bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of a Nonlinear Riser-Soil Interaction Model for Abaqus
Authors: Akula Venkata M. K. , Datye Deepak
Published: October 2015

For a steel catenary riser system, the touch-down point is often a concern as it can influence the structural response of the riser and its performance. Although, riser configurations can be designed to withstand wave loading, internal pressure, external pressure, and thermal loads; the design of risers taking into account the interaction between the riser and the soil, with cycles of contact and separation, still remains challenging. More specifically, when the riser contacts the seabed surface, it penetrates into the soil material. This penetration can cause suction-type behavior when the riser moves away from the surface. Further, it causes permanent deformation in the soil so the riser has to traverse additional distance prior to re-contacting the seabed surface. For formulating a robust riser design using the finite element method, accurate modeling of this nonlinear riser-soil interaction is needed.

In the majority of situations, risers are modeled with beam elements. This is an efficient approach considering that a riser-pipeline system can be several thousand meters in length and using shell or brick elements for modeling such a system becomes computationally expensive. In addition, the seabed surface is often modeled as a rigid surface. The riser-soil interaction behavior is then incorporated into the finite element analysis either by defining springs at the contacting nodes or by modifying the normal contact stiffness for the interaction. However, these methods do not entirely capture the nonlinear riser-soil interaction behavior.

In this paper, we discuss the modeling of the nonlinear riser-soil interaction through the use of a user subroutine that runs in conjunction with a finite element analysis using Abaqus. This subroutine is intended to provide a special contact interaction property definition between the riser and the seabed. This contact property definition focuses primarily on the normal behavior although frictional resistance is also considered. The results of the simulation and the insights gained are included.
The Study on Hull Structure Strength Analysis and Opening Calculation of CJ46 Jack-Up Drilling Unit
Authors: Ji Zeng , Gang Chen , Jian Mo , Yuhan Wang , Wei Zhang
Published: October 2015

The structural strength of jack-up units is the key issues in the design of ship and ocean engineering structures. Based on ABS MODU, the yield strength of CJ46 self-elevating drilling platform main hull structure is checked. Firstly, the environmental loads (wind, wave and flow) in three loading conditions which are required by specification are calculated by using GeniE (DNV). Then the 3D finite element model of main hull structure is established. The yield strength is checked and the results shown the large stress areas are leg well, jackcase which is connected with the leg and bulkhead which is main support structure under the cantilever sliding device, while the results meet the requirements of ABS MODU. Finally, the influence of the openings located in main longitudinal bulkheads are evaluated, meanwhile the main longitudinal bulkheads under skidding box need particular concern.
The Study on the Method of Film Thickness Control by Coating Spray Robot for Ocean Engineering
Authors: Liansheng Yang , Yi Zhou , Xuemei Liu , Aiping Li , Ji Zeng
Published: October 2015

Combined with the anticorrosion character and requirement of the ocean engineering, the painting growth model sprayed by the coating spray robot is studied in this article. A special experiment platform is set up to carry out the test orthogonal experiment design method (OED), and enough data are recorded. Experimental data are used to build back propagation (BP) neural network as a sample set, while validated by the genetic algorithm (GA). Then the dry film thickness (DFT) growth model is established to analyze the relevance between dry film thickness and influence factors such as distance between the spray gun and surface, spray gun nozzle, velocity of the spray gun and so on. The model can provide important theoretical direction for the use of spray robot in the ocean engineering.
Experimental Studies of Pressure Loss in Inclined Pipe in Slurry Transport for Subsea Mining
Authors: Masanobu Sotaro , Takano Satoru , Fujiwara Tomo , Kanada Shigeo , Ono Masao
Published: October 2015

For subsea mining, the estimation of pressure loss in the pipe of lifting system and the flexible pipe to connect the mining tool and the lifting system is important to design the mining system. The configuration of flexible pipe is expected to have an inclined part.

In the present paper, the authors carried out the experiment to measure the pressure loss in inclined pipes using alumina beads to investigate the effect of inclination angle of pipe on the pressure loss. Furthermore, a mathematical model to estimate the pressure loss in inclined pipes was proposed and validated through the experiments. As the result of the validation, it was confirmed that the proposed model could be applied to the pressure loss estimation in inclined pipes.
Electric Impulse Technology: Long Run Drilling in Hard Rocks
Authors: Anders Erik , Lehmann Franziska , Voigt Matthias
Published: October 2015

