bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation of Nets With Bending Stiffness Normal to Uniform Currents
Authors: Gansel Lars , Jensen Østen , Endresen Per Christian , Føre Martin
Published: November 2013

The tremendous growth of the fish farming industry in Norway over the past decades was supported by new designs and materials for fish farms, enabling bigger fish cages to be positioned in more exposed sea areas. Today, the nets of most fish cages in Norway are made from nylon. Nylon nets are lightweight, relatively easy to handle and at the low cost end of proposed net materials. However, nylon nets also have some unfortunate characteristics like low abrasion resistance and limited tensile strength. Thus, new net materials are proposed to better prevent escapes, protect fish from predator attacks, improve the stability of fish cages and reduce bio-fouling. Some of these materials are stiff in at least one direction and there still is a lack of knowledge about the behavior of nets with bending stiffness in currents and waves. The aim of this study was to determine how nets with bending stiffness deform in different currents and how the deformation influences the drag on the nets and to compare the results with predictions from a numerical model. Three types of net (PET, copper and steel) were clamped to a solid steel bar on the top side, but were otherwise unrestricted. Reflective markers were mounted on the nets and an optical tracking system was used to determine the position of the markers during the tests, thus allowing the determination of the deformation of the net panels. The forces on the net panels were measured with a multi-axis force/torque sensor system. The nets were subjected to several flow speeds between 0.1 and 0.9 m/s. It is shown that bending stiffness and density of nets affect net deformation, as both parameters impact the balance between drag and gravitational forces on the nets. Net deformation leads to a decrease of the projected net area. As the rate of deformation with current speed varies greatly between different net types, the discrepancy between measured drag and drag values normalized to the projected net area at different current speeds follows different relationships for different nets. A numerical model, FhSim was able to predict net deformation of nets with bending stiffness well and it is shown that FhSim could not only account for the effect of bending stiffness on net deformation, but also that the model captures the structural dynamics of nets with bending stiffness in a current.
Capability Plots of Dynamic Positioning in Ice
Authors: Kerkeni Sofien , Metrikin Ivan , Jochmann Peter
Published: November 2013

Dynamic positioning (DP) capability plots in open water are essential tools both for ship design and operational risk assessment. Currently the capability plots are widely used by the whole ship sector. Furthermore, the calculations and representations of the capability plots have been standardized by the International Marine Contractors Association (IMCA). In a capability plot, the wind, current and wave loads are taken into account and the plots are given in polar coordinates [1]. Recent research and ice basin experiments have demonstrated the feasibility of DP operations in ice-covered waters [2]. However, the design of a similar analysis tool as the capability plot is complicated by both a large range of ice parameters and the lack of understanding of the ship/ice interaction physics at low relative velocities [3]. In this paper, the influence of several ice parameters is studied in order to identify the most important variables for DP in ice. The study comprises both ice basin experiments and numerical simulations. The ice basin test results are extracted from the trials carried out at the large ice tank of Hamburg Ship Model Basin (HSVA) within the scope of the European research and development project DYPIC [2]. The numerical modelling is based on a novel high-fidelity simulation approach which is discussed in the paper. Finally, “ice capability plots” are drawn under certain hypothesis and assumptions.
Design of Steel Lazy Wave Riser for Disconnectable FPSO in the Gulf of Mexico
Authors: Cheng Jingyun , Cao Peimin
Published: November 2013

The disconnectable Floating Production Storage and Offloading system (FPSO) is one of the preferred solutions for the deepwater field in the harsh environment and far away from existing pipeline infrastructures. This paper presents a design of steel lazy wave riser (SLWR) system for an internal turret moored disconnectable FPSO in the Gulf of Mexico. The integrated systems of FPSO, disconnectable buoy, riser, and mooring are discussed while focusing on the design challenges of SLWR system. Due to the complexity of SLWR geometry, a systematic configuration approach is introduced based on buoy payload and riser performance criteria. The study includes the strength and fatigue analysis of production, gas export and water injection risers for the connected, disconnecting, and disconnected conditions. The sensitivity of buoy disconnecting due to vessel offset is also presented. It concludes that SLWR with disconnectable FPSO is a feasible and cost effective solution for deepwater field development in the Gulf of Mexico. The study demonstrates the importance of an integrated design approach, and provides guidance for configuring and design of future disconnectable systems with SLWRs.
New Approach for Assessment of Flexible Risers Interference in Shallow Waters
Authors: Ribeiro Elton J. B. , Labanca Edson L. , Alvim Roberto , Veras Otavio
Published: November 2013

This paper presents a methodology to analyze the risers interference connected to an FPSO, which is using turret moored system in shallow water.

It is not feasible in shallow water to use riser free hanging catenary configurations, since there is not enough length in order to dissipate FPSO dynamic response due to wave action, which can cause riser damage at TDP. Furthermore, FPSO static offset is very large, around 30% of water depth, when it is compared with deep water, around 11–12% of water depth.

