bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study of Parametric Roll on a Fishing Vessel
Authors: Greco Marilena , Lugni Claudio
Published: November 2013

Present research activity examines numerically the occurrence of parametric roll on a fishing vessel interacting with regular head-sea waves. The adopted solver is an efficient 3-D numerical Domain-Decomposition strategy for the seakeeping of a 6-dof vessel without and with small forward speed and possibly subjected to bottom-slamming and water-on-deck events. Here, the vessel has been assumed at rest and the excitation frequency is varied in the first parametric resonance zone and occurrence and features of the instability are examined in terms of nonlinearities of the incident waves and roll natural-to-incident wave frequency ratio. The analysis is performed both fully within the potential-flow theory and examining the effect on the parametric resonance of the viscous correction to the roll damping obtained from free-decay 3D model tests on the same ship. A system of four cables, horizontal in the mean configuration, will be used experimentally to limit the horizontal vessel motions. Here the numerical solver is used to analyze the influence of cable stiffness and of cable configuration on the vessel behavior and to help the design of the physical set up. The vessel has deep draft and high mean freeboard, these aspects work against the occurrence of bottom slamming and water-on-deck events. Without forward speed, no bottom slamming phenomena were observed while limited number of water-on-deck events with small amount of shipped liquid was recorded for the highest-frequency incident waves with largest steepnesses, among those causing parametric roll.
Marine Hydrokinetic Turbine Power-Take-Off Design for Optimal Performance and Low Impact on Cost-of-Energy
Authors: Beam Mike J. , Kline Brian L. , Elbing Brian E. , Straka William , Fontaine Arnold A. , Lawson Michael , Li Ye , Thresher Robert , Previsic Mirko
Published: November 2013

Marine hydrokinetic devices are becoming a popular method for generating marine renewable energy worldwide. These devices generate electricity by converting the kinetic energy of moving water, wave motion or currents, into electrical energy through the use of a Power-Take-Off (PTO) system. Most PTO systems incorporate a mechanical or hydraulic drive train, power generator and electric control/conditioning system to deliver the generated electric power to the grid at the required state. Like wind turbine applications, the PTO system must be designed for high reliability, good efficiency, long service life with reasonable maintenance requirements, low cost and an appropriate mechanical design for anticipated applied steady and unsteady loads. The ultimate goal of a PTO design is high efficiency, low maintenance and cost with a low impact on the device Cost-of-Energy (CoE).
FloVAWT: Progress on the Development of a Coupled Model of Dynamics for Floating Offshore Vertical Axis Wind Turbines
Authors: Collu Maurizio , Borg Michael , Shires Andrew , Brennan Feargal P.
Published: November 2013

In the present article, progress on the development of an aero-hydro-servo-elastic coupled model of dynamics for floating Vertical Axis Wind Turbines (VAWTs) is presented, called FloVAWT (Floating Vertical Axis Wind Turbine). Aerodynamics is based on Paraschivoiu’s Double-Multiple Streamtube (DMST) model [1] [2], relying on blade element momentum (BEM) theory, but also taking into account three-dimensional effects, dynamic stall, and unsteady wind profiles and platform motions. Hydrodynamics is modelled with a time domain seakeeping model [3], based on hydrodynamic coefficients estimated with a frequency analysis potential method. In this first phase of the research program, the system is considered a rigid body. The mooring system is represented through a user defined force-displacement relationship.

Due to the lack of experimental data on offshore floating VAWTs, the model has initially been validated by taking each module separately and comparing it against known experimental data, showing good agreement. The capabilities of the program are illustrated through a case study, giving an insight on the relative importance of aerodynamics loads and gyroscopic effects with respect to hydrodynamic load effects.
Ship Performance Assessment for Arctic Transport Routes
Authors: Erceg Sandro , Ehlers Sören , Ellingsen Ingrid H. , Slagstad Dag , von Bock und Polach Rüdiger , Erikstad Stein Ove
Published: November 2013

The melting ice cap in the Arctic Sea creates greater operational opportunities not only for shipping routes in areas inaccessible in the past due to ice coverage, but also for the existing commercial shipping routes. Therefore, the economic feasibility of higher polar classes (PC5 and PC4) will be discussed for transit operations on the route from Rotterdam to Yamal LNG terminal. Initially, the ice thickness and coverage along the route until 2050 will be identified following recent forecasting trends. This will lead to the permitted round trips per year for the ice class in question. Consequently, a decision towards the choice of ice class must be made. This choice will be accomplished with the help of the ship merit factor (SMF), which considers the potential earnings arising from the increase in operational days for a higher ice class while accounting for the increased expenditure in the ice free season and areas of operation. As a result, a comparative study will be presented for the LNG sea transport operation on the route from Rotterdam to Yamal, which thereby visualizes a decision-support procedure for an arctic transit operation.
Extreme Sea Conditions in Shallow Water: Estimations Based on In-Situ Measurements
Authors: Le Crom Izan , Perignon Yves , Saulnier Jean-Baptiste , Berhault Christian
Published: November 2013

