bluuebunny/crossref_metadata_2025 huggingface dataset:
Model-Scale/Full-Scale Correlation of NRC-OCRE’s Model Resistance, Propulsion and Maneuvering Test Results
Authors: Lau Michael
Published: October 2015

There are a variety of model ices and test techniques adopted by model test facilities. Most often, the clients would ask: “How well can you predict the full scale performance from your model test results?” Model-scale/full-scale correlation becomes an important litmus test to validate a model test technique and its results. This paper summarizes the model-scale/full-scale correlation performed on model test data generated at the National Research Council - Ocean, Coastal, and River Engineering’s (NRC-OCRE) test facility in St. John’s. This correlation includes ship performance predictions, i.e., resistance, propulsion and maneuvering. Selected works from NRC-OCRE on the USCGC icebreaker Healy, the CCGS icebreaker Terry-Fox, the CCGS R-Class icebreakers Pierre Radisson and Sir John Franklin and the CCGS icebreaker Louis S. St. Laurent were reviewed and summarized. The model tests were conducted at NRC-OCRE’s ice tank with the correct density (CD) EGADS model ice. This correlation is based on the concept that a “correlation friction coefficient” (CFC) can be used to predict full-scale ship icebreaking resistance from model test data. The CFCs have been compared for correlation studies using good-quality full-scale information for the five icebreaker models in the NRC-OCRE’s model test database. The review has shown a good agreement between NRCOCRE’s model test predictions and full-scale measurements.

The resistance and power correlation were performed for five sets of full-scale data. Although there is substantial uncertainty on ice thickness and ice strength within the full scale data sets that contributes to data scattering, the data suggest a conservative estimate can be obtained to address reasonably this uncertainty by increasing the model prediction by 15% that envelopes most data points.

Limited correlation for maneuvering in ice was performed for the USCGC icebreaker Healy. Selected test conditions from the sea trials were duplicated for the maneuvering tests and turning diameters were measured from the arcs of partial circles made in the ice tank. Performance predictions were then compared to the full-scale data previously collected. Despite some discrepancy in ice strength and power level between the model tests and sea trial, the model data agree well with the sea trial data except for three outliers. Otherwise, the maneuvering data show a good correlation between the model test and sea trial results.
Quantification of Risks Associated With a Representative Production Well in the Gulf of Mexico
Authors: Zulqarnain Muhammad , Tyagi Mayank
Published: October 2015

After Macondo incident a great effort is under way to improve the safety of deepwater drilling and production operations and enhance the capabilities of different well barrier to stop the oil spill on its earliest stages. This study is a part of that collective effort to make offshore operations safe and decrease the associated risks. The main objective of this study is to quantify and categorize the risk associated with a representative well in the Gulf of Mexico during its normal production operations. In order to achieve an appropriate balance between safety and economics of deepwater oil and gas operations, Quantitative Risk Assessment (QRA) techniques can be successfully used. Quantified risk is computed from the product of blowout frequency and volume of oil spilled as a consequence. Blowout frequency is calculated from Fault Tree Analysis (FTA) and spilled oil volume is estimated from simulating multiphase fluid flow and heat transfer in wellbores.

A large number wells are completed with some sort of bottom hole sand control elements to prevent production of sand. The failure of these control elements may have severe consequence and in some cases may result in uncontrolled hydrocarbon flow to the environment as well. A representative production well from the Mississippi Canyon in the Gulf of Mexico is selected for the for quantitative risk assessment (QRA) analysis. The well is completed with cased hole gravel pack and with sand control elements in place. The representative reservoir properties for this well are selected from the literature and uncertainties in properties are accounted for by fitting lognormal distribution and carrying out Monte Carlo simulations. P50 value for the reservoir properties from Monte Carlo simulation is used to find worst case discharge rates by using a commercially available multiphase flow simulator with black oil model.

A Fault Tree is constructed to find the blowout probability based on the equipment failure data. From the minimal cut set method the importance and sensitivity of different well barrier is analyzed and most important areas to focus on are identified. The analysis showed that the constructed fault tree is most sensitive to sand screen failures, followed by subsea production tree and delayed response to a situation of immediate concern.
Wave-Current Interactions in a Marine Current Turbine Using ANSYS FLUENT CFD
Authors: Singh Amit , Arockiasamy Madasamy
Published: October 2015

This paper presents the results of the study on the wavecurrent interactions of an idealized full scale marine current turbine (MCT). A multi-phase flow model is used for simulation of three cases: still water and two different wave heights. The Standard k-ω turbulence model is chosen based on the stability of the pressure and velocity plots upstream and downstream the turbine rotor plane. The three cases are used in the present study to compare the effects of wave height and current velocity on the turbine rotor. The velocity, and pressures on the turbine blades are computed for each case using ANSYS FLUENT CFD Software. The thrust, torque, and power in the MCT are calculated using the results obtained from the CFD simulation.