In order to become feasible a large number of risers connected to a FPSO using a turret moored system in shallow water are needed to use compliant configurations, such as: lazy wave, pliant wave and Lazy S.

As mentioned above risers compliant configurations are capable to avoid riser damage at TDP, but they present a large lateral motion. Thus, riser interference becomes a critical issue to be overcome.

As the applicable standards and rules are not entirely prescriptive about this issue, the riser analyst usually have to adopt independent criteria, such as load cases, internal fluid density, hydrodynamic coefficient considering or not wake effect and clashing criteria (allowable, partially allowable or not). Therefore, the proposed methodology is very robust and was used at FEED studies for FPSO OSX-2/3, both belong to OGX, which are planning to install them at the ending of 2013 in Campos Basin, offshore Brazil.
Two Degrees of Freedom Vortex-Induced Vibration Responses With Zero Mass and Damping at Low Reynolds Number
Authors: Yu Kintak Raymond , Hay Alexander , Pelletier Dominique , Corbeil-Létourneau Simon , Ghasemi Shahin , Etienne Stéphane
Published: November 2013

Vortex-induced vibration is an important phenomenon for offshore engineering. For applications like the piping in the deep water oil exploration projects, the mass ratios can be of order of one [1]. Hence, there is a practical need to understand the effects of low mass ratio on vortex-induced vibrations to enhance design safety. The main purpose of this study is to numerically explore the two degrees of freedom (transverse and streamwise) responses of vortex-induced vibrations of a cylinder at low Reynolds number for the limiting case of zero mass ratio and zero damping. We aim to characterize the responses. In particular, we focus on determining the maximum amplitude values. It is a continuation from the work of Etienne and Pelletier who studied such behaviors at very low Reynolds number (Re < 50) [2].

We investigate the responses in the following parameter space: Reynolds number (75 ≤ Re ≤ 175), reduced velocity (5.0 ≤ Ur ≤ 11.0) and mass ratio (m* = {0, 0.1, 1}) with a fully coupled fluid-structure interaction numerical model based on the finite element method.

Our results are generally in accordance with those from previous works for the displacement trajectories, force phase diagram, and the trends in frequency response and oscillation amplitude. The maximum transverse amplitude is found to be around 0.9 in the studied parameter space. In particular, with zero mass ratio, the maximum transverse amplitude starts to occur at values of reduced velocity higher than 6.5 for Reynolds number larger than 150. This is in contrast to the results of Etienne and Pelletier [2] who found that the maximum transverse amplitude always occurs at the reduced velocity of 6.5 for Reynolds number less than 50. Furthermore, with zero mass ratio, the maximum transverse amplitude increases when the Reynolds number increases. This behavior differs from what was suggested by Williamson and Govardhan [3] for a cylinder oscillating only in the transverse direction at Reynolds numbers in the range of 85 to 200. They found that the Reynolds number has no influence on the maximum transverse amplitude.

We do not notice any response branching in this parameter space. However, the results in the present work clearly consist of two distinct characteristics. This indicates that the investigated mass ratio values encompass the critical mass ratio; whose value is estimated to be around 0.1 to 0.2.
Modeling and Experiments on an Oscillating Water Column Using a Self-Adaptive Air Turbine and Shutter
Authors: Lorenz Patrick , Kimball Richard W. , DiBella Frank , Smith Richard , Ring Scott
Published: November 2013

This paper presents model-scale measurements and numerical models of a floating oscillating water column (OWC) system, consisting of an air cavity coupled with a Wells-type turbine energy extraction device. As waves travel through the OWC, air pressure cycles are generated. The oscillating water column captures the resulting pneumatic energy by directing the chamber pressure and air flow through the Wells turbine. A special feature of the system is a shuttering device that momentarily interrupts turbine air flow. The shuttering device is used to control the cavity pressure for optimum turbine performance. Shuttering in this manner can be shown to improve overall system efficiency up to 20% pressure.

Physical scale models of the OWC system were tested in a wave tank at Maine Maritime Academy (MMA) at 1/30th scale as well as elastomeric diaphragm testing at 1/15th scale, under various conditions. Data from these tests, including cavity pressure response, turbine flow rate, and computed fluid power are discussed. In addition, numerical models of the system were developed using a parametric spring-mass-dashpot methodology and as well as a potential flow model derived for cavity geometry in a global wave field (see section 3).

This paper describes the OWC system with adaptive shutter; comparison of experimental measurements to numerical model predictions; numerical model implementation and measurements of energy absorption/resonant effects within the chamber; and a potential flow derivation.
An Oil Field Structural Integrity Assessment for Re-Qualification and Life Extension
Authors: Nezamian Abe , Altmann Joshua
Published: November 2013

The ageing of offshore infrastructure presents a constant and growing challenge for operators. Ageing is characterised by deterioration, change in operational conditions or accidental damages which, in the severe operational environment offshore, can be significant with serious consequences for installation integrity if not managed adequately and efficiently. An oil field consisting of twelve well head platforms, a living quarter platform (XQ), a flare platform (XFP) and a processing platform (XPA) are the focus of this paper, providing an overview of the integrity assessment process.

