bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Hydrodynamic Loads and Flow Patterns Near an Escort Tug in Oblique Flows
Authors: Jahra Fatima , Islam Mohammed , Thanyamanta Worakanok , Molyneux David 
Published: October 2015

The present research investigates the hydrodynamic forces and moments and the flow pattern near the hull of an escort tug at steady oblique flow conditions. An escort tug is modelled and numerical simulations have been carried out using a commercial RANS solver. In the simulations, the viscous flow field is calculated by the finite volume method, adapting the k-ε turbulence model. Free surface is modeled using the Volume of Fluid (VOF) approach for calm water condition. The hull is assumed fixed in space with an even keel. Grid dependency studies are conducted to obtain insight into the reliability and accuracy of the results. Flow velocities around the escort tug as well as integral variables are computed at different Froude numbers and compared to the corresponding measurement data available in the public domain. The measurements was completed using a Planar Motion Mechanism (PMM) apparatus to measure the resistance, side force and yaw moment of the tug hull. Additionally, the velocity distributions on the upstream and downstream sides of the tug were measured by Particle Image Velocimetry (PIV).
The measurements and simulations have been completed at one draft, and at 15°, 30° and 45° inflow conditions. A reasonable agreement has been obtained between the predicted axial and lateral forces and the corresponding measurements. The flow pattern and the velocity distribution at different drift angle are comparable with the measurements. The variation of the pattern of flow separation at the suction side of the hull at different yaw angle is also analyzed and presented.
Fatigue Evaluation Procedures for Multi-Axial Stress State in Welded Joints
Authors: Hong Jeong K. , Forte Thomas P. 
Published: October 2015

The Battelle structural stress method (BSSM) for fatigue life evaluation is examined for multi-axial stress states that develop due to uniaxial loading in welded structures. The resultant multi-axial stress state due to simple uniaxial loading is easily observed in common joint types such as a plate with a welded tube or a plate with an angled attachment. In these joint types, under simple loading, the stress distribution at the location of failure along the weld line shows significant in-plane shear stress (parallel to the weld line) as well as normal stress (normal to weld line). Although the fatigue data, as exemplified by the inverse slope of the S-N curve for the subject joints under uniaxial loading, are observed to be similar to that for normal-loading-mode dominant (Mode I) failures in welded joints, when only the normal structural stress is considered for these joints the predictions of both the fatigue failure location and the fatigue life using the master S-N curve approach are inaccurate because the in-plane shear stress plays a significant role in the development of the crack.
The slope of fatigue data exhibited in S-N curves taken from weld fatigue data for resultant multi-axial stress state generated by uniaxial loading is different from multi-axial fatigue loading conditions for tubular joints as discussed in the recent work [OMAE2014-23459].
In this article, the fatigue behavior of welded joints with multi-axial stress states is evaluated using an effective equivalent structural stress range parameter that is formulated as a von Mises form of the combined normal and in-plane shear equivalent structural stress ranges. When the effective equivalent structural stress range parameter is employed, the fatigue failure location can be predicted correctly. It is also found that the cycles-to-failure data from the subject joint types are comparable with the master S-N curve for Mode I loading dominant behavior (inverse slope of 3.125). Therefore, the master S-N curve that was developed for Mode I failures can be equally applicable for fatigue life prediction for these joints by replacing the equivalent structural stress range with effective equivalent structural stress range on the ordinate axis.
Validation of Global Performance Numerical Design Tools Used for Design of Floating Offshore Wind Turbines
Authors: Allen Christopher K. , Goupee Andrew J. , Dagher Habib J. , Viselli Anthony M. 
Published: October 2015