The turbine rotor blades are drafted in 3D using SolidWorks by extruding cross sections of a 43.2 m diameter turbine blade published by the National Renewable Energy Laboratory (NREL). Tetrahedral mesh elements are used to represent the multiphase fluid domain and rotor blades in ANSYS ICEM CFD due to its simplicity and speed of computation. The ANSYS FLUENT simulation is set up to run air and water phases in the domain, while the rotor blade is suspended in the fluid domain, such that there is 20 m of water in front and 100 m behind the plane of rotation. The effects of varying wave heights on the thrust, torque, and power are presented based on the tip speed ratios. The power generated by the turbine rotor from the wave cases is found to be higher than those for the still water case, at lower current velocities. However, at current velocities higher than 2.00 m/s, the power generated from the still water case is higher than the wave cases. At lower tip speed ratios, the thrust on the turbine, subjected to wave conditions, is lower than that for the still water condition. At higher tip speed ratios, the thrust on the turbine, under wave conditions, is higher than that for the still water condition. The torque decreases exponentially with increases in the tip speed ratio for all three cases, but the torque remains nearly constant with increases in wave height. The results provide detailed information which would be valuable in the design and operation of marine current turbines in wave environments.
Experimental Investigation of Fish Farm Hydrodynamic Wake Properties on 1:15 Scale Model Circular Aquaculture Cages
Authors: Turner Adam A. , Jeans Tiger L. , Reid Gregor K.
Published: October 2015

Hydrodynamic experiments on 1:15 scale model arrays of circular fish cages, typically used in eastern Canada, have been completed in the recirculating flume tank located at the Fisheries and Marine Institute of Memorial University in St. Johns, Newfoundland. Scale model cages were designed with a high amount of detail from 100 m circumference cages used in industry. Two different cage spacings were tested, representing spacing of cages typically found at cage sites. A global force ratio scaling technique was developed and applied to the experiment to ensure geometric similarity between cages of model scale and full scale. Planes of 64 (8×8) wake velocity measurements at both cage spacings were taken behind individual cages within the array and at distances in the wake of the entire array, to observe velocity deficits, wake topology, wake recovery and unsteadiness in the flow field. Results show high velocity deficits behind the cages, causing accelerations in the flow underneath and around the sides of the cages. High amounts of unsteadiness is found to be generated at the bottom of the cages due to the presence of a shear layer in the wake of the cages. Dye release was also used to observe many features of the flow field at one time, and to verify results obtained from wake velocity measurements.
Comparison of Numerical Methods for Strain Based ECA
Authors: Navarro Josef , Low Andrew , Tran Thao (Joe)
Published: October 2015

The integrity of subsea pipe girth welds is routinely ensured through Engineering Criticality Assessments (ECAs) based on fracture mechanics principles. In order to capture the whole design life, the ECA must cover loadings that the pipeline is subjected to during both installation and operation.

Stress based semi-analytical methods using Failure Assessment Diagrams (FAD) have been used extensively for ‘run of the mill’ assessments as far as C-Mn steel pipe with overmatching weld is concerned. These stress based methods are captured in depth in industry codes such as BS7910 and DNV-OS-F101.

In recent years however, with industry seeking to transport more corrosive fluids, the use of pipe containing a corrosion resistant alloy (CRA) layer is becoming increasingly popular. Together with the CRA layer, anti-corrosion weld consumables material would be used at the pipe joints to protect the whole pipeline from corrosion. Some of these weld consumables, especially at high temperature, partially overmatch or even undermatch the parent pipe material, resulting in difficulties in application of conventional FAD approach. Industry has turned to numerical methods to fill in gaps which are not covered by the FAD based approach. However no codified approach/standard exists for executing numerically based ECAs.

This paper attempts to outline the FAD and numerical approaches being used by industry. The different approaches will be assessed for their range of application, limitations of execution and comparison of results obtained. The study is carried out for the case of a typical external surface flaw in a 12″ pipe.
On Optimal Method of Mooring Ship in Floating Tsunami Protection Wharf
Authors: Masuda Koichi , Masuda Mitsuhiro , Minami Kiyokazu , Ikoma Tomoki
Published: October 2015

On the vessels moored the quay, the situation such as drifting and runs on the quay due to the breaking of the mooring lines is generated by the tsunami. The authors are clarified for applicability of the proposed floating tsunami protection wharf (FTPW) and install more mooring tether. The effect of FTPW is most promising as disaster prevention and mitigation measures for the vessels moored quay, but exert a sufficient effect in the transverse tsunami incident, but the effect cannot be confirmed in the longitudinal tsunami incident. Therefore, it is necessary to go in combination in FTPW and tsunami countermeasures in consideration of the longitudinal tsunami incident, such as install more mooring tether and new mooring method. The objectives of present study are to consider valid mooring method for longitudinal tsunami incident and also to propose a tsunami most effective countermeasure of wharf mooring vessel.
Virtual Spring-Damping System for Flow Induced Motion Experiments
Authors: Sun Hai , Bernitsas Marinos P. , Kim Eun Soo , Bernitsas Michael M.
Published: October 2015

