bluuebunny/crossref_metadata_2025_split huggingface dataset:
Equilibrium Scour Prediction for Uniform and Non-Uniform Cylindrical Structures Under Clear Water Conditions
Authors: Tavouktsoglou Nicholas S. , Harris John M. , Simons Richard R. , Whitehouse Richard J. S. 
Published: October 2016

Offshore Gravity Base Foundations (GBFs) are often designed with non-uniform cylindrical geometries. Such structures interact with the local hydrodynamics which amplify the adverse dynamic pressure gradient, which is responsible for all flow and scour phenomena including the bed shear stress amplification. In this study a method for predicting the effect non-uniform cylindrical structure geometries have on local scour around offshore structures under the forcing of a unidirectional current is presented. The interaction of the flow field with the sediment around these complex structures is described in terms of non-dimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights in the influence a form of the Euler number has on the equilibrium scour around uniform and non-uniform cylindrical structures. Here the Euler number is defined as the depth averaged pressure gradient (calculated using potential flow theory) divided by the product of the square of mean flow velocity and the fluid density. The insights are confirmed through a series of experiments where the equilibrium scour was monitored for different types of structures and flow conditions.
The results of this study show that the Euler number is a more appropriate parameter for describing the scour potential of a structure compared to using the equivalent pile diameter. The experimental data show that an increasing Euler number yields an increase in the non-dimensional equilibrium scour. The results of this study also suggest that an increase in the water depth yields a decrease in the equilibrium scour depth for the conical, cylindrical base structures and truncated cylinders and an increase in the equilibrium scour depth for the uniform cylinders which can also be explained in terms of changes in the Euler number. Finally, the Buckingham π theorem in conjunction with the experimental data was used to derive a simple shape correction factor that could be used to determine the scour depth of a non-uniform cylindrical structure based on the equilibrium scour produced for the same flow conditions by a uniform cylinder.
Effect of Acidizing Treatments on the Fatigue Crack Growth Behavior of C-Mn Line Pipe Steels
Authors: Batra Apurva , Bowman Jonathan , Yu Weiwei , Thodla Ramgopal , Holtam Colum , Gerst Brandon 
Published: October 2016

Acidizing treatments are typically performed intermittently during the life of a well. However, more recently there has been a desire to perform an increased number of acidizing treatments in order to improve production. The acidizing treatments typically involve highly corrosive acids, such as hydrofluoric (HF), hydrochloric (HCl) and acetic acid, which are known to cause significant corrosion, but could also lead to environmentally assisted fatigue and fracture. A study was performed to evaluate the effect of acidizing treatments on the fatigue behavior of welded C-Mn line pipe steels. This paper describes the results of fatigue crack growth rate (FCGR) tests on as-welded (i.e. unstrained) pipe.
FCGR tests were conducted at room temperature (RT) in three different acid conditions: fresh acid with corrosion inhibitor, spent acid with corrosion inhibitor and spent acid without corrosion inhibitor. Frequency scan FCGR tests were performed on compact tension (CT) specimens notched in the parent pipe (PP), heat affected zone (HAZ) and weld centerline (WCL). The FCGRs in all three environments were higher than in air and exhibited a frequency dependence. Tests in fresh acid with inhibitor exhibited plateau FCGR values around 20–30 times higher than in air. Tests in spent acid with inhibitor exhibited a strong frequency dependence with plateau FCGR values approximately 80–100 times higher than in air. In spent acid without inhibitor, the plateau FCGR was around 20 times higher than in air, however at the lowest frequencies the FCGR decreased, most likely due to crack closure/blunting effects. This behavior is consistent with the higher corrosion rate in this uninhibited environment.
The role of corrosion products in causing crack closure/blunting was further evidenced in tests performed at elevated temperature (165°F / 74°C), where the FCGR at 1Hz was significantly higher than at RT. The plateau FCGR in fresh acid and spent acid with inhibitor was approximately 40–50 times higher than in air, but the FCGR decreased at lower frequency. This is similarly believed to be due to the higher corrosion rates at elevated temperature causing crack closure/blunting. The FCGR in spent acid without inhibitor at 165°F (74°C) was high initially at 1Hz but then decreased sharply, which is consistent with the highest corrosion rates expected at elevated temperature and in the absence of corrosion inhibitor.
Paris curve FCGR tests were subsequently conducted at 0.1Hz. Tests were performed in the worst case combinations of microstructure/environment/temperature identified from the frequency scan tests.
Effect of Sour Acidizing Treatments on the Fatigue Crack Growth and Fracture Toughness Behavior of C-Mn Line Pipe Steels
Authors: Yu Weiwei , Bowman Jonathan , Batra Apurva , Thodla Ramgopal , Holtam Colum , Gerst Brandon 
Published: October 2016