In order to ensure technical and operational integrity of these ageing facilities, the fitness for service of these offshore structures needs to be maintained. Assessments of the structural integrity of thirteen identified platforms under existing conditions were undertaken as these platforms are either nearing the end of their design life or have exceeded more than 50% of their design life.

Information on history, characteristic data, condition data and inspection results were collected to assess the current state and to predict the future state of the facility for possible life extension. The information included but was not limited to as built data, brown fields modifications, additional risers and clamp-on conductors and incorporation of subsea and topside inspection findings.

In-service integrity assessments, pushover analyses, corrosion control and cathodic protection assessments and weight control reports were completed to evaluate the integrity of these facilities for requalification to 2019 and life extension to 2030. The analytical models and calculations were updated based on the most recent inspection results and weight control reports. A requalification and life extension report was prepared for each platform to outline the performance criteria acceptance to achieve requalification until 2019 and life extension until 2030.

This paper documents the methodology to assess the platform structural integrity in order to evaluate platform integrity for the remaining and extended design life. An overview of various aspects of ageing related to these offshore facilities, representing risk to the integrity, the required procedures and re assessment criteria for deciding on life extension of these facilities is presented.

This paper also provides an overall view of the structural requirements, justifications and calibrations of the original design for the life extension to maintain the safety level by means of maintenance and inspection programs balancing the ageing mechanisms and improving the reliability of assessment results.
Using Model Test Data to Assess VIV Factor of Safety for SCR and TTR in GOM
Authors: Fontaine E. R. , Rosen J. , Marcollo H. , Vandiver J. K. , Triantafyllou M. , Resvanis T. L. , Larsen C. M. , Tognarelli M. A. , Oakley O. H. , Constantinides Y. , Johnstone D. R.
Published: November 2013

This paper presents results obtained as part of the DeepStar Phase 10 program on VIV Factors of Safety. The objective was to develop a general methodology to calibrate Factors of Safety for VIV-induced fatigue and to apply it to partially straked risers. This was achieved using reliability methods, accepted industry VIV prediction software and state-of-the-art model test experiments.

Most oil companies use a Factor of Safety of 20 when predicting VIV damage using VIV software tools. There are numerous software tools currently in use in industry to predict VIV damage to straked risers and each of them will have different accuracy, and therefore an intrinsic level of conservatism. Understanding the level of conservatism in different VIV prediction software is therefore critical to determining what Factor of Safety to use.

This study benchmarks the latest generation of industry accepted VIV design tools at the time of the study (2011): SHEAR7v4.6, VIVAv6.5 and VIVANAv3.7.24 against high quality VIV data from three separate straked riser experiments. A bias distribution (predicted to measured VIV damage results) is obtained for each software tool as a function of the strake coverage.

A novel reliability framework approach is then developed to incorporate all uncertainties associated with VIV fatigue prediction into a limit state function, including variability in met-ocean conditions and variability in the fatigue resistance of the material characterized by a design S-N curve. The limit state function is analyzed using First Order Reliability Methods to develop Factors of Safety for target probabilities of failure.

The general method is then applied on two case studies involving an SCR and TTR in Gulf of Mexico loop currents, but it can be easily extended to different locations and riser configurations. The resulting FoS range from about 1 to 15 for most software, and are lower than industry standards for VIV prediction. The FoS do not vary markedly for different riser configurations, indicating the possibility of reducing excess conservatism when predicting VIV damage on straked risers.
Subsea Jumpers Vibration Assessment
Authors: Deka Dhyan , Cerkovnik Mark , Panicker Nikhil , Achanta Vamsee
Published: November 2013

Subsea rigid jumpers which are used to connect flowlines and risers to other subsea structures are inherently susceptible to vibration because they must be flexible enough to accommodate translation of the flowline, installation tolerances and settlement of pipeline end terminations (PLETs.) In locations where there are bottom currents, the jumpers can be subjected to vortex induced vibrations. When internal flow rates are high, they are susceptible to flow induced vibration, and they may also be excited by slugging. In some cases, the design constraints force the designs to be 3 dimensional and employ strategies to enhance damping.

This paper describes a methodology for assessing subsea jumpers for vibration induced fatigue. The method employs a combination of transient dynamic, harmonic and modal finite element analysis with the VIV tool SHEAR7. The methodology is able to show generally improved VIV fatigue lives compared to more traditional methods based on DNV-RP-F105 because of the ability to define current loading over the jumper length and to assess the effects of strakes and coulomb damping. Further, the methodology is also capable of assessing the effect of tuned vibration dampers which are sometimes used to suppress FIV.
Determining Fitness for Service of SCRs and Flowlines With Probabilistic Tools
Authors: Cerkovnik Mark , Saldana David , Yang Tracy
Published: November 2013

Inspection of deepwater risers for flaws or pits using ILI tools can be challenging. Some lines are designed as “non-piggable”, and it is not unusual for an inspection to be incomplete because of physical constraints. As with any measurement, there will be a degree of error. While deterministic conclusions cannot be reached based on such incomplete data sets, probabilistic methods can be used effectively to make judgments about fitness for service.