The research objective of the Marine Renewable Energy Lab (MRELab) is to design multi-cylinder VIVACE Converters and optimize their power output for a broad range of velocities. For a given geometric and mass configuration of a school of cylinders, each point on the power envelope, at a given flow-speed, is a function of the spring constant and damping. Conducting tests with real springs and dampers requires lengthy preparation for each set of experiments. A more efficient way to conduct experiments faster and accurately is developed based on a controller embedded virtual spring-damping system (Vck) that des not include the hydrodynamic force in the closed loop. Each oscillator consists of one Vck, one interchangeable cylinder moving on submerged roller blocks and driven by the fluid flow, and connected to the controller through belts and pulleys. It is designed to achieve the desired static/dynamic friction through the Vck. An Arduino embedded board controls a servomotor with an optical encoder, which enables real-time position/speed measurement. A system identification (SI) methodology is developed making possible to identify the damping model of any oscillator, which is typically much more complicated than the classical linear viscous model. Upon completion of the SI process for an oscillator, the actual nonlinear damping model is subtracted using the controller and leaving the system with zero damping. Then, a mathematically linear damping model is added, thus, resulting in a system with real linear viscous damping. This process enables changing the spring constant and harnessing damping through the controller instantly. Experiments are then conducted with both real spring dampers and Vck to validate the process. All FIM experiments are conducted in the Low Turbulence Free Surface Water Channel of the University of Michigan at 16,000<Re<140,000.

The main findings are: (a) The Vck system was developed keeping the hydrodynamic force out of the control loop and, thus, not biasing the FIM. (b) The agreement between real and virtual springs and dampers was excellent in FIM measurements over the entire range of spring constants and velocities tested. (c) The lag due to the controller was minimal and significantly reduced compared to the first generation of Vck built in the MRELab.
Methodology to Evaluate Sea Ice Loads for Seasonal Operations
Authors: Thijssen Jan , Fuglem Mark
Published: October 2015

Offshore structures designed for operation in regions where sea ice is present will include a sea ice load component in their environmental loading assessment. Typically ice loads of interest are for 10−2, 10−3 or 10−4 annual probability of exceedance (APE) levels, with appropriate factoring to the required safety level.

The ISO 19906 standard recommends methods to determine global sea ice loads on vertical structures, where crushing is the predominant failure mode. Fitted coefficients are proposed for both Arctic and Sub-Arctic (e.g. Baltic) conditions. With the extreme ice thickness expected at the site of interest, an annual global sea ice load can be derived deterministically. Although the simplicity of the proposed relation provides quick design load estimates, it lacks accuracy because the only dependencies are structure width, ice thickness and provided coefficients; no consideration is given to site-specific sea ice conditions and the corresponding exposure. Additionally, no term is provided for including ice management in the design load basis.

This paper presents a probabilistic methodology to modify the deterministic ISO 19906 relations for determining global and local first-year sea ice loads on vertical structures. The presented methodology is based on the same ice pressure data as presented in ISO 19906, but accounts better for the influence of ice exposure, ice management and site-specific sea ice data. This is especially beneficial for ice load analyses of seasonal operations where exposure to sea ice is limited, and only thinner ice is encountered. Sea ice chart data can provide site-specific model inputs such as ice thickness estimates and partial concentrations, from which corresponding global load exceedance curves are generated. Example scenarios show dependencies of design loads on season length, structural geometry and sea ice conditions. Example results are also provided, showing dependency of design loads on the number of operation days after freeze-up, providing useful information for extending the drilling season of MODUs after freeze-up occurs.
Experimental Reconstruction of the Hull Sectional Forces Under Slamming Events
Authors: Dessi Daniele
Published: October 2015

An analysis of the slamming load distribution along a slender floating body on the basis of experimental measurements is presented. The dataset is provided by the (lumped) vertical forces measured on the hull portions of a segmented scaled model in seakeeping tests. Using the proper orthogonal decomposition the vector time-history of the hydrodynamic forces is first decomposed into the summation of few terms, each one retaining separately time and space information. This decomposition allows highlighting interesting features regarding variations in the load distribution under different test conditions. The analysis has exploited also the use of pre-filtering for separating the load components at different frequencies to be further decomposed with POD. Then, a polynomial spline approximation under integral constraints is used to approximate the shape functions and then to obtain the continuous distribution of the sectional force. The considered tests were carried out in both irregular sea and regular waves with a choice of model speed and wave parameters so as slamming occurs. The identified distribution of force per unit length over the impacting hull segments is then compared with a modified Von-Karman model (with 3D correction) which accounts for the water uprise in the expression of the slamming force and variable entry velocity.
Vessel Performance Analysis and Fuel Management
Authors: Mak Lawrence , Seo Dong Cheol , Kuczora Andrew , Sullivan Michael
Published: October 2015

A prototype Vessel Performance Monitoring and Analysis System (VPMAS) was deployed on a ferry to acquire needed performance data, to help improve vessel performance and reduce fuel consumption. A paper published in 2014 described preliminary data trends observed, key performance indicators computed, data products explored and exploratory tools developed for crews to gain insight into their vessel operation. The current paper describes further analysis of the operational data for speed optimization in calm sea states and the preliminary development of trim optimization software.