The costs of drilling in hard rock depend significantly on the available drilling technology. Conventional drill bits are especially adapted to the needs of the oil and gas industry but they are limited for drilling in crystalline formations. The Electric Impulse Technology offers a promising alternative for this purpose. The splitting effect of electrical explosions inside the rock is used to destroy the rock instead of working mechanical against the compressive strength of the rock. In a project funded by the BMWi (project number 0325253) a drill head was developed, which consists of a pulse power source of up to 500 kV and electrodes for a 12 ¼″ borehole. The drill head is designed for downhole pressures up to 1000 bar and temperatures up to 200 °C. A test stand has been implemented at the TU Dresden. Drilling tests under borehole like conditions could be performed. Drilling speeds of 1 m/h could be proven. The follow-up project started in the end of 2014. The drill head will be optimized and the power supply will be designed. The total system will be used in a test well and investigated.
A Revised Methodology for the Calculation of MODU Watch Circles
Authors: Quigley Conor , Williams Dara
Published: October 2015

As the industry continues to push the boundaries of offshore exploration into deeper water depths and harsher environments there is an increased need to ensure the integrity of both the drilling riser and wellhead in the event of loss of station-keeping in dynamically positioned (DP) rigs. In order to determine vessel limiting operating/alert offsets it is necessary to carry out a vessel drift-off analysis which predicts the vessel drift-off speed and direction in the event of a DP failure.

This analysis is typically performed for a limited combination of environmental conditions (usually collinear wind, wave and current) and will generally assume a vessel position that is directly above the wellhead. Whilst the results of the standard drift-off analysis, and associated drift-off plots, are useful in determining expected drift-off speed and feasibility of the emergency disconnect sequence (EDS), the outputs are of little operational use to the rig personnel in determining allowable operational/alert offsets for day to day operations. As the vessel is rarely located directly above the wellhead and environmental conditions can vary significantly in both direction and magnitude over the drilling campaign a more comprehensive analysis methodology and set of load cases is required in order to develop useful inputs to the well specific operating guidelines (WSOG).

The current standard industry approach is to generate drilling riser operability envelopes independently of drift-off curves and thus recommended operating offsets do not account for drift-off speed, reaction times or EDS times. This can lead to a potential lack of conservatism in WSOG. In order to avoid this lack of conservatism in calculation of operating offsets a coupled steady-state/transient response analysis approach is required to ensure that a DP failure event at limiting operational offset does not lead to damage to the wellhead or riser system.

A new revised methodology for the calculation of allowable operating windows and associated alert offsets is presented in this paper. This new methodology couples both the steady state operating limits of the vessel and the transient system response during a drift-off, due to DP failure, in order to present a comprehensive go/no-go operability chart of allowable offset vs. environment for use as input to the WSOG.
Numerical and Experimental Study on Energy-Harvesting Piezoelectric Flags
Authors: Xia Yifan , Michelin Sébastien , Doaré Olivier
Published: October 2015

Placed in a fluid flow, a cantilevered flexible plate flaps spontaneously above a critical flow velocity. The resulting self-sustained vibrations of such a flag may be used to produce electrical energy and power an output circuit using piezoelectric patches covering the flag that deforms with the flapping motion. Previous work showed only moderate harvesting efficiency with a resistive output circuit, but proposed numerous directions for improvement. We propose a numerical and experimental investigation of the coupled dynamics of such a fluid-solid-electric system, and analyze the influence of the output circuit on the dynamics and harvesting efficiency. In particular, inductive-resistive circuits are considered. Our numerical results show that such resonant circuits lead to a destabilization of the system and a spontaneous flapping at lower fluid velocities. Also they significantly increase the energy harvesting efficiency of the piezoelectric flags as a result of a frequency lock-in between the flag and the electrical circuit. Wind tunnel tests are performed with prototypes of piezoelectric flags and basic resonant circuits. We show that such circuits effectively enhance the energy harvesting performance when they are in resonance with the piezoelectric flag. Meanwhile, the internal resistance of the inductive elements also shows an important influence on the harvested electrical power. In both numerical and experimental studies, the importance of piezoelectric coupling strength is observed. Our results show that promising efficiency enhancements of such flow energy harvesters would be achieved through the optimization of the output circuit as well as development of new piezoelectric materials.
Dynamic Modeling of Towed Cable System Using the Nodal Position Finite Element and Symplectic Integration
Authors: Li G. Q. , Lian Lian , Zhu Zheng H.
Published: October 2015

