modes, excited by rotor harmonics, were detected as a reason for it. A methodology to remove global motion of the jacket from the displacements of the central joint in a brace is presented and the amplitude of local out-of-plane displacements is analyzed, using an integrated wind turbine simulation based on a flexible multibody solver. Finally, the impact on fatigue damage is calculated. Results indicate that the extent of local vibrations is much less than previously thought or predicted in other studies.
Dynamic Responses of a Jacket-Type Offshore Wind Turbine Using Decoupled and Coupled Models
Authors: Ong Muk Chen , Bachynski Erin E. , Økland Ole D. , Passano Elizabeth
Published: September 2014

This paper presents numerical studies of the dynamic responses of a jacket-type offshore wind turbine using both decoupled and coupled models. In the decoupled (hydroelastic) model, the wind load is included through time-dependent forces and moments at a single node on the top of the tower. The coupled model is a hydro-servo-aero-elastic representation of the system. The investigated structure is the OC4 (Offshore Code Comparison Collaboration Continuation) jacket foundation supporting the NREL 5-MW wind turbine in a water depth of 50m. Different operational wind and wave loadings at an offshore site with relatively high soil stiffness are investigated. The objective of this study is to evaluate the applicability of the computationally efficient linear decoupled model by comparing with the results obtained from the nonlinear coupled model. Good agreement was obtained in the eigen-frequency analysis, decay tests, and wave-only simulations. In order to obtain good results in the combined wind and wave simulations, two different strategies were applied in the decoupled model, which are 1) Wind loads obtained from the coupled model were applied directly as time-dependent point loads in the decoupled model; and 2) The thrust and torque from an isolated rotor model were used as wind loads on the decoupled model together with a linear aerodynamic damper. It was found that, by applying the thrust force from an isolated rotor model in combination with linear damping, reasonable agreement could be obtained between the decoupled and coupled models in combined wind and wave simulations.
Development and Validation of Panels to Measure Slamming Forces
Authors: Spencer Don , Ryan Ron , Stockwood Blaine , Harris Trevor
Published: September 2014

Ocean conditions have changed over the years, with severe and extreme wave generation occurring more frequently, resulting is larger loads and motions for offshore fixed and floating structures to contend with. It is not known exactly why ocean conditions are growing more severe, but we know that any structure being considered for offshore operations has to be designed to handle larger loads then in the past. Wave slamming, either directly or through run up is an area of growing concern with the offshore industry. During these slamming events the local forces can exceed the strength of the structural plating or the internal frames resulting in structural damage. It is often difficult to predict where these slamming events will occur, therefore large areas are required to be instrumented in order to capture these slamming events during model experimentation. Commercial pressure transducers are typically 5 mm in diameter, which corresponds to full-scale areas of approximately 0.05 m2 or less depended on the scale factor. Thus to cover a large area effectively, a large number of transducers are required. Alternatively a smaller number of larger devices such as force panels with areas of 8 m2 can be used. This area corresponds to the typical area that internal framing would experience slamming loading.

This paper describes the design and development iterations of Oceanic’s model-scale force panels and their applications on modeled offshore structures such as FPSO’s, FLNG’s, and GBS’s. A major advancement in construction of these force panels has been achieved through the use of in-house 3D printing technology to produce complex components.

The paper also presents results from controlled slamming experiments to validate the force panels with respect to piezoelectric pressure sensors and a theoretical slamming model based upon potential flow. Finally, the paper describes the transition from above water installation of the panels to submersion installation and the implementation of the inverse Duhamel analysis to remove the interference due to submerged panel dynamics from the measured response.
CFD Study of Air-Gap and Wave Impact Load on Semisubmersible Under Hurricane Conditions
Authors: Lee Sing-Kwan , Yu Kai , Huang Stanley Chenpey
Published: September 2014

CFD (Computational Fluid Dynamics) simulations of airgap and wave impact load on a semisubmersible under extreme wave conditions are performed in this study. Unlike the common practice, in which environmental waves are modeled as regular waves, a random wave series based on a JONSWAP spectrum for a 100-year return wave in the Gulf of Mexico is used to interact with a moored semisubmersible to simulate a more realistic environment condition. Wave run-up and impact loads on a moored semisubmersible due to both regular and random waves are computed and compared to investigate the influence of these different extreme waves on motion and impact load.
Spar Platform Installation: Tank Flooding Simulation
Authors: Medellin Abel , Arango-Turner Michelle , Fuhr Curtis
Published: September 2014

Spars are towed to installation site horizontally and upended by progressive flooding of tanks. It is common practice to perform a dynamic time domain simulation for a self upending classic spar to determine hydrostatic pressures on compartments. There are many different flooding scenarios that create challenges in modeling and simulation during the design phase.