In an effort to harness the abundant offshore wind resource over deepwater, the development of numerical design tools for floating offshore wind turbines (FOWTs) has progressed steadily in recent years. However, at present, a validated model capable of completely coupling the full elastodynamic response between the mooring system, floating support structure, turbine tower and the wind turbine is not commercially available.
The University of Maine has developed a new FOWT design, VolturnUS, which utilizes a concrete semi-submersible hull. For the VolturnUS design effort a number of numerical models were developed to analyze the system’s global performance. This paper presents the results of a validation study conducted to quantify the accuracy and suitability of a subset of these models for use in the design of the VolturnUS FOWT. Validation was conducted via comparisons of numerical model results to test data obtained from a 1:50 scale model testing campaign conducted by the University of Maine at the Maritime Research Institute, Netherlands offshore basin.
The validation study evaluated the performance and capabilities of the numerical models over a range of design conditions. Emphasis was placed on design load cases (DLCs), which were found to govern the design of the FOWT. The DLCs follow the American Bureau of Shipping’s (ABS) Guide for Building and Classing Floating Offshore Wind Turbines.
Through this method of model validation this work sought to quantify the numerical models’ accuracy, highlight their limitations, justify design assumptions, and identify areas requiring further development in the field of FOWT numerical modeling.
Numerical Simulation of Wake Effect in Nets Under Steady Current
Authors: Cifuentes Cristian , Kim M. H. 
Published: October 2015

To accurately describe the dynamic response of aquaculture cages exposed to current loading, it is necessary to consider the reduction of fluid velocity due to the presence of the net. In this study, three wake models, originally developed for riser interaction, are applied to a cylindrical net to evaluate drag force, volume and projected area reduction when exposed to steady currents. The results are compared to available experimental data to validate the methodology and evaluate the wake models’ accuracy. The net has been modeled using the commercial software OrcaFlex. This tool is a fully nonlinear finite element software, capable to compute forces and displacements of the net when exposed to current and wave loading.
Calculations were performed under a series of current speed and three ballast weight conditions. The effect of the number of elements used to describe the net is analyzed as well. Results without including wake effect show good agreement for drag force up to moderate current speeds.
Nevertheless a significant improvement on drag force results was achieved when wake effect is included. Yet, at high current speed and heavier ballast, drag force is over predicted. Minor differences were found when different wake models are used. In addition, it is concluded that an increase on the number of elements shows no significant influence on drag force results. On the other hand, calculations for volume and projected area reduction get closer to experimental values. The findings confirm the relevance of wake effect on nets and serve as validation of the present numerical procedure.
Effect of Lay Angle of Anti-Buckling Tape on Lateral Buckling Behavior of Tensile Armors
Authors: Zhou Chongyao , Sævik Svein , Ye Naiquan , Ji Guomin 
Published: October 2015

During deep water flexible pipe installation, the pipe is normally free hanging in empty condition from the installation vessel to the seabed. This will introduce large hydrostatic forces to the pipe causing true wall compression. In addition, the pipe will be exposed to cyclic bending caused by waves and vessel motion. The combination of true wall axial compression and cyclic bending may lead to tensile armor instability in both lateral and radial directions. If the anti-buckling tape is assumed to be strong enough, the inner tensile armor will lose its lateral stability first due to the gap that may occur between the inner tensile armor and the pipe core, hence restricting the available friction restraint forces. These may further be reduced by cyclic motions that act to create slip between the layers, hence introducing lateral buckling of the tensile armor, with associated severe global torsion deformation of the pipe, ultimately causing the pipe to lose its integrity.
The anti-buckling tape is designed to prevent the radial buckling behavior, however, its effect on lateral buckling has not yet been documented in available literature. In the present paper, the effect of the winding direction of the anti-buckling tape on the twist of the cross section is studied, including comparisons with available test data from literature.
Numerical Study on Fish Tail Shaped Rudder for Improved Ship Maneuvering
Authors: Babu Mannam Naga Praveen , Krishnankutty P. 
Published: October 2015