The cable of towed underwater system have a character of low tension, in order to overcome this singular problem during numerical calculation, the bending stiffness is included in the bar model, or using the beam model. however, we choose an alternative method called nodal position finite element method, it is different from the traditional finite element method, this alternative method is formulated in term of element nodal position that different with the nodal displacement used in traditional finite element. The model equation is derived from the principle of virtual work, consideration of the hydrodynamic drag force, gravity force, buoyancy and internal damping model. The energy conservative time integrator is preferred for the long term simulation, so we build up a simulation program that using the nodal position finite element method and symplectic leapfrog time integrator for the dynamic analysis of the towed body system. Firstly, the robustness of the proposed time integrator is verified by the elastic spring pendulum, and compared with the traditional frequently used time integrators such as fourth-order Runge-Kutta method and Newmark method, the results show that the proposed approach is accurate and preserves the system energy over long term simulation, then the proposed time integrator is applied to the dynamic modeling of the elastic cable towed system, the well agreement with Sea trail experiment date demonstrates that the simulation program is robust and accurate.
The Research on the Fatigue Analysis of the Jack-Up’s Leg Based on SESAM Software
Authors: Ji Zeng , Hongtao Yuan , Chao Wang , Yuhan Wang , Jian Mo
Published: October 2015

In this paper, a fatigue assessment based on spectrum analysis for Jack-up’s legs is performed by adopting stochastic method for three water depths using DNV/SESAM. Firstly, force transfer function is determined by the DNV/WAJAC for each wave direction considered. Secondly, members end stresses are computed by the DNV/SESTRA. Then SCF (stress concentration factors), DAF (dynamic amplification factor) and P-delat effects are applied in the stress range calculations. Finally, the cumulative fatigue damage of unidirectional waves to the critical connections is determined by the DNV/FRAMEWORK. The critical connections at the chords and the braces are selected and reviewed for fatigue life calculation. The results show that the legs have fatigue lives exceeding the expected design life of Jack-Up Drilling Unit of twenty-five (25) years and meet ABS requirement.
Ethylene Glycol as Gas Hydrate Stabilising Substance
Authors: Schulz Anne , Strauß Heike
Published: October 2015

Gas hydrates are solid substances consisting of water and gas which are stable under high pressure and low temperature conditions. After Davy discovered chlorine hydrate in 1810, gas hydrates from natural gas were found to be the reason for gas pipeline plugging in 1934 by Hammerschmidt. In 1965, the Russian scientist Makogon discovered natural gas hydrate deposits. This was the beginning of research in the geological occurrence of the gas hydrates.

Today, hundreds of gas hydrate wells for exploration have been drilled all over the world in the permafrost and deep sea regions. Several big projects for gas hydrate research and exploration have been financed by Japan, India, Korea, China and the USA. It is assumed that the amount of carbon in natural gas hydrates is twice the amount present in oil, gas and coal together. This makes them interesting as a future energy source. To drill into horizontal layers filled with gas hydrates in the pores, directional wells are needed.

To achieve an adequate cutting transport, a high performance drilling fluid has to be used instead of sea water. The drilling fluid must be able to keep the gas hydrate reservoir stable while drilling and prevent the formation of secondary gas hydrates in the liquid. Moreover, the gas hydrate cuttings should not dissociate on their way to the surface. To avoid altering of the drilling fluid due to water and gas produced as a result of gas hydrate dissociation, cuttings should be kept stable to separate them from the fluid like any other rock cuttings by the surface equipment.

To prevent gas hydrate formation, thermodynamic inhibitors, like salt, glycols or methanol are used. Also, kinetic inhibitors are added to the drilling fluid to prevent gas hydrate agglomeration and formation for a period of time. Well known kinetic inhibitors are polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and polyvinylcaprolactam (PVCap).

Although ethylene glycol (EG) is seen as a thermodynamic inhibitor for gas hydrates, it is shown in this study that it is able to stabilize methane hydrate significantly. For the investigation, a high pressure cell with pressures up to 8.5 MPa was used. The equilibrium point of methane hydrate was detected. Solutions with PVP, PEG, hydroxyethylcellulose (HEC), Sodium dodecyl sulfate (SDS) and a kinetic inhibitor containing EG were tested (concentrations from 1 to 10 wt.‰). PVP, PEG and HEC could not stabilize gas hydrates at the test condition. SDS showed both a stabilizing and promoting effect. EG can significantly stabilize gas hydrates.
Numerical Simulation of Crushing and Bending Failure of Ice Using SPH
Authors: Das Jitapriya , Ehlers Sören
Published: October 2015

The primary objective of this investigation is to simulate bending and crushing failure of sea ice in a local scale using Smoothed Particle Hydrodynamics (SPH), which being a mesh free method offers a lot of advantages over traditional gridbased approaches. The numerical bending results are compared to earlier simulations of in-situ four-point bending test results and finite element simulations in terms of force, displacement and failure time whereas the crushing failure is compared with experiments conducted by Häusler. The comparison of these SPH-based numerical simulations with the available literature will serve as a basis to discuss the potential advantages and shortcomings of the mesh free particle method used to model failure of sea ice. Furthermore, this developed model will be extended further so as to simulate the actual behaviour of sea ice as ships progress through level ice.
Impacts of Cold Climate Environmental Conditions on a Riser System Design and Installation
Authors: Orimolade Adekunle Peter , Gudmestad Ove Tobias
Published: October 2015

Interests in exploration and production of oil and gas in cold climate areas has increased in recent times. This can be attributed to the continual depletion of reserves in mature fields, and recent discoveries of large quantities of oil and gas in the cold climate region, including the more recent discovery of the Alta Reservoir, in the Barents Sea. However, marine operations in this region are faced with challenges resulting from its arctic conditions.