This paper focuses on the assessment of the environmental extreme conditions in term of wind and waves at the SEMREV wave energy test site for application in the design of Marine Renewable Energy (MRE) devices and components. The paper will first present the existing in situ wind and wave measurements. A prediction chain from global to regional scales, and based on a regional wave model calibrated at the SEMREV location, is then described. It enables to build a specific 22 year hindcast dataset for the test site. Long term extrapolation is finally achieved at the SEMREV location using existing methodologies for deep water conditions. Long term extrapolations methods are usually very sensitive to the parameterization and configuration of the prediction chain and we demonstrate in this study that the best overall performances are reached by a POT method at this stage of development in the prediction chain.
Fully Coupled Floating Wind Turbine Simulator Based on Nonlinear Finite Element Method: Part I — Methodology
Authors: Le Cunff Cédric , Heurtier Jean-Michel , Piriou Loïc , Berhault Christian , Perdrizet Timothée , Teixeira David , Ferrer Gilles , Gilloteaux Jean-Christophe
Published: November 2013

In the present paper, a new fully coupled simulator based on DeepLines™ software is described in order to address floating wind turbines dynamic simulation. It allows its user to take into account either separately or together the hydrodynamic and aerodynamic effects on one or several floating wind turbines. This simulator includes a non linear beam finite elements formulation to model the structural components — blades, tower, drivetrain, mooring lines and umbilicals — for both HAWT and VAWT layouts and advanced hydrodynamic capabilities to define all kinds of floating units and complex environmental loadings. The floating supports are defined with complete hydrodynamic databases computed with a seakeeping program. The aerodynamic loads acting on the turbine rotor are dynamically computed by an external aerodynamic library, which first release includes BEM (blade element moment for HAWTs) and SSM (single streamtube method for VAWTs) methods. The integration in time is performed with an implicit Newmark integration scheme.
Fully Coupled Floating Wind Turbine Simulator Based on Nonlinear Finite Element Method: Part II — Validation Results
Authors: Perdrizet Timothée , Gilloteaux Jean-Christophe , Teixeira David , Ferrer Gilles , Piriou Loïc , Cadiou Delphine , Heurtier Jean-Michel , Le Cunff Cédric
Published: November 2013

The present paper describes the validation and the modeling capabilities of a new fully coupled floating wind turbine simulator based on DeepLines™ software. A first validation, based on code comparison with NREL-FAST software, is presented and shows very good correlation on a rigidly founded 5MW wind turbine in various wind conditions despite the different modeling techniques and assumptions of the two softwares. This benchmark, in addition to the extensive validation on various offshore projects, makes us confident on DeepLines capabilities to assess founded and floating wind turbine behaviour in a complex offshore environment. Furthermore, some simulation results on jacket and floating founded wind turbines, defined in the frame of IEA OC4 project, are presented and highlight the versatility of our simulator to perform offshore and floating wind turbine optimal design.
DYPIC - Dynamic Positioning in Ice: Second Phase of Model Testing
Authors: Haase Andrea , Jochmann Peter
Published: November 2013

DYPIC - Dynamic Positioning in Ice is a European research and development project where the main goal is to customize a dynamic positioning (DP) system for model testing in an ice model basin. To achieve this objective numerous ice model tests are performed. Overall they are divided into two main phases — DYPIC Phase I in 2011 and DYPIC Phase II in 2012. The first phase is documented and presented in [1]. This paper addresses the description of the second phase and the presentation of a selection of results. As the main goal of Phase II is to test the DP system developed in Phase I the trials of the second phase are mainly performed in DP mode, while very few tests that serve separate sub goals within the project are performed in the so called fixed mode where the model is towed through the tank. For the DP mode different configurations of the test setup itself are tested. In order to simulate station keeping the vessel travels either in front or behind the main carriage trying to hold its position relatively to the carriage. The relative motion is captured by optical cameras on the carriage and markers on the vessel. In addition real station keeping tests are performed while the model stayed in the middle of the ice basin and different ice field types are pushed along. The ice features tested in DYPIC Phase II include managed ice fields of different kinds and level ice.
The Rain-Flow Estimate of Fatigue Damage of Combined High and Low Frequency Load Effects
Authors: Huang Wenbo
Published: November 2013