Commonly, different sections along a riser or flowline experience different fatigue spectra and extreme loads. Applying the loads from the sections with the highest loading to all flaws/pits can be too conservative. It is useful to employ statistical methods to assess the probability that a large defect occurs in a region with critical loads. These methods are especially useful when ILI data are incomplete or when estimates of damage must be made based on lines in similar corrosion environments.

Properties and parameters other than inspection findings have an element of uncertainty. Fracture toughness, yield stress, and fatigue crack growth rates will be known in terms of mean and standard deviation. Soil properties may be known in terms of upper and lower bound. Likewise, there will be a range of uncertainty about service history and chemical environment. In such cases where fitness for service is based on the interaction of multiple random variables, Monte Carlo methods are appropriate for determining if the probability of failure is sufficiently low to tolerate. In the case of deepwater risers and flowlines where failure could result in loss of containment of hydrocarbons, permissible failure rates are on the order of 1E−5 to 1E−6 per year.

This paper examines a riser and a flowline case study. For each case, a fitness for service analysis is conducted using a Monte Carlo simulation to evaluate the probability of failure based on incomplete ILI data and statistical characterization of other pertinent parameters. The results are compared against the conclusions of deterministic analysis.
Risk and Reliability Centered Maintenance for Maritime Operations in the Arctic: Experience From Fishing
Authors: McGuinness Edgar , Dypvik Tora Gjermstad , Utne Ingrid Bouwer , Holmen Ingunn Marie
Published: November 2013

The Arctic is a vast area with many future economic possibilities for the oil and gas, shipping and the fishing industries. The climate is harsh, the environment vulnerable, but the potential profits from future expansion in the area are huge. The on-going public debate on the Arctic includes discussions both for and against industrial development in these areas, however the reality is that as resources become scarcer in other parts of the world, Arctic expansion will become inevitable. Therefore adequate preplanning of the activities, understanding of the operational environment and development of barriers against undesired events becomes infinitely more important for sustainable, reliable and safe operation in the future.

The fishing fleet has been operating in the Arctic region for decades and while the safety for the fishers is questionable, it is a matter of resources that drove and will continue to drive this expansion. The IMO’s Polar Code for shipping is now under construction and the fishing fleet will have to comply with this and other regulations for future operations in the Arctic.

This paper focuses on the maintenance and safety management regimes and requirements of the fishing fleet currently operating in the Arctic. With long distances to service and help, and a short operating season, a reliable system is a mandatory requirement for the economic stability of these operations. Mutual benefits may be gained if operational experiences from fishing can be utilized by the oil and gas industry and ship transport when moving their operations into the arctic areas, whereas the fishing fleet can improve their safety performance through closer alignment with those standardized procedures applied in other industries.
PIV Measurements of Flow-Field Downstream of a Cylinder in Uniform Flow and Comparisons With CFD
Authors: Stetson Peter B. , Kinnas Spyros A.
Published: November 2013

This paper examines the ability of two-dimensional CFD models to predict flow downstream of a cylinder in uniform flow. PIV measurements of the flow-field downstream of the cylinder in uniform flow are first presented. “Slices” of the flow at several locations along the cylinder are compared to show the variation of the flow in the cross-stream direction. Then the PIV flow is compared with RANS and LES simulations of the flow. Hydrodynamic coefficients and velocities are compared. In a general sense, two-dimensional CFD can give a functional approximation of the unsteady flow field downstream of the cylinder.
A Fundamental Study on Tsunami Damage Control of Moored Vessels Using the MPS Method
Authors: Masuda Mitsuhiro , Minami Kiyokazu , Masuda Koichi , Ikoma Tomoki
Published: November 2013

When the tsunami attacks in harbors, the vessels moored at the wharf may be unable to be evacuated. In such a case, damages such as, breaking the mooring tethers, grounding on a wharf, drift to land areas and the collision with buildings are assumed. This present paper describes the tsunami simulation and the motion analysis of vessel moored at the wharf using the MPS Method. In this research, the 3D-MPS method is applied. The chart of mooring tethers break was created. The wave height of tsunami and the relation of the break of the mooring tethers were shown by the chart of mooring tethers break. The chart was created about the influence of number of mooring tethers, diameter of mooring tethers and mooring system to the break of mooring tethers.
Coordinators Overview and Lessons Learned From the Galway Bay Seatrials of the FP7 EU Funded CORES Wave Energy Project
Authors: Alcorn Raymond , Lewis Anthony , Healy Mark
Published: November 2013