It was found that trip durations around 7 hours (13.3 knots) use the least amount of fuel. The least amount of fuel is used when the excess distance travelled is minimized and the voyage time is optimized. There is a lot of leeway in terms of voyage time and excess distance travel by the ship before there is a heavy penalty on fuel consumption. Considering only a mean draft of 6 m and an average speed of 14 knots in the current paper, the optimal trim condition for the ferry is around −0.6 m (bow down), which reduces the resistance by 15% compared to the even keel condition. Positive trim causes the considerable increase of the total resistance consistently.
Mobile Data Collection
Authors: Lugo David , Ortega Juan
Published: October 2015

A key process in the oil industry to make decisions is data collection. To improve productivity it is important data and information analysis. For many organizations is not profitable data automation, which has an impact in the way organizations, collect data. Data collection is taken by manual processes that create uncertainty for analysis because it is not reliable. As consequence, making a decision has not the planned results. After working for many years in the oil industry was identified:

1. People collecting data in a manual process normally by using a piece of paper which could be lost or damage.

2. After taking data at the well, data are brought to the office. Then, data are downloaded by another worker in computer software. It can be modified intentionally or not.

3. Accuracy of data collection activity is carried out. How do we know if the staff really went to work area?

4. Training to new staff, lack of experience?

5. There are “risks zones” due vandalism, facilities are damaged by people who stole devices which causes great money losses to companies.

All these mentioned factors affect decision making which has a big impact in the production process. This application helps the whole process from collection data until data are registered in databases.

This application considered several observations, suggestions and comments from people involve in the oil industry, especially at the production area. As a result, it is a tool that support data collection, standardize information in databases, improve data quality (it doesn’t matter localization), shows time and photographic position in a mobile device.

Information is generated digitally taking advantage of easy handling.

To summarize advantages of the whole system:

• Reduce time of the data re-collection process

• Improve data quality

• Reduce amount of people working on data registration

• Data reliability

• Support decisions making

• Minimize the use of paper in order to help ambient environment

• Improve vehicle logistics

• Minimize use of gasoline which helps to reduce costs

• Help to optimize routes for vehicles on the field

• Productivity, Maintenance, etc., reports can be generated

• Vandalism is not a problem
Methods for Establishing Governing Deck Impact Loads in Irregular Waves
Authors: Birknes-Berg Jørn , Johannessen Thomas Berge
Published: October 2015

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which previously have had sufficient clearance between the deck and the surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. The accurate calculation of deck impact loads with a prescribed probability of occurrence taking into account the relevant properties of the incident waves, presents a considerable challenge.

The ShorTCrest JIP has addressed both the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It has been concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory /5/.

The present paper investigates a simple method to calculate deck impact loads in irregular waves which take into account the irregularity of the sea state and the possibility of wave breaking. The method is a two-step approach. Firstly, a long duration simulation of surface elevation is carried out using second-order theory in order to identify possible deck impact events. The individual wave events which are capable of impacting the deck is then reproduced using a CFD method and the distribution of the deck impact loads is established.

The calculations are compared with model test results for wave impact with a large volume deck box in a single steep sea state and with CFD calculations of deck impact with regular waves.
Water Intake Riser Model Test and Numerical Calibration
Authors: Xiang Sherry , Cao Peimin , He Jingxi , Kibbee Steve , Bian Sean
Published: October 2015

A model test campaign of a large diameter water intake riser (WIR) has been planned, designed, and successfully executed in an offshore model basin. The objective of the model test is to better understand the global dynamic behavior of WIR, and thus advance its design. The scopes of the model test are to measure the response of the riser under floater motions; investigate the effect of the internal water and flow rate; and observe any vortex-induced-vibration (VIV) and axial instability due to motion and / or internal flow.

The paper presents the model test results and the numerical calibrations and validations. The WIR pipe was carefully scaled and designed to meet the test objectives. The WIR in model test scale is 150 mm in inside diameter and approximately 36 m in length. The model test setup includes a fully instrumented riser, a planar motion mechanism (PMM) which simulates the vessel motion and an internal water flow system (IWFS). The riser was instrumented with Fiber Bragg Grating (FBG) strain sensors along the pipe length and circumference. The WIR was hung-off from the PMM inside the deep basin pit. More than 200 cases were carried out in the basin including the sinusoidal motion tests and random motion tests with different flow rates.