The method is developed for calculating the fatigue damage caused by the combined high and low frequency loads, which are both narrowband Gaussian processes. For the combined high and low frequency process taken as a special case of the wide band Gaussian process, the rain-flow counting identifies the typical small and larges cycles. Some kinds of methods were developed for calculating the probabilistic distributions of stress ranges of small and large cycles, which may be very simple but conservative or accurate but complicated. In this paper, based on the rain-flow counting, a simple and accurate method is derived of calculating the damage caused by small and large rain-flow cycles. The method developed is benchmarked against the rain-flow damage estimate and compared with the existing ones. The numerical analyses show that the estimated damage by the method developed is very close to the rain-flow damage estimate.
Variation of Mechanical Properties of Soft Marine Clay With Methane Gas Content
Authors: Castro Raúl Nava , Audibert Jean M. E. , DeGroff Willard , Gan Kuat C. , Ruckman Paul
Published: November 2013

To quantify the effects of methane gas on mechanical properties of soft marine clay, an exhaustive laboratory testing program was developed using zeolite to uniformly disseminate gas bubbles inside the clay matrix. Results from controlled rate-of-strain (CRS) tests indicated that as the gas content increases, there is a reduction in the interpreted preconsolidation pressure, although the rigidity of the clay with more gas increased throughout the test. Minivane test results indicated that the undisturbed shear strength decreases as the amount of methane gas increases, while the residual and remolded strengths remain practically unchanged, i.e., are independent of the gas content. Similarly results from triaxial tests indicated that the undisturbed shear strength is reduced as the gas content increases, but there was no change in the failure mode. Interestingly, the normalized shear strength increased for the clay with gas, when the samples were tested at 100 percent of deformation per hour. It is theorized that the methane gas bubbles interact with both the clay platelets and the pore water, and, to certain point, bear part of the load, thus modifying the distribution of the load in the soil structure; that is to say, there is a partial load transfer from the gas bubbles to the soil structure, as the clay particles confine the methane gas.
Motion Planning and Tracking for Marine Vessels
Authors: de Aquino Limaverde Filho José Oniram , Fortaleza Eugênio Liborio Feitosa
Published: November 2013

Trajectory tracking is an issue of vital practical importance for manoeuvreing of marine vessels and dynamic position system in many offshore oil field operations. In this work, a flatness based approach is proposed on the tracking control design to define open loop trajectories for a simplified model of the underactuated Hovercraft. The flat outputs are given by using the inverse of the controllability matrix, which allows the design of control law to ensure a global stabilization of the trajectory’s tracking error. Numerical simulations are presented to demonstrate the performance of the tracking controller from arbitrary initial conditions and in the presence of external sinusoidal perturbations. The reference trajectory was chosen with respect to the Earth-fixed frame.
Verification Issues Related to CFD Simulations of Flow Around Circular Cylinders
Authors: Escobar Jose , Celik Ismail , Gutierrez-Amador Albio
Published: November 2013

The classical problem of flow around a stationary smooth circular cylinder is used to evaluate Computational Fluid Dynamics (CFD) transient simulations using two approaches; Body Fitted Grid (BFG) and Immersed Boundary Method (IBM). BFG simulations were performed using a commercial CFD code ANSYS-FLUENT and IBM simulations using an in-house CFD code DREAM. Two dimensional simulations were performed at three different Reynolds numbers; 1 × 103, 1 × 105, and 5 × 105. Each of the cases was simulated using a coarse, medium and fine mesh. CFD simulations were evaluated using the following quantities; drag coefficient, lift coefficient, pressure coefficient, separation angle and the Strouhal number of the first harmonic of the lift coefficient. Average, and amplitude of the evaluation quantities are reported for every case.

Simulations showed the grid dependence of the results, e.g. finer meshes captured higher harmonics of the drag coefficient which coarse meshes smeared due the large numerical viscosity. IBM simulations were also affected by the symmetry of the computational grid. Predicted quantities follow previously reported experimental trends fairly well except in the critical flow regime.

Two dimensional calculations using turbulence models were performed for the case of Re = 1 × 105, and Re = 5 × 105. Turbulent results showed the importance of the grid resolution near the cylinder wall in capturing the physics of the problem.

Three dimensional calculations were also performed and results are compared to those obtained from the two dimensional simulations. As may be expected, discretization error estimation methods using three grid calculations are not satisfactory for this highly unsteady flow problem, especially near the critical regime, 1 × 105 < Re < 5 × 105. This paper dwells on various issues related to verification of calculations for such highly unsteady flows.
Development of a New Physical Model for Experimental Assessment of Expandable Casing Technology Effect on Wellbore Cement Integrity
Authors: Kupresan Darko , Heathman James , Tao Tao , Radonjic Mileva
Published: November 2013

The focus of this novel research was to develop a physical model and apply an experimental approach to explore the effect of casing expansion technology on wellbore cement integrity.
Hydro-Elastic Modelling of an Electro-Active Wave Energy Converter
Authors: Babarit Aurélien , Gendron Benjamin , Singh Jitendra , Mélis Cécile , Jean Philippe
Published: November 2013

Since 2009, SBM Offshore has been developing the S3 Wave Energy Converter (S3 WEC). It consists in a long flexible tube made of an Electro-Active Polymer (EAP). Thus, the structural material is also the Power Take Off (PTO).