The paper discusses the lessons learned from the European Funded Framework 7 Research project Components for Ocean Renewable Energy Systems (CORES) which developed and trialed new components and systems for ocean energy devices. The authors are the coordinator and project manager so the paper will give this overview of the project. This will include detail of the work packages, major achievements, significant impacts, summary results and outcomes of the sea trials.
Drilling Riser Design and Analysis for Deepwater Applications
Authors: Cheng Yongming , Qi Tao
Published: November 2013

A riser is a fluid conduit from subsea equipment to surface floating production systems such as spars, TLPs, and semi-submersibles. It is a key component in a drilling and producing system. Drilling risers include the applications in marine drilling (low pressure) and tie-back drilling (high pressure). This paper discusses drilling riser design and analysis for a deepwater application.

This paper first discusses the configuration of marine drilling and tie-back drilling risers. It then presents the drilling riser design procedure and analysis methodology. The riser design and analysis cover the riser tensioner setting, marine operation window, strength and fatigue, etc. A marine drilling riser example is used in the paper to demonstrate the design and analysis for a deepwater application. This paper shows the dynamic strength analysis results for the riser. It then identifies governing locations for the riser design. A tie-back drilling riser example is also provided to illustrate its global dynamic performance. This paper finally discusses the design and analysis challenges of a drilling riser for a deepwater application.
Investigations Into Motion Characteristics of a Multi-Column Type FOWT in Waves and Winds
Authors: Murai Motohiko , Takei Miki , Saeki Hotsuma , Nihei Yasunori , Iijima Kazuhiro , Ikoma Tomoki
Published: November 2013

Many researches about various type of FOWT have been already carried out by many researchers including the authors of this paper. As a result, we know that each type has own advantages and own disadvantages. On the other hand, in general, because the floating type is different for each project, it has not compared its performance among those projects in the same condition. Therefore, the authors have examined the performance of the various types of FOWT under the same experimental conditions.

In this paper, the performance of the FOWT focusing on Semi-submersible type of multi-column type in particular is reported. First, we examined as design requirements the shape of a column with footing, the distance between the columns and the number and the arrangement of the multi-column. Within it, we investigated the combination of the variables for good performance in waves and winds. We manufactured a 1/100 experiment model which is based on the design requirements and carried out the experiment in waves and winds. Then we discuss the effectiveness of the model using the experimental results and the numerical results.
Optimal Plan for Inspection and Maintenance of Structural Components by Corrosion
Authors: Ortega-Estrada Cesar , Trejo Roobed , De Leon David , Campos Dante
Published: November 2013

This paper studies the optimal plan for inspection and maintenance of steel structural components in tension by uniform corrosion, considering the following: A deteriorating model uncertain in time is considered, the probability to detect damage during the inspections is modeled, if damage is detected, the structural component is repaired, the failure probability of the component over time is considered supposing that the demands and capacities are random in time, the optimal plan will be the one in which the expected costs (costs of inspection, repair and failure) are minimum in the life cycle of the component, allowing to detect the number of inspections that minimize the expected costs; to determine the optimal plan, all the possibilities that are given of the tree diagram are studied, where each inspection has two existent possibilities: repair or not to repair, the occurrence possibility of each branch in the resulting tree diagram is calculated. In addition, the influence of the variables and parameters are calculated as: the net discount rate of money (r), uniform corrosion rate (ν), the mean load (μS), failure costs (Cf), repair cost (Crep) inspection cost (Cins) and quality of a nondestructive inspection (η0.5). The results indicate that the optimal number of inspections in the life-cycle of the component is sensible to each of the parameters involved, therefore every value of the variables that intervene in an optimization study must be fully justified.
Wake-Induced Vibration (WIV) of Two Tandem Pre-Tensioned Flexible Cylinders
Authors: Sanaati Bijan , Kato Naomi
Published: November 2013

It is believed that investigations on flow around pairs of cylinders can provide a better understanding of the interference effects than the cases involving larger numbers of cylinders. Studies that deal with the dynamic responses of multiple flexible cylinders with low mass ratios and high aspect ratios are few because of the complexities in the responses. In this paper, the effects of wake interference on the dynamic responses of two pre-tensioned flexible cylinders in tandem arrangement subjected to uniform cross-flow are investigated. The analysis results of the tandem cylinders are presented and compared with an isolated flexible cylinder. Two flexible cylinders of the same size, properties, and pretensions were tested at four different centre-to-centre separation distances, namely, 2.75, 5.5, 8.25 and 11 diameters. Reynolds number range is from 1400 to 20000 (subcritical regime). The aspect ratio of the cylinders is 162 (length over diameter). Mass ratio (cylinders mass over displaced water) is 1.17. The amplitude ratio of the CF vibration of the downstream cylinder, IL deflections of both cylinders, frequency responses in both CF and inline (IL) directions were analyzed. For all the examined separation distances, the downstream cylinder does not show build-up of upper branch (within the lock-in region of the classical VIV of the isolated cylinder). The initial distance between the tandem cylinders cannot remain constant. The distance decreases with reduced velocity because of the unequal IL deflection of tandem cylinders. From the CF frequency response of the lift (transverse) force of downstream cylinder, the highest vibration amplitude at all the separation distances occurs whenever their frequencies transitioned into second modal value. The frequency responses of the upstream cylinder cannot be greatly affected by the downstream cylinder even for small separations in contrast to the downstream cylinder.
Non Linearity of Extreme Vertical Bending Moment: Discussion on the Existing Rule Formulation
Authors: Derbanne Quentin , de Hauteclocque Guillaume , Mienahou Therard
Published: November 2013