Acidizing treatments are typically performed intermittently during the life of a well. However, more recently there has been a desire to perform an increased number of acidizing treatments in order to improve production. The acidizing treatments typically involve highly corrosive acids, such as hydrofluoric (HF), hydrochloric (HCl) and acetic acid, which are known to cause significant corrosion. In the presence of hydrogen sulfide (H2S), these acidizing treatments could cause environmentally assisted fatigue and fracture (i.e. increased fatigue crack growth rates and reduced fracture toughness).
A test program is underway to evaluate and quantify the effect of sour acidizing treatments on the fatigue and fracture behavior of welded C-Mn line pipe steels. This paper describes the preliminary findings from fatigue crack growth rate (FCGR) and fracture toughness (FT) tests on as-welded (i.e. unstrained) pipe.
All tests were conducted at room temperature (RT) using compact tension (CT) specimens notched in the parent pipe (PP). Frequency scan FCGR tests were performed in the following sour acid conditions: simulated production environment (PE), spent acid without inhibitor and spent acid with residual corrosion inhibitor. The PE consisted of a simulated brine with pH = 4.5 and partial pressure of H2S (pH2S) = 0.21psia. FCGRs in the sour PE were of the order of 20 times faster than in air. The pH2S was the same for the tests in spent acid environments, but the pH was lower (approximately 3.5). As would be expected, the FCGRs were much higher in the low pH environment. The highest FCGRs were observed in the inhibited sour spent acid environment and were up to 100 times faster than in air.
Sour FT tests were also conducted in the PE and in spent acid with and without inhibitor. In all cases, the measured FT values were significantly lower than in air. The test in PE exhibited higher FT than in the sour acidizing environment. The lowest FT values were observed in spent acid with inhibitor.
Future work will investigate the effect of reeling on the fatigue and FT performance of pipe girth welds in sour acidizing environments.
Corrosion Fatigue Behavior of Mooring Chain Steel in Seawater
Authors: Arredondo Alberto , Fernández Jonathan , Silveira Elena , Arana José Luís 
Published: October 2016

With a majority of the reported chain failures related to fatigue, this phenomenon is one of the main topics to be studied as part of Mooring Integrity Management. Present fatigue design is mainly based on fatigue curves for chains under tension-tension loads in seawater. However, the applicability of these curves for different loading modes and specific environments remains unclear.
This paper studies the fatigue behavior of the material used on chains as it builds the baseline for the performance of these mooring components. It includes uniaxial fatigue tests that were undertaken on R4 and R5 steel grades obtained from actual chains after all their manufacturing steps. Samples were not only tested in air and in synthetic seawater but different corrosion related parameters were also studied: frequency, temperature and cathodic protection.
From the results of these tests, separated SN curves were obtained. Subsequently, these curves were analyzed and compared against present recommended design curves for material. Fractographic examination was undertaken to assess the effect of corrosion and cathodic protection and comparison between material and component response was also addressed. Results showed the strong synergy between corrosion and fatigue. Also, the improvement from fatigue design curves to actual response of the materials was quantified.
Model of Transit Transport in Arctic Based on Graph Algorithms
Authors: Zvyagin Petr , Voitkunskaia Anna 
Published: October 2016