The model tests collected a wealth of data of the WIR dynamic responses under the vessel motions and the internal water flow conditions. As expected, WIR global bending responses are highly dependent on the pipe excitation modes and their corresponding mode curvatures. These responses can be predicted well by numerical software through a calibration process. The axial response of WIR due to motion and/or internal flow is much more complex. The amount of internal water coupled with the pipe depends on the vessel motions and internal flow fluctuation. This is important for axial stability prediction and seawater lift system design.
Experimental and Numerical Investigations of Bubble Dynamics in Porous and Non-Porous Media
Authors: Rahman M. A. , Butt S. , Alam J. M. , Shahwan M. , Hunt M. , Imtiaz S.
Published: October 2015

In this study an experimental work is conducted to investigate the shape and speed of an air bubble in a pipe filled with different viscous fluids and porous media. The experimental results are also compared with the Computational Fluid Dynamics (CFD) simulation. Multiphase flows are complex due to the infinitely deformable nature of interface in gas/liquid flows. If one of the phases is gas acts as dispersed phase in the form of bubble, then the complexity will arise from the non-uniform distribution of bubbles in the pipe cross-section and axial distance. Inclusion of different viscous fluids simulating the industrial scale hydrocarbon properties brings added challenge in understating the bubble rise, coalescence and breakup dynamics. Moreover, bubble rise and change of shape of bubble in porous media will bring additional complexity in the flow dynamics. The pipe used in the experiment and CFD was 11.6 cm ID and a length of 100 cm. Three situations were tested: i) an air bubble rising in stagnant water, ii) an air bubble rising in moving water, and iii) an air bubble rising in a stagnant water but filled with porous media with porosity of 27%. Preliminary CFD results indicate that an air bubble has an average velocity of 0.2468 m/s and 0.2524 m/s in stagnant water and moving water, respectively, which is very close to experimental results.
Coupled Heat and Mass Transfer CFD Model for Methane Hydrate
Authors: Neto Eugenio Turco , Rahman M. A. , Imtiaz Syed , Pereira Thiago dos Santos , Sousa Fernanda Soares de
Published: October 2015

The gas hydrates problem has been growing in offshore deep water condition where due to low temperature and high pressure hydrate formation becomes more favorable. Several studies have been done to predict the influence of gas hydrate formation in natural gas flow pipeline. However, the effects of multiphase hydrodynamic properties on hydrate formation are missing in these studies. The use of CFD to simulate gas hydrate formation can overcome this gap. In this study a computational fluid dynamics (CFD) model has been developed for mass, heat and momentum transfer for better understanding natural gas hydrate formation and its migration into the pipelines using ANSYS CFX-14. The problem considered in this study is a three-dimensional multiphase-flow model based on Simon Lo (2003) study, which considered the oil-dominant flow in a pipeline with hydrate formation around water droplets dispersed into the oil phase. The results obtained in this study will be useful in designing a multiphase flow metering and a pump to overcome the pressure drop caused by hydrate formation in multiphase petroleum production.
Parametric Study of the VIM Response of Submersible Buoy of the FSHR System
Authors: Tsukada Raphael I. , Pereira Natalia V. , Flora Bruno , Shiguemoto Denis A.
Published: October 2015

Nowadays, hybrid risers systems have been continuously adopted for deep and ultra-deep water petroleum fields. This riser system consists of a submersible buoy connected to flexible and rigid risers. Commonly, the buoy is installed 200 meters depth from the free surface to avoid the wave forces. Therefore, the main forces acting in this part of the system is due to the current flow. In this case, the VIM force is one of the forces that induce oscillations in the buoy, which can cause significantly fatigue damage to the riser system. In this scenario, understand the VIM response of the buoys is important for the system design. In this work, the semi-empirical approach presented by Tsukada et al. (2014), Numerical Simulation of VIM Response of a Submersible Buoy Using a Semi-Empirical Approach, OMAE2014–24187, is applied to perform a parametric study varying the riser length and the properties and dimensions of the buoy of a FSHR system. The main objective of this study is to show the trends of the response due to the variation of this parameters, which assists in understanding the real riser system response presented later in this paper. The real riser system properties and dimensions are obtained from the technical literature and used in the simulations. The results of amplitude and frequency of oscillation of the buoy are compatible with the results of FSHR model test experiments.
An Experimental Investigation About Fatigue Crack Growth Rate of Aluminum Alloy Considering Various Mean Stress
Authors: Choi Yoo , Kim Deok-Geun , Park Jeong-Yeol , Lee Kyoung-Seok , Lee Jae-Myung , Kim Myung-Hyun
Published: October 2015

In general, aluminum alloy is a commonly used for liquefied natural gas (LNG) storage systems. In this regard, it is important to know exact mechanical properties at cryogenic temperature. There are many researches to assess mechanical properties of aluminum alloy, such as tensile strength, fatigue performance and fracture toughness. Fatigue crack growth rate (FCGR) is important to predict the service life. In particular, mean stress effect can significantly affect the fatigue life. In this regard, this study carried out by a series of FCGR test at five different stress ratios (R=0.1, 0.3, 0.5, 0.7 and 0.85).