The current rule formulation for Vertical Bending Moment is a common formula for all the IACS members. This formula introduces an asymmetry between hogging and sagging bending moment, with a non linear coefficient only depending on the block coefficient. This non linear coefficient is equal to 1.0 for hogging moment (no non linear effect) and is comprised between 1.0 and 1.26 for sagging moment (a maximum of 26% increase for low Cb ships).

Non linear bending moment can be evaluated by non linear seakeeping computations taking into account Froude-Krylov and hydrostatic pressure correction. Extreme bending moment corresponding to a 25 years return period requires very long simulations on a large number of sea states. However some techniques have been developed to shorten the duration of the simulation by defining an equivalent design sea state. It is hence possible to compute in a reasonable time the non linear hogging and sagging moment corresponding to a 25 years return period, and to compare with the rule formulation.

Non linear hogging and sagging coefficients have been computed for a large database of ships, including 19 tankers, 29 bulk carriers, and 9 container-ships, in full load or ballast condition. Results are highly dependent on the ship shape, and are ranging from 0.5 to 1.1 for the hogging moment and from 1.0 to 2.0 for the sagging moment. The difference with the actual rule formulation is shown, and some new formulations are proposed based on ships main particulars, in order to have a better fit with the computation results.
Characterization of the Uncertainties in the Inspection Results of Ultrasonic Intelligent Pigs
Authors: Salama Mamdouh M. , Nestleroth Bruce J. , Maes Marc A. , Dash Chris
Published: November 2013

In-Line Inspections using magnetic flux leakage (MFL) and the Ultrasonic (UT) intelligent pigs are the most common tools used to assess the integrity of pipelines. But, both MFL and UT inspection results are subject to various sources of uncertainties which must be quantified and accounted for in the integrity assessment of the inspected pipeline. A series of pull-through tests (PTT) of seven MFL tools and two UT tools from five service providers was performed on a 12-inch diameter pipe containing pre-existing internal corrosion defects of various length, width, and depth, and located in a variety of circumferential and longitudinal positions. The results of these tests are used to quantify the detectability statistics and the sizing uncertainties of the different tools for future use in developing calibrated probabilistic models for reliability based inspection, quantitative risk assessment and life extension studies for pipelines. The results of the MFL tools were presented in 2012 OMAE conference and this paper presents the results of the two UT tools.
Maximizing Drilling Riser Installation Operability for TLP Top Tensioned Risers
Authors: Campbell Mike , Kaculi Jim , Koska Ryan , Mills Darren
Published: November 2013

Top tensioned risers (TTRs) are a key component in Dry Tree Tension Leg Platform (TLP) systems. TTRs are used for both production and drilling operations.

The operability of the drilling riser system can be a key factor in the project economics. In addition to the in-place operability, maximizing the weather windows for running and retrieval of the drilling riser system minimizes down time and increases operational flexibility.

This paper presents the approach taken to determine drilling riser installation envelopes. It discusses the solutions evaluated for increasing drilling riser installation envelopes and documents the associated equipment selection and specification.
A CFD Simulation of Near Wall Turbulent Flow in Concentric Annulus
Authors: Rahman Aziz , Rodriguez Corredor Fabio Ernesto , Bizhani Majid , Kuru Ergun
Published: November 2013

A CFD simulation study was conducted to analyse the near wall turbulence characteristics of water flow through concentric annulus. The continuity and momentum equations were solved by using a commercial CFD package (CFX 14) with the Shear-Stress-Transport (SST) model option. The simulation results were compared to the experimental data obtained by using high resolution Particle Image Velocimetry (PIV) analyses of water flow in a horizontal concentric annulus. A fully developed turbulent flow of water through a horizontal flow loop (ID = 9.5 cm) with concentric annular geometry (inner to outer pipe radius ratio = 0.4) was used for comparison purpose. Reynolds number ranged from 17,500 to 68,500.

Annular velocity profile obtained from simulation study showed good agreement with the experimental data. Near wall velocity profile obtained from CFD simulation followed the universal wall law (u+ = y+) up to y+ = 11. CFD analyses using the SST model resulted a good number of velocity data up to y+ = 11, which is normally a very difficult task to achieve experimentally.