Knowledge of the physical environment is important in designing offshore structures, and in planning, and executing marine operations. Selection of a suitable field development concept may be influenced by the probability of occurrence of rare events, such as drifting icebergs. Furthermore, occurrence of mesoscale phenomenon such as polar low pressures may adversely affect planned marine operations. In addition, uncertainties in weather forecasting will reflect on the available weather window to perform installation and interventions works.

This paper presents some of the challenges in designing and planning for marine operations in the cold climate region. A possible field development concept for the open water areas of the Norwegian sector of the Barents Sea is discussed. The current research work considers the need for further assessment of the probability of occurrence of drifting icebergs as of importance when selecting field development concept. The Floating Production Storage and Offloading (FPSO) is proposed, and this should be designed with an internal turret system that can be disconnected and reconnected. Some of the challenges associated with riser systems design when considering a turret system with the capability to disconnect and reconnect are discussed.

This paper also propose the use of ensemble forecasts as an alternative to the use of alpha factors to estimate operational weather window when planning for marine operations in the Barents Sea. The unpredictability nature of the environmental conditions, especially in the early winter is considered a challenge to marine operations.
Flexible Spools Solution for Hybrid Risers Base for Green Fields Developments
Authors: Tarbadar S. , Legeay S. , Bonnissel M. , Nossa O. , Karnikian A.
Published: October 2015

Rigid spools are commonly used at the riser base of hybrid riser systems such as STTRs (Single Top Tensioned Risers) or BHORs (Bundle Hybrid Offset Risers) for the deep water oil fields. Rigid spools design is critical and governed by numerous operating constraints such as dynamic loadings (due to motion of the vertical riser, Vortex Induced Vibration, slugging, etc.), soil properties and soil/spools/structures interaction.

Recent surveys on existing brown fields have highlighted unexpected issues on existing rigid spools. To solve these issues, an innovative flexible spool solution has been developed, combining unbonded flexible pipe structures in a “steep wave” configuration to accommodate the riser motions and FLET (Flowline End Termination) excursions avoiding soil deterioration and preventing unexpected spool behavior which could ultimately jeopardize its integrity.

A steep wave configuration solution can be introduced with distributed buoyancy over the flexible spools length. This design allows a direct connection between the riser base assembly and the flowline termination, solving the embedment issue and easing accommodation of the hybrid riser motions.

This paper describes the recent issues with rigid spools design and describes the solutions developed with flexible spool configurations to provide a more reliable riser base spools system for green fields.
Experimental Study on Wave and Wave-Current Loads on Vertical Surface-Piercing Column Structures
Authors: Lan Jian , Liu Zhen , Xianyu Chensong
Published: October 2015

Interactions between steep waves and a vertical surface-piercing cylinder as well as two cylinders in tandem arrangement with different spacings are investigated experimentally in this study. The focus of this study is on nonlinear wave and wave-current loads on structures. It is further aimed at investigating the higher harmonic loads and secondary loading cycle. The influence of non-dimensional parameters Kc, kA and Fr on the wave forces exerted on the structures is examined. The effect of spacing between two columns on the wave and wave-current loads is analyzed in depth. It is found that wave steepness plays an important role in the development of nonlinear wave force. It is also pointed out that the spacing effect on the nonlinear loading is rather pronounced.
Experimental Study on the Effect of Gas Hydrate Content on Heat Transfer
Authors: Meindinyo Remi-Erempagamo T. , Bøe Runar , Svartås Thor Martin , Bru Silje
Published: October 2015

Gas hydrates are the foremost flow assurance issue in deep water operations. Since heat transfer is a limiting factor in gas hydrate formation processes, a better understanding of its relation to hydrate formation is important.

This work presents findings from experimental study of the effect of gas hydrate content on heat transfer through a cylindrical wall. The experiments were carried out at temperature conditions similar to those encountered in flowlines in deep water conditions. Experiments were conducted on methane hydrate, Tetrahydrofuran hydrate, and ethylene oxide hydrate respectively in stirred cylindrical high pressure autoclave cells. Methane hydrate was formed at 90 bars (pressure), and 8°C, followed by a cooling/heating cycle in the range of 8°C → 4°C → 8°C. Tetrahydrofuran (THF) and ethylene oxide (EO) hydrates were formed at atmospheric pressure and system temperature of 1°C in contact with atmospheric air. This was followed by a heating/cooling cycle within the range of 1°C → 4°C → 1°C, since the hydrate equilibrium temperature of THF hydrate is 4.98°C in contact with air at atmospheric pressure. The experimental conditions of the latter hydrate formers were more controlled, given that both THF and EO are miscible with water.