Transportation in Arctic seas is connected with variability of routes. Availability of those routes is depending on current environmental conditions. In the paper the algorithm for navigation system, which is intended to advice captain the most economically effective and less risky route with the presence of ice chart, is proposed.
Smart navigation system for Arctic seas has specific: shortest ways can occur to be impassable or too risky. More long routes through free waters can finally take less fuel comparing to shorter, but covered with ice. Thus, economical profitability of operating in Arctic seas depends on effectiveness of route choosing.
To make estimations about most effective route and its length, the method based on graph algorithms is presented in this paper. The ice chart is covered by the graph, which can have form of grid, with neighbor nodes connected by edges. In general, multiple parameters can be assigned to each edge — length, maximal ice thickness on the way, risk, etc. In this paper two separate cost functions are considered: first is responsible for travel expenses, and the second is responsible for ice passability on the route.
To find most economically efficient route with minimal possible ice thickness on the way the method with graph modification and Dijkstra algorithm was used. This route provides Pareto-optimal solution for reduced version of the problem.
The software, which implements the method, was built. The example of searching for least expensive and Pareto-optimal route is provided. Results are discussed.
Dynamic and Static Sagging Characterization and Performances of Four Oil Based Muds
Authors: Belayneh Mesfin , Aadnøy Bernt S. , Thomas Sharman 
Published: October 2016

This paper presents the barite sagging phenomenon of four OBM systems having the same density, but different rheology properties. The investigations of barite sagging is based on dynamic sagging and viscoelasticity testing. The viscoelastic properties related to gel formation of the drilling fluids were investigated under amplitude and frequency sweeps.
The study also tries to correlate the results obtained from dynamic sag with the dynamic viscoelastic properties of the drilling fluid and standard API rheology parameters.
The results show that as the oil water ratio increases the drilling fluid rheology parameters such as lower shear yield stress (LSYS), yield stress (YS) and plastic viscosity (PV) parameters also increases. In addition, the viscoelastic loss and storage modulus decrease. From the viscoelasticity study, except for 90:10 OWR, it is observed that as the oil water ratio increase, the yield stress and the flow point also increases. The 90:10 OBM shows no viscoelasticity behavior.
Comparing the extreme 60:40 and 90:10 OBMs (i.e. as OWR increase), the experimental result shows that the sagging index increases by 9%. The dynamic sagging factor decreases as the ratio of storage modulus to loss modulus increases (i.e. as OWR decrease).
Except for high viscosity and hydraulics, the overall analysis of drilling fluids shows that the 60:40 OWR is the better in terms of sagging, filtrate loss and hole cleaning performance.
Comparison Between Two Forecast Systems Implemented With WAM and WaveWatch 3 for the North Atlantic
Authors: Bento A. Rute , Gonçalves Marta , Campos Ricardo , Guedes Soares C. 
Published: October 2016

The performance of two operational forecasting systems implemented for the North Atlantic area is compared. One forecast system runs the WAM model and the other using the WaveWatchIII model, both driven by GFS wind fields and with the same resolutions for time and space.
The GFS wind fields used to drive the models have a spatial resolution of 0.5° by 0.5° and a time resolution of 3h. Regarding the geographical grids implemented, they cover the North Atlantic from the longitude of 90° West to 33° East and from the latitude of 80° North to 2° South, with a fine grid resolution of 0.5 by 0.5 degrees. The wave spectrum is discretized using 30 frequencies, being the lowest frequency equal to 0.0418 Hz, and 36 directions. A 4-days warm up was implemented and a 4-days forecast was calculated.
In general both models performed well, as forecasting systems, presenting the same behavior and magnitude of values, when compared to the in-situ measurements.
Novel Experimental Investigation on Vortex Induced Motions of a Tension Leg Platform
Authors: Ramirez Miguel A. M. , Fernandes Antonio Carlos 
Published: October 2016