In one particular scenario, the spar upending is initiated by opening valves that allow water to flood into the skirt tank. The skirt tank will progressively fill, based on the differential hydrostatic pressure at valves, and cause the spar to upend. Flooding into keel tanks will commence once respective openings become submerged. Several openings from the skirt tank into the keel tanks reduce the differential pressure experienced in the keel tanks during upending.

Simulation of the transfer of water between tanks cannot be modeled with ease using the standard tank flooding options available within the software suite. This particular compartment flooding problem is solved by utilizing a scheme in which the time domain simulation was performed iteratively for a specified time interval. For every iteration the amount of water transferred between the skirt and keel tanks are calculated. The amount of water transferred is calculated using a custom modeling technique.

The openings from the skirt tank into the keel tanks are not modeled as a typical hole or valve into a compartment, but the location of these holes are modeled. The amount of water flowing through these openings is determined by the water level in the skirt tank, friction through the opening, and pressure inside the keel tanks.

This paper will describe in detail the scheme developed, the tank modeling requirements, and the results obtained.
Best Practices for Minimizing Mooring Failures at the Fairlead
Authors: Miller Jonathon D. , Kärrsten Gennine R. , Haveman Curt E.
Published: September 2014

Although preventive maintenance is not a new concept when dealing with mooring systems, experience shows that the implementation is not always successful. As important as new technologies are in improving mooring integrity, it is equally important to ensure that well-established best practices remain in place. As the industry approaches a period where extending service life of floating structures is desirable, but the existing mooring system has reached the twilight of its service life, the need for properly maintaining the mooring system is more acute. With time on their side, the prudent operator can implement small regular steps to extend mooring system service life. This paper presents methodologies to maximize design life by highlighting design and operational best practices, maintenance and monitoring, and identifying common reasons why these best practices are not implemented.
Port Placement Theory in Consideration of Geographical Characteristics and Disaster Risks in Case of Ocean Space Utilization
Authors: Takahashi Koji , Kasugai Yasuo , Fukuda Isao
Published: September 2014

In case of ocean space utilization, the factors which have to be taken into consideration in order to form an international basic container route are geographical factors which are the position on a global scale, the economic scale of port hinterland, the ocean climatic condition for setting the route etc. as well as factors from the viewpoint of transport such as the volume of container cargo and both size of container ships and container terminals. It is important to consider these geographical factors not only in order to study the port placement from the global point of view but also to devise the port policy. Although there are many studies on factors from the viewpoint of transport, there is almost no study on these geographical factors. Then, the authors made a new simulation model and analyzed these geographical factors of the international container ports in all parts of the world. As a result of analysis, the authors got the conclusion that there were three port placement patterns. The first type is ‘the Continent Base Port Type’, which it is located in the continent and has the large economic hinterland. Typical ports of this type are Antwerp, LA, LB and Shanghai. The second type is ‘the Ocean Base Port Type’, which is located in the ocean space where geographical predominance is high. This type forms route hubs. Typical ports of this type are Singapore, Malta and Kaohsiung. The third type is ‘the Tight Hinterland Port Type’, which is located in an island and has the tight economic hinterland where the economic activities density is very high. This type has characteristics that the distance between the ports is short and there are a lot of numbers of ports, which is unique and special in the world. Japan’s ports are classified in the third type. Furthermore, Japan has a characteristic that there are many large-scale earthquakes and has to consider earthquake measures to reduce disaster risks. The authors will suggest the most suitable port placement theory in consideration of these characteristics in case of ocean space utilization.
Dynamic Responses of a Steel Cylinder in the Process of Lifting by a Floating Crane in Waves
Authors: Chen Keqiang , Zhang Hong , Niu Zhao , Zhou Lilan , He Wei , Wang Jiamei
Published: September 2014

Dynamic responses of a heavy cycloidal object hanged by a large floating crane in the process of immersing into waves were studied experimentally and numerically in this paper. A floating crane with displacement of 14000t was selected as the reference. A model with the scale of 1:20 was conducted in a towing tank. The movement responses and forces of the heavy cycloidal object in the process of immersing in waves were researched.