We found in all cases a general trend of decreasing heat transfer coefficient of the cell content with increasing concentration of hydrate in the cell, indicating that hydrate formation creates a heat transfer barrier. The hydrate equilibrium temperature seemed to change with a change in the stoichiometric concentration of THF and EO. While the methane hydrate cooling/heating cycles were performed under quiescent conditions, the effect of stirring was investigated for the latter hydrate formers.
The Harmonic Polynomial Cell Method for Moving Bodies Immersed in a Cartesian Background Grid
Authors: Hanssen Finn-Christian W. , Greco Marilena , Shao Yanlin
Published: October 2015

In numerical simulations with moving bodies, and often with complex geometries, generation of high-quality body-fitted grids is a cumbersome and time-consuming task. An alternative is to use a fixed (Cartesian) background grid, and allow the body to move freely over this. The challenge in such methods is to transfer the body-boundary conditions of the moving body to fixed grid nodes in a rational manner. In this paper, an Immersed Boundary Method (IBM) is proposed to simulate potential flow about a moving body on a Cartesian background grid. The recently developed Harmonic Polynomial Method, proven both accurate and computationally efficient, is used to represent the velocity potential in the fluid. The body-boundary conditions are interpolated by using ghost nodes inside the body with mirror interpolation points in the fluid.

The method is first tested for a fixed cylinder in oscillatory flow to determine the accuracy of the proposed IBM, before considering the equivalent case of an oscillating cylinder in still fluid. Finally, a steadily-advancing cylinder is studied, which is considered as the most challenging case with respect to spurious pressure oscillations. These are known to be a challenge in many IBMs, and special attention is therefore devoted to this aspect.
CIP and Parallel Computing Based Numerical Solutions of 3-D Slamming Problems
Authors: Wen Peng , Qiu Wei
Published: October 2015

This paper presents the further development of numerical simulation method to solve 3-D highly non-linear slamming problems using parallel computing algorithms. The water entry problems are treated as multi-phase problems (solid, water and air) and governed by the Navier-Stokes (N-S) equations. They are solved by the three-dimensional constrained interpolation profile (CIP) method. The interfaces between different phases are captured using density functions. In the computation, the 3-D CIP method is employed for the advection phase of the N-S equations and a pressure-based algorithm is applied for the non-advection phase. The bi-conjugate gradient stabilized method (BiCGSTAB) is utilized to solve the linear equation systems. A Message Passing Interface (MPI) parallel computing scheme was implemented in the computations. For the parallel computations, the three-dimensional Cartesian decomposition of the computational domain was used. The speed-up performance of various decomposition schemes were studied.

Validation studies were carried out for the water entry of a 3-D wedge and a 3-D ship section with prescribed velocities. The computed slamming force, pressure distribution and free-surface elevations are compared with experimental results and numerical results by other methods.
HAM Solution of Nonlinear Wave Interaction With Uniform Current
Authors: Liu Zhen , Lin Zhiliang , Tao Longbin , Lan Jian , Kou Yufeng
Published: October 2015

The interaction of nonlinear progressive waves and uniform currents in water of finite depth is investigated analytically by means of the homotopy analysis method (HAM). In the HAM, the velocity potential of the wave is expressed by Fourier series and the nonlinear free surface boundary conditions are satisfied by continuous mapping. The present approach does not depend on any small parameters, thus the solutions are suitable for steep waves and strong currents. To verify the HAM solutions, experiments are conducted in wave-current flume of Education Ministry Key Laboratory of Hydrodynamics at SJTU. It is shown that the HAM solutions are in good agreement with experimental measurements. The present study demonstrated that the great potential of the HAM to solve more complex wave-current interaction problems leading to engineering applications in traditional offshore industry and marine renewable energy sector.
Transducer Qualification for Wave Impact Load Measurements Using Wedge Drop Tests
Authors: Huang Zhenjia (Jerry) , Oberlies Robert , Spencer Don , Kim Jang
Published: October 2015