Recently, a growing interest has been seen in vortex induced motions of offshore units. These induced motions are significantly relevant for the design of mooring systems and risers of offshore platforms.
This work analyzes the vortex induced motions (VIM) of a Tension Leg Platform (TLP) when submitted to currents. The model tests were carried out in the fKN@LOC/COPPE-UFRJ laboratory facilities. Furthermore, a novel arrangement to represent the TLP tendons in shallow current channels is presented and discussed. This experimental set-up is innovative since, to avoid the set down, a tower has been implemented. TLP vertical motions are restrained and necessary stiffness for horizontal modes is provided by springs.
The ultra-reduced model with four square columns and four pontoons in closed configuration was built using a scale of 1:200. The range of current velocities was from 0.33 to 2.59 m/s. and five angles of attack were considered: 0, 11.25, 22.50, 33.75, 45 degrees. The reduced velocity reached a very high value of 32 for 45 degrees of heading.
Results have shown that the induced motions are dependent on the angle of attack and the current speed. For zero degrees of heading a typical bell curve of VIM was observed. On the other hand, for 45 degrees, motions increase steadily with current speed.
Impact of Pore Topology on Gas Diffusion and Productivity in Barnett and Haynesville Shale Plays
Authors: Davudov Davud , Moghanloo Rouzbeh Ghanbarnezhad , Dadmohammadi Younas , Curtis Mark , Javadpour Farzam 
Published: October 2016

This study evaluates gas transport through matrix pores in Barnett and Haynesville shale gas plays. Gas is mainly stored in a compressed phase in small pores or as a desorbed phase on the surface of the pores. At the early stage of production, gas decompression/expansion within networks of large fractures connected directly to the wellbore is the dominant production mechanism; however, after some time (a couple of weeks up to few months) diffusive flux from the body of kerogen is triggered in response to the pressure drop realized at the fracture face. In this study we present a comprehensive study of the importance of various diffusion patterns to predict the productivity of shale reservoirs at the later stage of production.
We present transient diffusion models to address gas diffusion from kerogen bodies through connected pores with different shapes (slit or cylindrical) toward fractures. In this model we use a new set of boundary conditions as opposed to traditional Dirichlet and Neumann types of boundary conditions. The analytical solution is validated using a set of experimental data.
In the next step, we choose wells from gas producing parts of Barnett and Haynesville shale plays. Based on detailed studies of scanning electron microscope (SEM) images, we identified two different governing patterns for diffusive flux in the shale matrix: inter diffusion in Barnett and intra diffusion in Haynesville. We used production data to differentiate the matrix contribution using conventional methods of rate transient analysis. Using the analytical model, we compared the matrix contribution parts of production data between Barnett and Haynesville shale plays. We found an excellent match between observed small-scale pore shapes and field production data in our transient diffusion model. Based on results, the inter diffusion pattern provides greater flux; while everything else remains equal, Barnett wells benefit more from matrix contribution than those of Haynesville. Results indicate that the distribution of connected pores in the shale matrix has significant effect on the matrix contribution.
The main contribution of this work is providing a transient flow model for gas transport through shale matrix accounting for the impacts of dominant shape of the connected pores and their abundance in the matrix texture (namely: organic or inorganic part). Our results suggest that the inter diffusion in Barnett shale play outperforms the intra diffusion mechanism in the Haynesville field. In addition, the more cylindrical pores, the better the performance. In general, the topology of the connected pores as well as their abundance within kerogen or inorganic matters can greatly influence long-term productivity of gas wells.
Analysis of Variance to Determine the Effect of Hull Form Parameters on Resistance and Seakeeping Performance for PSV Hulls
Authors: Boyd Nicholas , Molyneux David 
Published: October 2016