Maneuvering is an important safety aspect in ship operations so as to avoid accident of ships in seaways and more critically in the restricted area of waterways. IMO stipulates many safety regulations on ship maneuverability in open sea conditions and the local authorities may have additional regulations in harbor, canal and other restricted waterways. The effectiveness of rudder has substantial influence on the maneuverability of a ship. It is often difficult to increase the size of the rudder, to get higher control force/moment, due to the geometrical restrictions of the aft aperture of the ship. A hydrodynamically efficient rudder section addresses this problem to some extent. Most of the fishes maneuver efficiently using their tail. The fish tail functions almost similar to that of a rudder for its movements and navigation. In general, ship with flap rudders and fish tail shaped rudders perform maneuverability better compare to a ship fitted with a conventional rudder having the same underwater surface area. In fishtail shaped rudders, the shape and movements promote good flow patterns in a wider range of rudder angles. In a fish tail, the trailing edge accelerates the flow and recovers lift over the aft section of the rudder. This results in the generation of a higher lift and thus helps in reducing the turning diameter of the vessel.
The studies carried out with two rudder types — conventional rudder and fish tail shaped rudder — are presented in this paper. Numerical simulations are performed on these two rudders, both having the same surface area, for different rudder angles in free stream condition. The lift force generated by the fish tail shaped rudder is found to be higher than the conventional rudder. The flow across and the hydrodynamic forces acting on the sections are determined using a commercial CFD code. The effectiveness of the fishtail rudder is also brought out from the numerically simulated turning maneuver of a chosen ship fitted with the same rudder.
Estimation of Most Probable Maximum From Short-Duration or Undersampled Time-Series Data
Authors: Agarwal Puneet , Walker William , Bhalla Kenneth 
Published: October 2015

The most probable maximum (MPM) is the extreme value statistic commonly used in the offshore industry. The extreme value of vessel motions, structural response, and environment are often expressed using the MPM. For a Gaussian process, the MPM is a function of the root-mean square and the zero-crossing rate of the process. Accurate estimates of the MPM may be obtained in frequency domain from spectral moments of the known power spectral density. If the MPM is to be estimated from the time-series of a random process, either from measurements or from simulations, the time series data should be of long enough duration, sampled at an adequate rate, and have an ensemble of multiple realizations. This is not the case when measured data is recorded for an insufficient duration, or one wants to make decisions (requiring an estimate of the MPM) in real-time based on observing the data only for a short duration. Sometimes, the instrumentation system may not be properly designed to measure the dynamic vessel motions with a fine sampling rate, or it may be a legacy instrumentation system. The question then becomes whether the short-duration and/or the undersampled data is useful at all, or if some useful information (i.e., an estimate of MPM) can be extracted, and if yes, what is the accuracy and uncertainty of such estimates.
In this paper, a procedure for estimation of the MPM from the short-time maxima, i.e., the maximum value from a time series of short duration (say, 10 or 30 minutes), is presented. For this purpose pitch data is simulated from the vessel RAOs (response amplitude operators). Factors to convert the short-time maxima to the MPM are computed for various non-exceedance levels. It is shown that the factors estimated from simulation can also be obtained from the theory of extremes of a Gaussian process. Afterwards, estimation of the MPM from the short-time maxima is explored for an undersampled process; however, undersampled data must not be used and only the adequately sampled data should be utilized. It is found that the undersampled data can be somewhat useful and factors to convert the short-time maxima to the MPM can be derived for an associated non-exceedance level. However, compared to the adequately sampled data, the factors for the undersampled data are less useful since they depend on more variables and have more uncertainty. While the vessel pitch data was the focus of this paper, the results and conclusions are valid for any adequately sampled narrow-banded Gaussian process.
Residual Stress Evaluation and Buckling Analysis of Carcass Layers in Flexible Pipes Using 3D Finite Element Model
Authors: Tang Minggang , Yan Jun , Chen Jinlong , Yang Zhixun , Yue Qianjin 
Published: October 2015