For the design of offshore structures in harsh wave environments, it is essential to accurately determine the wave impact loads on the structure. To date, robust numerical prediction methods / algorithms for determining wave impact forces on offshore structures do not exist. Model testing continues to be the industry practice for determining wave impact forces on offshore structures. Accurate measurements of wave impact loads in model tests have been challenging for several decades. Transducers require the ability to capture the short duration, dynamic nature and high magnitude of impact loads. In order to qualify transducers for these types of measurements, we need to develop a way to physically impose dynamic impact loads on the transducers and to establish benchmark values that can be used to check the effectiveness of their measurements. In this paper, we present our recent research work on transducer qualification for wave impact load measurements, including their development, numerical analysis and wedge drop model tests. Our findings show that wedge drop tests can be used to impose dynamic impact loads for transducer qualification, and that the Wagner solution and / or validated computational fluid dynamics (CFD) simulations that include the effects of viscosity, compressibility and hydroelasticity can provide the appropriate benchmarking values. Numerical simulation results, model test measurements and findings on transducer qualification are presented and discussed in the paper.
Numerical Investigation of the Influences of Fishing Net on Waves
Authors: Zhao Yunpeng , Bi Chunwei , Dong Guohai , Chen Changping , Li Yucheng
Published: October 2015

A two-dimensional numerical wave flume is established based on the finite-volume method. The movement border method is adopted as a wave generator at one end of the flume. The volume of fluid (VOF) method is used to track the wave surface. In the numerical simulation, the plane net is simplified as porous-media model. The coefficients of the porous media are determined by the least squares method. In this way, the porous-media model will has the same pressure drop with the fishing net. To validate the numerical model, the numerical results are compared with the data obtained from corresponding physical model tests. It is found that the numerical results are in good agreement with the corresponding experimental data. Using the proposed numerical model, wave propagation through a plane net with different net solidities, different attack angles as well as two nets with different spacing distances are investigated. The impacts of the wave height and wavelength on the wave propagation through the plane net are also discussed.
Experimental Studies of Hydrodynamic Interaction of Two Bodies in Waves
Authors: Zhou Quan , Liu Ming , Peng Heather , Qiu Wei
Published: October 2015

There are challenges in the prediction of low-frequency load and especially the resonant free surface elevation between two bodies in close proximity. Most of the linear potential-flow based seakeeping programs currently used by the industry over-predict the free surface elevation between the vessels/bodies and hence the low-frequency loadings on the hulls. Various methods, such as the lid technique, have been developed to suppress the unrealistic values of low-frequency forces by introducing artificial damping coefficients. However, without the experimental data, it is challenging to specify the coefficients.

This paper presents the experimental studies of motions of two bodies with various gaps and the wave elevations between bodies. Model tests were performed at the towing tank of Memorial University. The objective was to provide benchmark data for further numerical studies of the viscous effect on the free surface predictions. The experimental data were compared with numerical solutions based on potential flow methods. The effect of tank walls were examined. Preliminary uncertainty analysis was also carried out.
Analysis of Ice Accretion on Vertical Surfaces of Marine Vessels and Structures in Arctic Conditions
Authors: Dehghani-sanij Alireza , Muzychka Yuri S. , Naterer Greg F.
Published: October 2015

The phenomenon of icing in cold climates is a challenging problem of engineering analysis, which involves heat transfer, phase change and multiphase flow with water droplets. This phenomenon has an important impact on the performance and operation of marine vessels, offshore structures, and others such as wind turbines, power lines, and aircraft surfaces. In this paper, a predictive icing model for large vertical surfaces of a marine vessel is developed theoretically. The total flux of sea-spray, including wave spray and wind spray, is analyzed during the spray process. By using heat, mass and salt concentration balances, the freezing fraction, temperature distribution, ice layer thickness, and liquid film thickness are determined. The results are compared with the numerical and experimental results of other studies. Good agreement between the theoretical predictions and other results demonstrates the improved accuracy of the proposed method over past models.
Issues in Welding Residual Stress Model in Fitness for Service Assessment of Crack-Like Defect in Weld Area
Authors: Hong Jeong K. (J. K.) , Brodzinski Richard P. , Vargas Pedro M. , Rhee H. Chong , Young K-John , Penso Jorge A.
Published: October 2015

Current Industry Code and Standard (ICS) Fitness for Service Assessment (FFSA) procedures for crack-like defect in weld area tend to impose high level of conservatism. In addition to the necessity for using conservative Welding Residual Stress (WRS) model due to the uncertainty inherent in the WRS estimation, using the original WRS regardless of crack depth in the crack driving force calculation, like the applied operating load, is the primary reason for this solution conservatism. In addition, current ICS weld area defect assessment procedures involve ambiguities in boundary condition effects on WRS models, as well as in the fracture mode of weld area crack being treated in the context of opening mode only, even though there is no weld area geometric symmetry essential for precluding fracture modes other than mode I.

To clarify these technical issues in the ICS FFSA practices rigorous numerical simulation analyses of welding process and crack growth following joint fabrication have been performed, using the finite element analysis procedure. A crack driving force calculation procedure for weld area cracks, which was developed to quantify the crack extension effects on WRS for growing crack, was used for the finite element crack growth simulation analyses. The rigorous finite element analysis results for boundary condition effects on WRS, the fracture mode of weld toe crack, and crack growth effects on crack driving force parameters caused by WRS are compared with those of current ICS solutions. These comparisons demonstrate the need for an improvement of the current ICS FFSA procedures for weld area crack-like defects.