Ocean engineering construction is always affected significantly by waves, so the selection of a shield to attenuate incoming waves is an important aspect for ocean engineering construction. The sea condition in our project is 3-state sea condition; it’s not an acceptable condition for real construction considering safety of crews and the ability of equipments. So an effective floating breakwater validated experimentally in a towing tank in our project was proposed as effective shields. The steel cylinder lifted by a floating crane in the process of water-entering was experimented, the movements of the steel cylinder and the subjected forces of the hoist were recorded; the effects of different shields on the responses of steel cylinder with different depth in water were studied. Numerical simulations of the motion of steel cylinder subjected to waves in the process of immersing were conducted to illustrate the effects of headings. The basis of model design, model-making and measurement methods are also introduced in this paper. The results are translated into full scale results which will be the basis for safety construction of ocean engineering and measurement proposed for accurate positioning and installation of the steel cylinder.
A Searching Technique for Obstacle-Avoidance of Autonomous Underwater Vehicles by Using the Self-Tuning Fuzzy Controller
Authors: Lin Yu Hsien , Fang Ming Chung , Chang Hui Hua
Published: September 2014

This study develops a heuristic searching technique for obstacle-avoidance of autonomous underwater vehicles (AUVs) in varying ocean environments by using the self-tuning fuzzy controller. The corresponding hydrodynamic coefficients for the AUV are obtained by the test of Planar Motion Mechanism (PMM), which serves as the important data inputs for the control system. Subsequently, the self-tuning fuzzy controller would be adopted to command the propulsion of AUVs. The function of obstacle-avoidance is based on the underwater image detection method with the BK triangle sub-product of fuzzy relations which can evaluate the safety and remoteness of the candidate routes and the successive optimal strategic routing can then be selected. In the present simulations, the current effect is used to investigate the maneuvering performance of obstacle-avoidance. Eventually, the present study indicates that the self-tuning fuzzy controller, combined with the image detection technique based on BK triangle sub-product of fuzzy relations, is verified to be a useful searching technique for obstacle-avoidance of AUVs in depth variation.
Which Sea States Are Dimensioning for Container Vessels When Whipping Is Included?
Authors: Storhaug Gaute
Published: September 2014

Four container vessels have broken in two during the last four decades. There may not be one single cause explaining these severe accidents. They all broke in moderate storms, but they did not break in extreme storms in terms of extreme wave heights. How could this happen? This paper addresses one possible contributing effect to all of these accidents, i.e. whipping, and how whipping contribute in different sea states.

Whipping, as a sudden hull girder vibration caused by bow flare impacts, can contribute significantly to increase the vertical hull girder bending moments of container vessels, which have high design speeds and pronounced bow flare. Model tests have been carried out based on modern container ship designs covering one Panamax vessel, one Post Panamax vessel and one Ultra Large Container Ship. The tests have been carried out primarily in head seas. The whipping contribution depends on the vessel speed, and the tests have been carried out using realistic speed in each sea state. Lower sea states are more frequent than higher sea states, and lower sea states are associated with higher speeds. Does this speed dependence give other dimensioning sea states when whipping is considered?

For all three vessel designs, it is not the highest sea states, which define the dimensioning wave moments when whipping is included. Actually, realistic encountered storms can produce the dimensioning wave bending with whipping. These sea states differ considerably from the sea states, which produce the maximum wave moment without whipping. It is also demonstrated how different trades affect the dimensioning wave bending with whipping.