A carcass layer plays an important role in unbonded flexible pipes to resist the high level of external pressure without buckling collapse. The layer is made of an interlocked helically wound metal wire of profiled section that cold-deformed by a series of rollers. In typical design and analysis process of the carcass layer, the initial stress is always assumed to be zero. During the carcass layer manufacturing (a cold forming process), the metal strap is however subjected to varies of squeezing and bending and deformations to take “S” shape, and then the profiled wire to a cycling sequence of bending, squeezing and twisting deformations, which take it beyond its material elastic limit. The residual stress is therefore introduced and could has effect on the critical pressure of the carcass layer.
This paper presents a 3D finite element model to investigate the detailed residual stress distribution and variation during the forming process of the carcass layer. A study case using a 3D ring model is presented to systemically study the influence of imperfections, especially the residual stress, on the critical pressure of carcass layers.
Development of a Ship Performance Simulator in Actual Seas
Authors: Tsujimoto Masaru , Sogihara Naoto , Kuroda Mariko , Sakurada Akiko 
Published: October 2015

Greenhouse gas shall be reduced from shipping sector. For that purpose the regulation of EEDI (energy efficiency design index for new ships) and SEEMP (ship energy efficiency management plan) were entry into force from 2013. In order to improve energy efficiency of ships in service it is necessary to predict the fuel consumption in actual seas.
In order to reduce GHG emission from ships, a Vessel Performance Simulator in Actual Seas has been developed. It simulates ship speed and fuel consumption at steady condition by using weather data and designated engine revolution. Physical models for hull, propeller, rudder and engine are used in the simulator. Especially steady wave forces, wind forces, drift forces, steering forces and engine/governor model are important factor for the estimation.
The fuel consumption should be evaluated combined the ship hydrodynamic performance with the engine/governor characteristics. Considering the external forces by winds and waves, the operation point of the main engine is important for the estimation, since the torque limit and the other limit of the engine/governor are affected to the ship hydrodynamic performance. To prevent the increase of fuel consumption in service, the engine control system by the Fuel Index has been applied to present ships. In rough weather condition the revolution of the main engine is reduced to lower revolution by the Fuel Index limit. It causes the large decrease of ship speed but reduces the fuel consumption due to reduction of engine revolution.
Using the simulator the navigation performance of a container ship, a RoRo vehicle carrier and a bulk carrier is simulated along the route.
In this paper following contents are discussed; 1) evaluation of the physical model; steady wave forces, wind forces, drift forces, steering forces and engine/governor model, 2) simulation and validation of the physical model by tank tests and on-board measurements and 3) effectiveness of the ship performance simulator for GHG reduction.
A Fundamental Research on the Effects of a Floating Berth on Reduction of Tsunami Damages in a Harbor: Reduction Effects of the Breaking of Mooring Lines and Running on a Quay
Authors: Murata Kazuki , Ohno Masato , Ikoma Tomoki , Masuda Mitsuhiro 
Published: October 2015

Tsunami consecutively brings about several types of disasters, which is described as “disaster chain.” In the case that vessels are moored to the quay, the breaking of the mooring line possibly causes drift or collision with other vessels. There is also a case that a mooring tether of the vessel moored to the floating pier is not broken in the damage of tsunami, which was confirmed at Shiogama port in Miyagi when the East Japan Great Earthquake occurred on March 11, 2011.
The objectives of this paper are to clarify the reduction effect of mooring line force when a vessel is moored to a floating berth. The three-dimensional MPS method is used with advantages of floating berth considered. We simulated a vessel with the cargo carrier of 3,000t. Especially, by changing the wave elevation and the incident angle, the responses of the mooring tension which acts on the vessel moored to a floating berth and to the quay respectively are compared, and its reducing efficiency is examined. A conclusion is reached that, when tsunami incident wave angle is 90 degrees, mooring vessels to a floating berth can be expected as a solution to reduce the problems of vessel’s running onto a quay, in comparison with mooring them at a quay wall. Also, we propose suitable anchoring methods according to the size of the vessels.
Localizing Swimming Objects in Noisy Environments by Applying Nearfield Acoustic Holography and Minimum Energy Method
Authors: Ziemer Tim 
Published: October 2015