The primary objective of the present paper is to motivate the industry to improve ICS FFSA procedures by clarifying these ambiguous technical issues in weld area crack-like defect assessment parameters, as well as considering crack extension effects on WRS properly in calculating the crack driving force of growing crack to reduce undue conservatism in FFSA.
Reliability Analysis and Design for Pipe-in-Pipe Pipelines With Centralizers
Authors: Mao Steve , Kamal Muhammad , Qiao Wei , Dong Gang , Duffy Brian
Published: October 2015

In this paper, a simplified reliability model is developed to identify how the pipe-in-pipe component uncertainties (manufacturing tolerances of centralizer thickness) influence the fatigue life of the system. The focus is on the reliability analysis with respect to the centralizer thickness. In order to reduce the complexity of the problem, only the centralizer thickness is considered to be a random variable. A limit function is formulated based on the three dimension (3D) finite element analysis. With the help of the probabilistic method, the correlation between the centralizer thickness and the failure probability is investigated. Two examples on pipe-in-pipe pipeline system are analyzed. The first one presents the relationship between centralizer thickness and failure probability for inner and outer pipes. The second one is an application of six mile pipe-in-pipe pipeline system. The failure probability of the fatigue is estimated. The influence of the centralizer thickness decreasing with time due to the abrasion, creep wear and elastic deformation is also considered when computing fatigue life and failure probability. The maximum fatigue damage ratio is calculated based on all trial samples generated considering manufacturing tolerances. If the maximum fatigue damage ratio is less than or equal to the allowable fatigue damage ratio, the failure probabilities with respect to the given centralizer thickness is negligible and the design is acceptable if only considering the influence of the given centralizer thickness. In addition, numerical results show that the maximum fatigue damage ratio possibly exceeds the allowable fatigue damage ratio considering manufacturing tolerances although the deterministic fatigue damage ratio is less than the allowable fatigue damage ratio.
Updating of Probabilistic Corrosion Model Based on Bayesian Procedure
Authors: Yamamoto Norio
Published: October 2015

Corrosion condition is predicted based on the corrosion model. The corrosion model is necessary to be identified according to the corrosion data collected from the various vessels because corrosion phenomenon is stochastic. However, in order to predict corrosion condition of one specific vessel, such corrosion model is necessary to be modified to reflect the effect of specific corrosion environment of the subject vessel.

In the study, procedure of updating corrosion model was investigated based on Bayesian inference on the parameters in the probabilistic corrosion model which utilizes the thickness measurements data. The developed procedure was demonstrated by the application of actual thickness measurements data of the vessel. Even though the amount of corrosion data was limited, the corrosion prediction model was well updated which could be verified by the concentration of posterior distribution which shows the degree of belief on the parameters in the probabilistic corrosion model. The estimated distributions of coating life and corrosion wastage were compared with the frequency distributions obtained by the corrosion data. The estimated distributions of coating life and corrosion wastage showed good agreement with the frequency distributions obtained by the corrosion data.
Interaction of Ice Force in Ship-Ship Collision
Authors: Nelis Sander , Tabri Kristjan , Kujala Pentti
Published: October 2015

The maritime transportation system in the Northern Baltic Sea (NBS) is complex and operates under varying environmental conditions. The most challenging conditions relate to the presence of ice-cover, which for the NBS e.g. for the Gulf of Finland or Bay of Bothnia, can remain up to several months. The number of maritime accidents in these two areas is the highest during winter season, which can involve accidents like groundings, collisions, damages due to the ice etc. The paper presents the model to predict the ice interaction in ship-ship collision dynamics. The ice forces are included in the time-domain simulation model and also in a simplified model based on the momentum conservation. The simplified model is proposed for a rapid estimation of increase in deformation energy due to the presence of ice forces. The analysis shows that the ice influence depends strongly on the ship mass, ice thickness and collision speed. The maximum increase in the deformation energy in the studied collision scenarios was up to 19%.
Modelling of Pressure Fluctuations in a Wellbore While Tripping
Authors: Tarasevich Vladimir , Podryabinkin Evgeny , Bocharov Oleg , May Roland
Published: October 2015

Assembling or dismantling drillstring sections during tripping operations results in a periodically accelerated or decelerated motion of the drillstring in the borehole. While running in or pulling out of hole the drillstring induces a flow of displaced fluid and a pressure change in the borehole. These pressure changes can be divided into two components: First, the “steady” pressure change associated with the mud viscous friction; and second, the pressure fluctuations caused by induced acceleration of the drilling fluid. Pressure surges are especially dangerous for the uncased well sections and at the bottom of the well, because they can damage and destroy the wellbore. The accurate prediction of pressure fluctuations is significant for wells where the pressure must be maintained within a narrow range to enable safe drilling and completion of the well. Sudden pressure changes in such wells may lead to the so-called water-hammer effect that can be observed in wells when pump operation modes change or when the string is accelerated. A large-scale water-hammer effect may damage the uncased section of a well, leading to fractures or formation fluid inflow.