Throughout the world many Platform Supply Vessel designs have been proposed as the optimal form for their given operating environment, but evaluating these claims has been difficult due to a poor understanding of the relationships between hull form shapes and performance for these vessels. This paper presents the results of analysis aimed at determining these relationships.
Results of CFD calculations to determine the Effective Horsepower/tonne for a series of PSV designs were presented in the paper A step towards an optimum PSV Hull form. This paper presents results for 16 separate hull forms, which were designed as each possible combination of four two-level hull form parameters. The hull form features considered were bow shape (vertical stem or bulbous), flat of bottom (flat or deadrise), length of parallel mid body (short or long), and stern shape (convention or integrated); resistance was calculated at two typical operating speeds (10 and 14 knots). This set of results was favourable for analysis using the statistical design of experiments technique: analysis of variance, which was used to determine the relationship between the hull and resistance performance.
The same hull form series was used to study the effects of the hull form parameters on motions in head waves. A 2 level factorial experiment was designed based on the hull parameters with the heave and pitch response calculated using the potential flow ship motion prediction code Shipmo3D, for each of two representative wave conditions (summer light seas and winter heavy seas) at the zero speed and 10 knot operating speed. Analysis of variance was used to analyze the heave and pitch responses measured, and was used to determine the relationship between each hull parameter and each response.
In both cases a 5% F-test was used to determine the significance of each parameter studied, and the significant effects were analyzed to determine their contributions to the overall model of the data.
The results have found the relationships between the hull design parameters and the Effective Horespower/tonne, heave, and pitch response of the vessel, indicating which factors provide the largest contribution to minimizing each response. The interaction effects between factors were also examined to allow for a generalized understanding of the resulting effect of selecting one hull parameter over another. A numerical model combining all significant factors was fitted to the data, allowing for multiple objective optimization to determine which hull forms provide the most desirable performance for each response.
Scheduling of Offshore Support Vessels on the Grand Banks
Authors: Molyneux David , Boyd Nicholas 
Published: October 2016

The Grand Banks off the coast of Newfoundland and Labrador present a challenging environment for the offshore oil industry. There are currently three oil producing developments, with an average distance offshore of approximately 185 nautical miles. The environment is characterized in winter by strong winds, high waves and the presence of pack ice. In the summer the area is prone to heavy fog and low visibility. Offshore support vessels are a key element of any marine based drilling and production system and they must function effectively in this environment. Their key role is to provide a timely delivery of supplies (and if necessary personnel) to and from the offshore platform.
The main challenge for the existing vessels operating on the Grand Banks is that there is a high level of seasonal variation in the weather conditions between winter and summer. The research results presented in this paper were a preliminary attempt to understand the relationships between the distance offshore of the production or drilling platform, the number of supply vessels serving a platform, vessel speed, weather conditions and the required slack in the vessel schedule to provide a reliable service. This analysis was undertaken as there is significant potential for offshore development within the Flemish Pass Basin, which is even further offshore (270 nautical miles) and in a more severe winter wave regime.
The results show that although the current Offshore Support Vessel fleet is satisfactory for 185 nautical miles offshore, there will need to be some changes in order to provide effective service when developments move further offshore. This may include a combination of more ships to service an offshore platform, faster ship speeds, reduced frequency of delivery, or increasing the limiting wave height for lifting operations.
First- and Second-Order Wave-Induced Dynamic Response of Submerged Floating Tunnels
Authors: Leira Bernt J. 
Published: October 2016

Submerged floating tunnel concepts have been developed for the purpose of crossing wide straits with a span length of many kilometers. The frequencies of the first dynamic modes of these structures may typically be of the order of one minute or more. This implies that amplified dynamic response effects need to be assessed both for the wave-frequency and the low-frequency regimes. The first order (i.e. wave frequency) dynamic response has been found to depend strongly on wave direction and wave spreading. This is also be expected to apply for the second-order response. Furthermore, the small inherent damping levels for the low-frequency response will imply that high dynamic amplification may occur.
These issues are addressed by the present paper. Computational methods for evaluation of the hydrodynamic loading and the associated dynamic response are addressed. Both simplified assessment as well as more refined calculation procedures are considered.
A specific case study is considered for the purpose of illustrating the relative effects of the various response components. The example structure is a tunnel with a double cross-section which was developed for crossing of the Sognefjord located at the West Coast of Norway. The same type of floating tunnel is also relevant for crossing of other fjord spans.