The industry seems most concerned about the effect of whipping for the largest vessels. These model tests demonstrate that the dimensioning moment with whipping for the largest vessel is not the main concern. The tests suggest that the bow flare angle is most important, and these may be high for Post Panamax vessels. The speed is well known to be important, while size in terms of length is not particularly important from these tests.
Evanescent Wave Reduction Using a Segmented Wavemaker in a Two Dimensional Wave Tank
Authors: Keaney Iain , Costello Ronan , Ringwood John V.
Published: September 2014

The concept of a segmented wavemaker, in a two dimensional tank, has been investigated analytically to see if it can reduce the effect of parasitic evanescent waves in a wave tank. Evanescent waves can contaminate test areas in tanks leading to unreliable results, but are typically avoided by establishing the test area two to three times the water depth away from the wavemaker. This space requirement can be quite restrictive in terms of the necessary tank size and, with the increasing interest in off-shore renewable energy, many technology developers may not be able to afford a workspace large enough to accommodate a long tank. Previously, flexible wavemakers have been designed to tackle the problem and, in some cases have proven very effective in eliminating evanescent waves at the wavemaker’s “tuned” frequency. However, flexible wavemakers have been shown to have little benefit in modeling panchromatic seas. Discussed here is the linear potential theory of a segmented wavemaker designed to reduce the evanescent waves in a tank over a large frequency range. Each segment in the segmented wavemaker is programmed with an individual stroke, allowing the system to best approximate the horizontal displacement of the fluid over the depth of the water in a naturally occurring wave. A comparison of the influence of evanescent waves created by segmented wavemakers, piston and hinged paddle wavemakers, on the free surface elevation is presented.
Modeling of Hydraulic Fracture Network Propagation in Shale Gas Reservoirs
Authors: Ahn Chong Hyun , Dilmore Robert , Wang John Yilin
Published: September 2014

The most effective method for stimulating shale gas reservoirs is horizontal drilling with successful multi-stage hydraulic fracture treatments. Recent fracture diagnostic technologies have shown that complex fracture networks are commonly created in the field. The interaction between preexisting natural fractures and the propagating hydraulic fracture is a critical factor affecting the complex fracture network. However, many existing numerical models simulate only planar hydraulic fractures without considering the pre-existing fractures in the formation. The shale formations already contain a large number of natural fractures, so an accurate fracture propagation model needs to be developed to optimize the fracturing process.

In this paper, we first understood the interaction between hydraulic and natural fractures. We then developed a new, coupled numerical model that integrates dynamic fracture propagation, reservoir flow simulation, and the interactions between hydraulic fractures and pre-existing natural fractures. By using the developed model, we conducted parametric studies to quantify the effects of rock toughness, stress anisotropy, and natural fracture spacing on the geometry and conductivities of the hydraulic fracture network. Lastly, we introduced new parmeters Fracture Network Index (FNI) and Width Anistropy (Wani) which may describe the characteristics of the fracture network in shale gas reservoirs. This new knowledge helps one understand and optimize the stimulation of shale gas reservoirs.
Experimental Assessment of the Offshore Launching Operation of a Jack-Up Unit
Authors: Rodríguez Claudio A. , Esperança Paulo T. T. , Moura Mário , Raigorodsky Jacques
Published: September 2014

Recently, an experimental campaign was carried out to assess the feasibility of the launching operation of two jack-up units using a barge as the launching platform. This experimental study was divided in four stages. In stages 1 to 3, a series of preliminary model tests were performed in order to provide scientific understanding of the mechanics of the operation, and investigate systematically the influence of launching parameters. The experimental approach developed for testing this operation and the results of the preliminary launching tests have been discussed in detail in a previous paper [1]. Based on the analyses of the experimental results of stages 1 to 3 and, the results of numerical simulation tools, in stage 4, a final launching condition was designed and a new set of model tests were specified to check the safety of the operation. This paper presents the results and analyses of the experimental tests in stage 4. The conditions tested in this stage covered the expected real launching condition and possible deviations in some launch parameters. The tests results include the 6-DOF motions and trajectories of the launched jack-up and the launch barge, and the reaction forces on the barge rocker arms. Later on, the success of the launching operations of P-59 and P-60 jack-up units confirmed the experimental investigation results and the feasibility of this novel launching procedure. Furthermore, it can be concluded that the experimental approach efficiently served as a tool for the assessment of high risk operations.
Improving Resource Assessment of Wave Power Based on Spectral Wave Model
Authors: Waseda Takuji , Asaumi Sho , Kiyomatsu Keiji
Published: September 2014