The objective of this paper is to estimate the magnitude of the pressure surges caused by accelerated movement of the drillstring. A mathematical model was formulated to describe the unsteady behavior of flow rate and pressure change along the well. The model involves a one-dimensional system of equations, which are a modification of the equations for hydraulic shocks in the annulus, and the cylindrical part of a well.

When frictional losses are neglected, it is possible to derive an exact analytical solution of the problem. This analytical solution was used to estimate the maximum and minimum pressure in the borehole.

When combined with the methods for frictional pressure losses, the suggested method can predict the pressure change in a wellbore while tripping. Newtonian and power law fluids were considered for the parameter study.
Assessment of Statistical and Hybrid LES Turbulence Closures for Surface Combatant DTMB5415 at 20° Static Drift Condition
Authors: Visonneau Michel , Guilmineau Emmanuel , Wackers Jeroen , Deng GanBo , Queutey Patrick
Published: October 2015

This paper provides detailed validation of the complex free-surface flow around the surface combatant DTMB5415 at 20° static drift conditions. Particular emphasis is being placed on the onset and progression of the various vortical structures created at the sonar dome, at the free-surface and around bilge keels in conditions where free-surface breaking may occur. A detailed analysis of this complex free-surface flow is conducted on grids which are dynamically refined to capture the vortical structures. Local comparisons with recent experiments performed at the Iowa Institute of Hydraulic Research (IIHR) during a joint NATO-AVT (Advanced Vehicle Technologies) collaboration are used to perform detailed flow analysis and draw some conclusions about the actual potentialities of advanced Computation Fluid Dynamics (CFD) method in terms of physical and numerical modeling.
Lessons Learned From Deepwater-Spool Design on Aasta Hansteen
Authors: Jacobsen Tore , Norland Kristian , Tharigopula Venkatapathi
Published: October 2015

Spools are frequently used to tie-in pipelines to subsea structures with the purpose of absorbing expansions at the pipeline end, in addition to the connection between pipeline and structure. Deepwater rigid spools have to be designed to accommodate expansion movements resulting from high product temperatures, low strength soils and phenomena such as pipe walking. They also have to accommodate spool fabrication and installation tolerances. These requirements drive the spool geometry and can lead to complex spool geometries that are difficult to install.

The design code usually used for spool analysis is DNV-OS-F-101 [1] which is a primary design code for pipeline design. While using this design code for straight-linepipe and bends, careful considerations should be made because the bends tend to behave different from a straight pipe. Especially the ovality response under in-plane bending is of interest for establishment of a design criteria. The most accurate way to establish this design criteria is by utilising a 3-D non-linear finite element (FE) analysis. The bending moment at failure should be compared with the corresponding bending moment under design conditions. By using FE analyses, more flexible spool can be designed giving lower reaction forces and moments. In addition there are other design-optimization methods to reduce the required spool size and complexity which are further described in this paper. The present paper shows the reduction in wall thickness that is possible through design by analyses. The spool design process is also outlined, and a comparison made on different spool size optimization concepts.
Control of an Open-Loop Hydraulic Offshore Wind Turbine Using a Variable-Area Orifice
Authors: Buhagiar Daniel , Sant Tonio , Bugeja Marvin K.
Published: October 2015

The viability of offshore wind turbines is presently affected by a number of technical issues pertaining to the gearbox and power electronic components. Current work is considering the possibility of replacing the generator, gearbox and electrical transmission with a hydraulic system. Efficiency of the hydraulic transmission is around 90% for the selected geometries, which is comparable to the 94% expected for conventional wind turbines. A rotor-driven pump pressurises seawater that is transmitted across a large pipeline to a centralised generator platform. Hydroelectric energy conversion takes place in Pelton turbine. However, unlike conventional hydro-energy plants, the head available at the nozzle entry is highly unsteady. Adequate active control at the nozzle is therefore crucial in maintaining a fixed line pressure and an optimum Pelton turbine operation at synchronous speed. This paper presents a novel control scheme that is based on the combination of proportional feedback control and feed forward compensation on a variable area nozzle. Transient domain simulation results are presented for a Pelton wheel supplied by sea water from an offshore wind turbine-driven pump across a 10 km pipeline.