The major objective of this paper is to suggest a new model that can consider the mean stress effect on FCGR of aluminum alloy in a unified manner. A mean stress equation is incorporated into Paris’ law. In order to validate the model, FCGR test data of aluminum alloy is compared with Walker’s relationship. Compared to the other existing model, the new model is found to exhibit more accurate result compared to Walker model.
Toward a Fatigue Life Assessment of Steel Pipes Based on X-Ray Diffraction Measurements
Authors: Pinheiro Bianca , Lesage Jacky , Pasqualino Ilson , Benseddiq Noureddine , Bemporad Edoardo
Published: October 2015

The present work aims to evaluate the microstructural mechanisms associated with the initiation of fatigue damage of steels used in the petroleum industry. Microdeformations and residual stresses (macrostresses) are evaluated by X-ray diffraction in real time during alternating bending fatigue tests performed on samples taken from an API 5L X60 grade steel pipe. Samples under two different conditions are considered: as-machined and annealed. Microdeformations and residual stresses are estimated from measurements of the full width at half maximum (FWHM) and displacement of the diffraction peak, respectively. The evolution of microdeformations shows three distinct stages (Stages 1–3). Increasing stress amplitude accentuates variations in FWHM and reduces the duration of each stage. Similar variations are observed for the residual stresses. The results from annealed samples allow the comprehension of the role of the initial structure. Changes in the density and distribution of dislocations are observed by transmission electron microscopy using the technique of focused ion beam. Cyclic uniaxial tests are carried out in order to evaluate the material behavior, in both as-machined and annealed conditions, under cyclic loadings. The cyclic material behavior is correlated to the evolution of microdeformations observed during the fatigue bending tests.
COER Hydrodynamic Modeling Competition: Modeling the Dynamic Response of a Floating Body Using the WEC-Sim and FAST Simulation Tools
Authors: Lawson Michael , Garzon Braulio Barahona , Wendt Fabian , Yu Yi-Hsiang , Michelen Carlos
Published: October 2015

The Center for Ocean Energy Research (COER) at the University of Maynooth in Ireland organized a hydrodynamic modeling competition in conjunction with OMAE2015. Researchers were challenged to predict the dynamic response of a floating rigid-body device that was experimentally tested in a series of wave-tank tests. Specifically, COER set up a blind competition, where the device specifications and test conditions were released, but the experimental results were kept private until all competition participants submitted their numerical simulation results.

The National Renewable Energy Laboratory and Sandia National Laboratories entered the competition and modeled the experimental device using both the WEC-Sim and FAST numerical modeling tools. This paper describes the numerical methods used to model the device and presents the numerical modeling results. The numerical results are also compared to the experimental results provided by COER at the completion of the competition.
Collision Tests on Steel-Plated Structures in Low Temperature
Authors: Park Dae Kyeom , Kim Ki Jong , Lee Jong Hwan , Jung Bo Gyeong , Han Xu , Kim Bong Ju , Seo Jung Kwan , Ha Yeon Chul , Paik Jeom Kee , Matsumoto Toshiyuki , Byeon Su Hwan , Kim Min Soo
Published: October 2015

The aim of the study reported herein was to investigate the effects of low temperatures on the crashworthiness of steel-plated structures. A series of material tensile tests were performed to examine the material behaviors at low temperatures. Then, unstiffened steel-plated structure and stiffened steel-plated structure were collided with a cone-shaped drop object to estimate the crashworthiness of steel-plated structures. The material tensile test specimens and test structures were made of Polar class steel for ships and offshore structures which is a sufficient condition of the IACS requirements concerning Polar Class and Strength of Ships. The tests considered room and low temperatures relevant to an Arctic environment and a cryogenic condition. LS-DYNA nonlinear finite element simulations applying a practical approach of modeling techniques were performed to investigate the structural crashworthiness of the steel-plated structures numerically with results of material tensile tests.
A Fundamental Study on Anchor Performance Evaluation for Marine Accident Prevention
Authors: Masuda Mitsuhiro , Minami Kiyokazu
Published: October 2015

From the viewpoint of prevention of the accident of ships under anchorage, an anchor is a very important device. The anchor with various types and performances has been developed over the centuries. For example, JIS types and AC-14 types are mostly applied to Japanese ships at present. However, marine accidents by dredging anchor are not eliminated even now. There still seems a room for improvement of its performance by changing shapes and forms. There may be a problem also in the experiment method and a valuation method. The purpose of this research is to perform an anchor performance re-evaluation for marine accident prevention. The candidates for an experiment are JIS type, AC-14 type, DA-1 type stockless anchor and Danforth type stock anchors.
Effect of Pile-Soil Interaction on Structural Dynamics of Large MW Scale Offshore Wind Turbines in Shallow-Water Western GOM
Authors: Yin Ling Ling , Lo King Him , Wang Su Su
Published: October 2015