Epistemic uncertainties of wave power estimation based on spectral wave model were assessed utilizing the community wave model WW3 of NOAA. A four tiered nested model was constructed covering the Pacific Ocean, the sea around Japan, the North-Eastern Japan and Kamaishi regional model at 100km, 10km, 1km and 100m resolutions respectively. The sensitivity of the model output to four wind products (NCEP-GFS, NCEP-CFSR, GSM/JMA, ERA-interim/ECWMF) was tested; the wave model outputs as well as wind products were validated against observations of NDBC buoys, JKEO/JAMSTEC buoy, TAO array and NOWPHAS buoy along the north-eastern Japan. The differences of the estimations using four wind products were relatively small whereas model errors were spatially inhomogeneous. The dependence on grid-resolution was relatively small at depth 100m or so. On the other hand, the modeled significant wave period had a large bias from the observation because of the inconsistency in the spectral moment used to estimate the significant wave period. The energy period (T-1,0) was 5% larger than the period from WW3 (T-0.5,0) and 20% larger than the period from NDBC (T0,2). The difference of wave period, dependent on the spectral shape and location, are often overlooked despite their significant impact on the resource estimate.
Effects of Passing Ship With a Drift Angle on a Moored Ship
Authors: Zhou Minggui , Roelvink Dano , Zou Zaojian , van Wijhe Herm Jan
Published: September 2014

When a ship sailing at low speed passes a moored ship with a drift angle due to wind effect, the flow field around the ships is very different to the flow field without a drift angle and will cause larger hydrodynamic forces on the moored ship, compared with those without a drift angle. In this paper, a flow model in XBeach is applied to study the effects of a passing ship at low speed with various drift angles on the moored ship. This method is based on the non-hydrostatic shallow water equations. Simulations are carried out for a 12500 TEU container ship passing a moored Panamax ship by using XBeach. The water level depression, return current and hydrodynamic forces on the moored ship are obtained and compared with the measurement data. Then the results at positive and negative drift angles are compared with the results at zero drift angle, respectively. The influence of the drift angle on the passing ship effects is analyzed and the most serious situation for the moored ship, when the passing ship has different drift angles, is indicated. Finally, conclusions concerning the effects of a passing ship with a drift angle on a moored ship are drawn.
In-Line and Cross-Flow Interaction of a Flexible Beam Subjected to Vortex Induced Vibrations
Authors: Wu Jie , Lie Halvor , Larsen Carl M. , Liapis Stergios
Published: September 2014

It has long been known that in-line (IL) response will influence cross-flow (CF) vortex shedding forces and vice versa. However, empirical codes for prediction of vortex induced vibrations (VIV) of slender marine structures have so far been limited to handle CF or IL response separately without taking into account the interaction between the two response modes. The motion phase angle between IL and CF displacement is a key parameter to be included in the empirical codes in order to model such interaction. The present study uses the data from Shell’s High mode VIV experiments that were performed at the MARINTEK Offshore Basin in March 2011. This extensive test program provides a rich dataset for measuring the motion phase angle and hydrodynamic force coefficients under different flow conditions. It is found that the energy transfer from the fluid to the pipe is related to counter-clockwise trajectories inside the excitation region; while clockwise trajectories are associated with hydrodynamic damping forces. The influence of the travelling wave behavior on motion phase angle and hydrodynamic force coefficients are also studied. It was found that the spatial variation of the motion phase angle of the beam is different when travelling waves dominate the response.
Influence of Short Polypropylene Fibers on the Toughness of High Performance Cement Slurries
Authors: Barghigiani Thayane Martins , Toledo Filho Romildo Dias , Balthar Vivian K. C. B. L. M. , Miranda Cristiane R. , Velasco Reila V.
Published: September 2014