The CFD analyses using SST model is computationally inexpensive and therefore, can be conveniently used for investigating the near wall turbulent characteristics of flow in concentric annulus.
Numerical Simulation Method for Damaged Ships Under Flooding Condition
Authors: Hashimoto Hirotada , Kawamura Kouki , Sueyoshi Makoto
Published: November 2013

Securing the survivability under flooding condition is one of the most important subjects in ship design. For realizing advanced assessment of damage stability, a numerical simulation method for damaged ships is developed by combining the moving particle semi-implicit method (MPS method) and the ordinary strip method based on potential flow theory. In this method, the flow field around the damaged hull including damaged compartments is solved by the MPS method and that around the intact hull is done by the strip method, separately. In order to validate the proposed method, model experiments are conducted for a damaged pure car and truck carrier in calm water and regular beam waves. Then numerical results of the ship motion and the flooding into the damaged compartment are compared with them. As a result, it is demonstrated that the proposed method has good potential for the prediction of dynamic behaviours of damaged ships under flooding condition.
The Characteristic of Hydrate Exploitation by Depressurization
Authors: Pang Weixin , Li Qingping , Yu Xichong , Sun Fujie , Li Gang
Published: November 2013

According to the schematic and properties of a methane hydrate deposit in Shenhu Area of South China Sea in China, the characteristic of hydrate dissociation, water and gas production were simulated with a depressurization method. The effect of hydrate saturation, porosity and permeability et al. on hydrate dissociation was studied, the key controlling factor and difficulty of gas production from hydrate reservoir by depressurization was confirmed.
Tank Model Testing on the Fish Cage Installed in Variable Depths in Current and Waves
Authors: Kitazawa Daisuke , Shimizu Hiroki , Mizukami Yoichi
Published: November 2013

A fish cage should be submerged to reduce hydrodynamic forces from high waves if the fish cage is installed in an exposed sea area. Usually, the submergible fish cage is suspended from the framework at a fixed depth. The framework is set by floats and anchors at the middle position between water surface and the top surface of the submergible fish cage. The submergible fish cage will be used not only for reduction of hydrodynamic forces but for the other purposes such as choosing the best environment for cultured fishes in the vertical direction, and escaping from the flood with high-level nitrogen or turbidity, harmful algal blooming, and floating ices. In such cases, it is useful for the fish cage to be installed in variable depths. The purpose of the present study is to examine the safety of the fish cage installed in variable depths in current and waves by means of tank model testing. The mooring system consists of a fish cage and four floats. The vertical position of the fish cage is variable by adjusting the buoyancy of these floats. First, the drag of the fish cage was examined by towing test, and the results were compared with the drag estimated by the existing studies. The effects of interaction among twines, the angle of attack, wake, and the top and bottom nets were discussed. Then the fish cage was moored in the water tank, which has the length of 50 m and the width of 10 m. The tank model has a scale of 1/100 of the full-scale model of the fish cage used for tuna farming. The model was made according to Tauti’s similarity law. The water depth was set at 0.68 m by adjusting the position of the variable floor. The motion of the fish cage and four floats, and the tension of the mooring lines between the fish cage, floats, and anchors were measured by the underwater video camera and load cells, respectively. As a result, the drag of the fish cage could be estimated from the experimental results of the drag of a plane net since the results include the effect of interaction among twines. The effects of the angle of attack and the reduction in water current velocity inside the cage were also taken into account. The drag of the fish cage could be estimated well by the above method, while it was underestimated by 10% in comparison with the experimental data. In the water tank testing of the mooring system, the tension of the mooring line increased rapidly with the increase in water current velocity since the drag of the fish cage was proportional to the 1.8th power of water current velocity and increased due to the inclination of the fish cage. The increase in the tension due to wave-induced forces to the fish cage could be negligible when the fish cage was submerged. The safety and the design guideline of the mooring system should be assessed by the simulations using a numerical model, which is being developed by the authors. The experimental data obtained in the present study will be useful for the validation of the numerical model.
Design, Modelling and Analysis of a Combined Semi-Submersible Floating Wind Turbine and Wave Energy Point-Absorber
Authors: Touzón González Imanol , Ricci Pierpaolo , Sánchez Lara Miren Josune , Pérez Morán Germán , Boscolo Papo Francesco
Published: November 2013

Floating platforms for offshore wind tend to be very expensive and different solutions have been proposed to increase their cost-effectiveness. One of them involves the combination of offshore wind generation with other forms of ocean renewable energy, as is the subject of the FP7 project Marina Platform. In particular, wave energy from the sea has been investigated since the ’70s and although a few technologies have already reached a pre-commercial stage, their actual economic feasibility can still be questioned so that the possibility of sharing cables, moorings and even the structure with offshore wind turbine is very interesting also from the point of view of wave energy developers.

This paper presents the design, modeling and analysis of a combined concept composed of a semi-submersible platform hosting a single 5 MW wind turbine and a heaving point-absorber consisting of a floating cylinder placed at the geometric center of the platform.