The effect of pile-soil interaction on structural dynamics is investigated for a large offshore wind turbine in the hurricane-prone Western Gulf of Mexico (GOM) shallow water. The offshore wind turbine has a rotor with three 100-meter blades and a mono-tower structure. Loads on the turbine rotor and the support structure subject to a 100-year return hurricane are determined. Several types of soil are considered and modeled with a distributed spring system. The results reveal that pile-soil interaction affects dynamics of the turbine support structure significantly, but not the wind rotor dynamics. Designed with proper pile lengths, natural frequencies of the turbine structure in different soils stay outside dominant frequencies of wave energy spectra in both normal operating and hurricane sea states, but stay between blade passing frequency intervals. Hence potential resonance of the turbine support structure is not of concern. A comprehensive Campbell diagram is constructed for safe operation of the offshore turbine in different soils.
Numerical Study of Thermosyphon Protection for Frost Heave
Authors: Abdalla Basel , Fan Chengye , McKinnon Colin , Gaffard Vincent
Published: October 2015

Thaw subsidence and frost heave are two different hazards to pipelines in arctic regions. The former is due to the thawing of permafrost induced by a warm pipeline, while the latter is resulted from a cold buried pipeline that causes ice lens growth upon freezing in the direction of heat loss. Some pipelines may be operated in a wide temperature range and thus subjected to both types of threats.

Two-phase closed thermosyphons have been employed extensively in Arctic projects to protect the permafrost from thawing. The thermosyphons’ response as a “thermo-diode” is the key to this technology. This paper presents a finite element analysis (FEA) based feasibility study for using thermosyphons with pipelines in arctic regions to reduce the potential for frost heave. There are two major challenges in the numerical simulation. One is the efficient modeling of a thermosyphons which works as a heat pump in winter and stops working in summer. This study proposes an anisotropic conduction model that simplifies the thermal-fluid processes within the thermosyphon without overwhelming computational cost. The other challenge is the frost heave modeling, which was recently achieved based on the framework of the porosity rate function. New developments involved in this paper include the extended application to permafrost and transient temperature boundary conditions.

The outcome of this work proves the value of using thermosyphons with pipelines that transfer both cold product. The method introduced here can also be used to optimize the design of new infrastructure and pipelines in permafrost, as well as to assess how thermosyphons work as a mitigation method in existing projects that are affected by frost heave.
Integrated Production Management by Processes: A Case History at the Marine Region
Authors: Flores-Avila Fernando Sebastián , Riaño-Caraza Juan Manuel , Colina-Alvarez Jesús Antonio
Published: October 2015

As part of its strategic plan 2014–2018 Pemex Exploration and Production (PEP) has decided to modify the organizational structure in order to change from a function based structure to a new one based in process, supported on three fundamental axes: People, Processes and Technology. On this direction, it has been assigned to the Technical Resources Management Vice-presidency the responsibility to implement a strategy that will enable to improve performance into the Assets of the Marine Region. This paper presents the experiences and achievements reached by implementing the strategy of “Integrated Production Management by Processes” which goal is to create and implement a management model that will contribute to the optimization of the Asset performance, integrating through the people, management processes, workflows and information and communication technologies.

The “Integrated Production Management by Processes” model, is based on five elements that work integrated and coordinated way; these are:

• Organizational issues.

• Work methodologies.

• Information management.

• Monitoring key performance indicators (KPI).

• Production costs management

The proposal on this paper is based on developing a business process management methodology for PEMEX, by applying the 5 elements of the model to measure current performance of the production assets in order to find the existing gaps between the current management model and the Integrated Production Management by Processes and implement an action plan to close those gaps. In order to homologate and standardize the measurements in PEMEX’s assets, a Capability Maturity Model was developed according to the ISO 9004-2010 and Mexican Standard NMX-CC-9004-IMNC-2009. The maturity model allows weighting each one of the 5 elements into 5 dimensionless levels. The lowest level 1 means that the asset is in the initial stage and it has the Vision of a Functional Management; on the other hand, the highest level 5 means that asset has implemented the new model and has reached a Sustainable Management. To implement the Integrated Production Management by Processes, assets need to demonstrate that Level 4 has been reached.
Application of Artificial Neural Networks in Assessing the Equilibrium Depth of Local Scour Around Bridge Piers
Authors: Sarshari Ehsan , Mullhaupt Philippe
Published: October 2015

Scour can have the effect of subsidence of the piers in bridges, which can ultimately lead to the total collapse of these systems. Effective bridge design needs appropriate information on the equilibrium depth of local scour. The flow field around bridge piers is complex so that deriving a theoretical model for predicting the exact equilibrium depth of local scour seems to be near impossible. On the other hand, the assessment of empirical models highly depends on local conditions, which is usually too conservative.