In oil wells, one of the goals of the cement sheath is the hydraulic seal. Generally, cement pastes, which are adopted in cementing operations, exhibit brittle fracture when subjected to tensile stresses. This behavior can compromise the hydraulic seal promoted through the sheath. One way to mitigate this problem is the use of slurries with more deformability. In this context, this work aims the determination of the toughness of high performance cement slurries reinforced by different volume fractions (0.50% and 0.75%) of short polypropylene fibers (6mm long). The influence of fiber addition in the rheological behavior, free fluid, density, stability and unconfined compression of the slurries was also determined. The obtained results indicated an increase in the yield strength and a reduction in the spreading of the reference mix with the increase of the fiber volume fraction. The free fluid, density and stability behavior of the reinforced slurries were similar to that of the control mix. An expressive change in the fracture behavior of the brittle matrix was observed in both mechanical tests carried out. Under uniaxial compression loads, although the ascending branch of the stress-strain curve did not show expressive differences with the fiber reinforcement (only minor modifications in the peak load), the descending branches were significantly modified with the reinforced mixes presenting a smooth post-cracking behavior. The greatest benefit provided by the fibers was observed, however, in the bending tests. Both, the maximum post-cracking strength and bending toughness, were significantly augmented with the increase of the fiber volume fraction.
An Analytical Elasto-Plastic Analysis for Stability of Axisymmetric Wellbore
Authors: Chen Shengli , Abousleiman Younane , Abass Hazim
Published: September 2014

In this paper, a general shear strain hardening and softening Drucker-Prager model based on the existing triaxial compression test results has been introduced to model the rock behaviour which captures well the mechanical characteristic of typical soft rock formations. This elastoplastic model is then adopted to develop a rigorous analytical solution for the drained wellbore drilling problem subjected to in-plane isotropic stress field, and to simulate the borehole collapse failure. It is found that the wellbore boundary value problem can be reduced to solving a system of first order ordinary differential equations in the plastic zone, with the radial, tangential, and vertical stresses as well as the volumetric strain and plastic shear strain being the five basic unknowns. The illustration numerical example shows the distributions of stress components and volumetric strain around the borehole, in addition to the evolving plastic deviatoic strain and stress path for a rock point at the borehole surface due to the wellbore drilling. The critical mud pressures necessary to prevent borehole collapse, predicted by the elastoplastic analysis based on different wellbore instability criteria, are compared with the value corresponding to the elastic theory, which are found to be considerably lower.
Rheology and Hydration of Cementitious Slurries
Authors: Hansen Will , Koenders Eduardus , Liu Zhichao
Published: September 2014

Predicting temperature effects on rheology and hydration of cementitious slurries considered for oil-well cement applications is important as temperature can vary significantly in a bore-well. During the plastic stage the fluid properties (yield and plastic viscosity) are investigated using a rheometer, while isothermal calorimetry is used to evaluate setting characteristics and early-age (0–7 days) heat of hydration. In this paper, experimental results at 3 different temperatures show that a 50/50 blend of Type I portland cement and slag cement at a 0.45 water-cementitious ratio has similar rheological and hydration properties as the reference system (Type I portland cement paste). The rheological properties were found to follow a two-parameter Bingham model, and temperature effects can be accounted for by an Arrhenius model. The effect of temperature on hydration rate can be predicted by a maturity function, which also is based on the Arrhenius rate model, where the apparent activation energy is a measure of temperature sensitivity.
On Variability of Mean Wave Direction During Severe Storms
Authors: Laface Valentina , Arena Felice , Guedes Soares Carlos
Published: September 2014

The paper deals with the directional analysis of severe storms in some European locations, in the Atlantic Ocean and North Sea. The analysis is carried out by considering significant wave height and wave direction time series, from the HIPOCAS project database. At each considered location, all storms in the data set are identified. Then, for each storm, variability of direction during sea states is investigated. The results of this analysis show how direction during storms varies within well-defined sectors identified from the main directions from which the strongest storms occur plus or minus a certain angle Δϑ, and from one or more secondary sectors. The variation of direction during storms is evaluated in terms of standard deviation of direction, either by considering all sea states during storm, or only sea states during the part of the storm above a fixed threshold h of significant wave height. The results show that standard deviation of direction decreases as the threshold h increases and it is due to the fact that variability of direction near the storm peak is smaller than in the full storm.
A Coupled SPH-Spectral Method for the Simulation of Wave Train Impacts on a FPSO
Authors: Oger G. , Le Touzé D. , Ducrozet G. , Candelier J. , Guilcher P.-M.
Published: September 2014