A preliminary design of the concept is carried out by a frequency-domain analysis focused on the definition of the most suitable geometry with the objective of a limited dynamic response of the platform and satisfactory wave power absorption at the same time. It is shown how the requirement of maintaining reduced amplitude on the platform motions imposes the adoption of relatively slender cylinders as point-absorbers.

After a conventional catenary mooring arrangement is assumed and its basic line parameters determined by applying a quasi-static approach, a global coupled time-domain model is built based on the Cummins equation and the use of panel codes (e.g. WAMIT, AQWA) for the computation of the hydrodynamic coefficients. Moorings are modeled as individual catenary lines whereas the dynamics of the wind turbine are modeled by introducing thrust and power curves as function of the motions of the platform, after previous determination with the Blade Element Momentum theory.

The analysis is carried out over a set of operational sea states for different locations around Europe. Through the analysis of power performance, platform and point-absorber motions and mooring tensions, it is shown how the introduction of a Wave Energy Converter (WEC) can occasionally have a positive effect on the whole response of the platform though the significance of its energy contribution is relatively small and additional synergies have to be sought to justify its adoption.
Three Dimensional Grillage Analysis of Reactions on Supports of a Pre-Erection Block
Authors: Kim Sungchan , Ryu Cheolho , Kim Youngho , Han Changbong , Kim Dong Geun
Published: November 2013

There are many PE(Pre-Erection) Blocks in open areas of the shipyard, which are supported by the wooden, concrete, or steel supports. Their position and numbers are decided on a basis of the workers’ experiences. Recently, many shipyards have been making PE blocks with various shape and weight distribution because of the variety of kinds of ships and their building technology. Seriously, they are treating blocks which have not been experienced. In order to evaluate the reliability of all support plans of PE Blocks in such situation, many man hours (MH) are consumed, and the special knowledge and technology about structural analysis are required. We proposed how to conveniently and quickly evaluate the structural safety on PE block supports and developed an application system to implement the evaluation process with three dimensional part models of the PE block and their weight information. The evaluation is based on the simplification to a grillage model of a PE block and its grillage analysis. The load distribution on the grillage model is calculated by two approaches. The first is that the load distribution on the grillage nodes are estimated with the real weight and the center of gravity of each part of a PE block, which can be provided from design databases of the shipyard. The other is that the load distribution is optimally estimated only with the weight and the center of gravity of sub blocks of a PE block. The latter is useful in the case that block information of mother ships can be obtained without the detail design of the PE block. The integrated system has been comprehensively implemented in order to make the grillage model from the three dimensional CAD models of the PE block and their weight information, and to perform the grillage analysis for the reaction forces on the block supports. In the application program, the grillage model can be automatically built from CAD models of PE block. Also the grillage can be modified by inserting, splitting, and deleting a beam element.
Numerical Simulation of an Oscillating Cylinder at High Reynolds Number
Authors: Mandelli Simone , Muggiasca Sara , Malavasi Stefano
Published: November 2013

In this work a numerical investigation of the main flow field characteristics around a free oscillating rigid circular cylinder immersed in a turbulent flow is proposed (Re ≈ 5 · 104). The cylinder is characterized by high value of mass ratio and mass damping (m* = 145; ξ = 0.6 ÷ 1.14 · 10−3; m*ξ = 0.1 ÷ 0.25). The numerical results are compared with experimental data obtained in the wind tunnel under very similar fluid dynamic conditions. There are few works in literature that consider both numerical and experimental results under these conditions. This is probably due to the experimental facilities limitations and the computational difficulties correlated to modeling the flow at high Reynolds number. A numerical URANS model was developed through a CFD commercial code using a k–ω SST turbulence model in a 3D domain with the aim of matching the experimental results in the last years in the Politecnico di Milano Wind Tunnel on a suspended oscillating cylinder.

The numerical setup is characterized by the use of the DFBI-Morphing (Dynamic Fluid Body Interaction) model that allows reproducing the body motion in response to fluid forces treating the cylinder as a mass-damping-spring system by introducing spring and damping forces acting on it.

A preliminary check of this numerical setup was provided by a benchmark case involving a simple case of fixed cylinder at the same Reynolds number, where the movements of the cylinder were disabled. The numerical results of this case have been compared with experimental and numerical results reported in literature in terms of Drag and Lift coefficients and Strouhal number at high Reynolds numbers (Re ≈ 5 · 104). After that benchmark, the full setup has been checked by considering specific fluid dynamic conditions out of the lock in region in which the oscillations of the cylinder are negligible.

Finally two points of the cylinder steady state response curve in the lock in region were investigated. The numerical model gave good results in terms of amplitude response of the cylinder and aerodynamic forces in agreement with experimental results.

The analysis of the numerical reconstruction of the flow field evolution are therefore considered to have more information on the vortex shedding mode especially in the transition region between 2S and 2P mode.