In the present study, artificial neural networks are used to estimate the equilibrium depth of the local scour around bridge piers. Assuming such equilibrium depth is a function of five variables, and using experimental data, a neural network model is trained to predict this equilibrium depth. Multilayer neural networks with backpropagation algorithm with different learning rules are investigated and implemented. Different methods of data normalization besides the effect of initial weightings and overtraining phenomenon are addressed. The results show well adoption of the neural network predictions against experimental data in comparison with the estimation of empirical models.
Motion Responses of Floating Structures Near Small Islands
Authors: Yang Peng , Gu Xuekang , Tian Chao , Liu Xiaolong
Published: October 2015

The seabed topography near small islands is usually in rugged state, and the water depth can be changed from tens of meters to a few meters in a short distance. Far field waves advancing towards the shore will experience a complex evolution on the shoal. In this environment, the hydrodynamic responses of a floating structure will be largely affected by the non-uniform wave pattern and changeable seabed, and might be quite different from the general responses of a platform in waves with uniform water depth. In this paper, a coupling hydrodynamic model of floating structures and reef topography was established; the incident wave force, diffraction force, radiation hydrodynamic coefficients, motions of a floating structure were calculated. The model was validated by comparing the predicted results with that of model tests. It is indicated that complex seabed topography has a significant influence on the hydrodynamic responses of the floating structure. Moreover, the motions are increased obviously in certain wave periods, with reference to that in far field waves.
Short Term Distribution of Loads Acting on a Cruise Vessel in Extreme Seas Using a Body Nonlinear Time Domain With Second Order Froude-Krylov Pressure
Authors: Rajendran Suresh , Fonseca Nuno , Guedes Soares C.
Published: October 2015

Short term probability distribution of the vertical bending moment acting on a cruise vessel in extreme seas is calculated using a body nonlinear time domain method based on strip theory. The hydrodynamic forces are calculated for the exact wetted surface area under the incident wave profile. The incident potential satisfies the weakly nonlinear free surface condition based on the Stokes expansion. The disturbance potential satisfies the linear free surface and body boundary conditions. Certain practical engineering techniques are employed for the calculation of the body nonlinear forces. The statistics and the probability of distribution of the numerical vertical bending moment are compared with the experimental results measured in the wave tank.
Investigation of Wave Evolution Near Islands by On-Site Measurements and Numerical Simulations
Authors: Gu Xuekang , Liu Xiaolong , Chen Wenwei , Yang Peng
Published: October 2015

Extreme and long-term wave data near small islands, which are quite different from that of open seas, are crucial for the safety of offshore platforms. An environmental measurement system was deployed around a small reef island, which includes three wave buoys. The concerned environment parameters, such as wave height and period, current and wind speeds etc., have been measured by the system in a long-term plan. Meanwhile, a numerical scheme based on shallow water theory was developed, and the numerical simulations of the wave evolution around the islands were carried out and the results were validated with the measured data. It was revealed that the wave statistics changed significantly on the route of wave propagation. The ratios of wave parameters between near island locations and far field were obtained. Based on the method developed in this study, it is possible to predict the wave conditions at a location close to the shore on the basis of the known far field incident wave, which can be used for the design of near shore structures in the future.
“Bigfoot” DVA Semi-Submersible Model Tests and Comparison With Numerical Predictions
Authors: Liapis Stergios , Li Yile , Lu Haining , Peng Tao
Published: October 2015

The Bigfoot direct vertical access (DVA) semisubmersible is a novel floating drilling and production host that provides an attractive alternative to the spar. This concept utilizes heave plates (big feet) that improve the motion characteristics of a semisubmersible in all mild environments (S.E. Asia, W. Africa and Brazil). Bigfoot offers direct-vertical access (DVA) which is often a project requirement. This floater works in all water depths, in particular ultra-deepwater (5000+ ft) where a tension leg platform (TLP) is not an option, supports top tensioned risers and enables drilling and workover operations. The Bigfoot has several advantages over a spar. These include: 1) Quayside topsides integration. This eliminates offshore topsides integration, a significant issue for all spar projects in terms of cost, safety and schedule. 2) A more open deck layout compared to a spar, 3) No fabrication location restrictions as it can be built by many yards worldwide potentially offering local content to a project.

Model tests were undertaken at the Shanghai Jiao Tong University (SJTU) Offshore Basin to assess the dynamic response of the Bigfoot in waves, swell, wind and current. Five mild (non-Gulf of Mexico) environments were considered. In all cases, the floater motions are an order of magnitude smaller than those of a conventional semisubmersible for similar deck payload thus enabling drilling operations and top-tensioned production risers. In a parallel effort, a COSMOS numerical model of the Bigfoot was developed for coupled motion analysis. The experimental results and the COSMOS numerical predictions are in close agreement. In addition to measuring global motions, two heave plates were instrumented with load cells to measure forces and moments. The force measurements from the model tests are in good agreement with numerical predictions using computational fluid dynamics (CFD).