A problem in localizing individual swimming objects acoustically is the high amount of strongly fluctuating ambient noise due to turbulent pressure fluctuations, thermal and seismic noise, motoring vessels, wind and marine mammals. In littoral and other shallow waters additionally the complex boundaries produce absorption of high-frequency components and strong reverberation in other frequency regions, refraction due to sudden changes in temperature and scattering from the rough sea surface and floor.
In this paper localization of a single swimming object in presence of disturbing sources and noise is simulated. Low-frequency nearfield acoustic holography (NAH) based on vector hydrophone array measurements is combined with minimum energy method (MEM) to increase detection certainty.
This combination of NAH and MEM appears to be a reliable and robust detection method suitable e.g. for sort-range navigation in littoral waters and for iceberg detection in open waters.
The Research and Application of the Ice-Resistant Technology for the Offshore Structures in Bohai Sea
Authors: Du Xiaying , Cui Yujun , Liu Yuan 
Published: October 2015

The sea ice of China’s Bohai Sea has strongly affected the safety of the offshore structures in every winter. The ice load has become the principle load to be controlled during the design of offshore structures. In order to minimize the damages caused by sea ice, the researchers in Bohai oil field have conducted thorough studies on the ice-resistant technology, which have been tested and improved through the application in the ice-resistant test. This paper presents summarization and review on the studies and applications of the ice-resistant technology in Bohai Sea.
Based on the observation data in the past several decades, this paper recommends design environment parameters for sea ice in Bohai Sea, including ice period, ice thickness, ice speed and ice flow direction. Fundamental research on the ice loads and ice-induced vibration are introduced in this paper. The methods and results of the experimental studies and field tests for the research are illustrated systematically. Moreover, this paper reviews the application of the ice-resistant technologies and structures in Bohai oil field and discussed their respective deficiency. Meanwhile, an ice-resistant emergency case is presented to illustrate the compositions and operation mode of the emergency management system of Bohai oil field.
Hydrogen Induced Corrosion Cracking and Crevice Corrosion Behavior in Natural Sea Water of Super Duplex Seam Welded Tubes for Umbilicals Applications
Authors: Evin Harold N. , Peultier Jerome , Thevenet Gilles , Wagner Olivier , Romazzotti Henri , Roques Jean-Philippe 
Published: October 2015

Umbilicals are important tubes assembly essentially used for subsea equipment controlling functions and fluid injection. Super duplex stainless steel 2507 (UNS 32750 / EN 1.4410) has been the historical grade used for its corrosion resistance and mechanical properties. The Oil and Gas industry is gradually working on the exploration and exploitation of offshore and deep offshore resources. These operating conditions lead to new philosophy in the design of subsea umbilicals, which are evolving to answer the needs of new functionalities. Recent years development supported by O&G operators, have seen innovative super duplex stainless seam welded tube solution being used for their high mechanical characteristics (YS0.2≥ 750 MPa; UTS≥ 900 MPa), tight dimension tolerances, and their ability to generate cost saving during installation. The specific metallurgical manufacturing route for the 2507 strip together with an efficient roll forming process and NDT control allows to obtained tubes for umbilicals which push the usual boundaries of utilization of this super duplex grades.
In this paper, Hydrogen Induced Stress Cracking (HISC) behavior, possible failure mode of the super duplex stainless steel tubes exposed to cathodic protection in the termination unit, was extensively studied. A stress load of 110% YS0.2 was applied using a dead weight bench and the tubes performance was characterized after 500h of exposure in synthetic sea water under cathodic protection. Crevice corrosion is also a reported failure mode for umbilical tubes. Corrosion resistance of the 2507 seam welded tubes was also assessed in natural sea water in crevice conditions at open circuit potential (OCP). No failure was observed during the HISC testing in synthetic sea water after 500hours of exposure and no micro-crack was detected on the tubes after characterization. The metallurgical microstructure of the laser weld is not preferential initiation zone for crevice corrosion.