In order to help in achieving a correct design of structures subjected to wave impacts, CFD tools with a sufficient accuracy should be developed. But nowadays, modelling accurately both wave propagations and the resulting impact of a wave train on a complex geometry is still challenging. This paper deals with the introduction of a weak coupling between a Spectral method and Smoothed Particle Hydrodynamics (SPH), used as complementary techniques for modelling respectively wave propagation and high-dynamic impact of a wave train on a complex-shaped floating body. Comparisons with experiments are provided as a validation of these preliminary developments.
Quantitative Risk Assessment (QRA) of an Exploratory Drilling Oil Spill in Deepwater Gulf of Mexico
Authors: Zulqarnain Muhammad , Tyagi Mayank
Published: September 2014

Major offshore accidents such as Macondo well incident highlight one of the possible failure modes and subsequent disasters when an offshore engineering project could go wrong. Such events can potentially happen during any phase of an offshore well’s life — starting from the exploratory drilling phase to the final phase of plug and abandonment. Major factors that significantly contribute in defining such accident scenarios are the geological and operational complexities, equipment reliability, human factors, geographical/economy location, and environmental conditions. The path taken by the reservoir fluids to reach the sea floor is also an important factor in determining the worst case discharge rates. It is expected that the environmental risks from an oil/gas spill would also be function of the type of hydrocarbons released and duration of the spill.

A representative Neogene well is studied for quantitative risk assessment (QRA) for spill in exploratory phase from the Mississippi Canyon in the Gulf of Mexico with a water depth of 3,000ft and total vertical depth of 16,726 ft and the representative reservoir properties for this area are selected from the literature. Due to the large variation of reservoir properties, lognormal distributions have been assumed for some of the reservoir properties and from the Monte Carlo simulations P10, P50 and P90 values are estimated. Based on P50 and P90 values, the worst case discharge rates are calculated using a commercially available multiphase flow simulator with black oil model. Based on historical trends, release of hydrocarbons during blowouts are simulated for the following circumstances: seabed and topside releases, restricted and unrestricted flow through BOP, flow with drill pipe inside the wellbore and open hole flow without drill pipe and flow from the reservoir when it is either fully or partially penetrated. To incorporate the technological improvements and study their effects on the reduction of the overall risk associated with deepwater drilling activity, two cases are considered and compared to each other. First case is based on the historical data and the second case is a modified version of the first case by incorporating some of the recent technological improvements and newly built oil spill response systems e.g. capping stacks. The historical kick statistics and the equipment reliability data available in the literature is used to analyze various scenarios and corresponding flow rates. Risk is analyzed using the failure probability and consequence analysis and is presented in the form of a risk matrix for the different case studied and for the overall drilling activity as well.
The Dynamic Response of Floating Foundation for 1.5MW Wind Turbine in 30m Water Depth
Authors: Tang Yougang , Wang Han , Li Jiawen , Wang Bin , Li Wei
Published: September 2014

The floating foundation is designed to support a 1.5MW wind turbine in 30m water depth. Considering the viscous damping of foundation and heave plates, the amplitude-frequency responses characteristics of the foundation are studied. Taking the elastic effect of blades and tower, the classic quasi-steady blade-element/ momentum (BEM) theory is used to calculate the aerodynamic elastic loads. Coupled dynamic model of turbine-foundation-mooring lines is built to calculate the motion response of floating foundation under Kaimal wind spectrum and regular wave by using the FAST codes. The model experiment is carried out to test damping characteristics and natural motion behaviors of wind turbine system, as well as the motion responses considering joint of wind and wave and only with wave. It is shown that the wind turbine system can avoid the harmonic vibration by the wind and wave, in addition, the floating foundation heave is induced by wave, while surge motion is induced by wind, and the action of wind and wave is of significance for pitch.
An Experimental and Computational Development of a Benchmark Solution for the Validation of Numerical Wave Tanks
Authors: Bøckmann Arne , Pâkozdi Csaba , Kristiansen Trygve , Jang Hyunchul , Kim Jang
Published: September 2014

A joint effort between MARINTEK, DNV GL and Technip has been made to develop a set of benchmark solutions for the validation of numerical wave tanks. High-fidelity measurements of the wave field around a vertical circular cylinder from a scaled model test have been selected as the benchmark cases. A reference numerical wave tank based on a commercial CFD software and the Euler-Overlay Method as far-field closure has been validated by grid convergence test and comparison with the model test data. The validated numerical solution can be used as a benchmark solution to validate other numerical wave tanks.