In order to optimize the S3 WEC, a hydro-elastic numerical model able to predict the device dynamic response has been developed. The inner flow, elastic wall deformations and outer flow are taken into account in the model under the following assumptions: Euler equation is used for the inner flow. The flow is also assumed to be uniform. Elastic deformation of the wall tube is linearized. The outer flow is modeled using linear potential theory. These equations have been combined in order to build the numerical model. First, they are solved in the absence of the outer fluid in order to obtain the modes of response of the device. Secondly, the outer fluid is taken into account and the equation of motion is solved by making use of modal expansion.

Meanwhile, experimental validation tests were conducted in the ocean basin at Ecole Centrale De Nantes. The scale model is 10m long tube made of EAP. The tube deformations were measured using the electro-active polymer. The model was also equipped with sensors in order to measure the inner pressure. Comparisons of the deformation rate between the numerical model and experimental results show good agreement, provided that the wall damping is calibrated.

Eventually, results of a technico-economical parametric study of the dimensions of the device are presented.
Assessment of Capacity of Grouted Connections in Piled Jacket Structures
Authors: Lotsberg Inge , Solland Gunnar
Published: November 2013

The design of the grouted connections in jacket structures has until recently been based on a control of capacity with respect to axial force in the pile while the effect of the bending moment has been neglected, ref. ISO 19902 (2007). In later design of grouted connections it is observed that the moments in the piles can contribute to more than two times larger stress in the pile than that due to axial load only. A significant moment can hardly be transferred from the pile to the sleeve without sliding of the steel against the grout. This sliding is considered to increase with increasing diameter of the pile. Therefore it is difficult to develop design criteria based on small scale testing. The contact pressure between grout and steel will lead to compressive and tensile stresses in the grout. This requires design criteria for compressive stress and tensile stress in the grout.

ISO 19902 do not require fatigue assessment of grouted connections subjected to wave loading. This was based on a review and assessment of jackets present in the Lloyds database at the time the design formulation was developed. It was assessed that fatigue assessment was not required as long as design was performed with respect to the Ultimate Limit State. However, it is now judged that fatigue is important for jackets with significant dynamic load that exceeds the axial and bending moment from permanent loads.

A review of design standards for grouted connections in jacket structures has shown that there is a need for more relevant test data and revisions of these standards such as ISO 19902 in order to assure reliable design with respect to all potential failure modes.
Fatigue Analysis of a Wave Energy Converter Taking Into Account Different Control Strategies
Authors: Zurkinden Andrew S. , Lambertsen Søren Heide , Damkilde Lars , Gao Zhen , Moan Torgeir
Published: November 2013

Point absorber wave energy converters (WEC) are subjected to random wave loads. In addition, the power production of a WEC and the motions are considerably influenced by the applied control mechanism. For small waves, with a wave period close to the natural period of the oscillating system, the power output may be controlled passively by means of a constant damping coefficient. The energy is extracted proportionally to the square of the body’s velocity. If the wave period is away from the natural period, reactive power may be applied in order to enlarge the resonance bandwidth. Recent studies on a point absorber have shown that the stresses at a particular section of the structure depend on the control parameters. The power is increased by choosing a more advanced control mechanism. The consequences are that the stress amplitudes are higher than for the more conservative control case. In this study, the focus is given on the fatigue damage calculation of a structural detail by taking into account the control parameters of the power take-off system. The predicted fatigue damage is calculated based on the spectral approach. Finally the question will be answered which control strategy is more favorable regarding the trade off between the fatigue damage and power production of the wave energy device.
Dynamic Structural Analysis of a Large-Diameter Riser Consisting of Laminated Composite Material With a Hybrid Numerical Scheme
Authors: Jung Dongho , Kim Hyeonju , Tak Moonho , Lee Kyungjae , Park Taehyo
Published: November 2013

A hybrid numerical scheme is developed to analyze the structural dynamic behavior of a large-diameter riser made of a laminated composite material. The global dynamic behavior of the riser, considered as a beam element subjected to a wave and current, is solved with the finite element analysis method in the time domain. The equivalent elastic modulus of a laminated composite riser for the global dynamic analysis is calculated from the stress-strain relation of a laminate structure with a different elastic modulus. For elements in large displacement and stresses estimated from the dynamic analysis, local structural analysis is performed with the finite element analysis method to examine the structural safety of the laminates of the composite riser, which is considered as a hexahedral element. The developed hybrid numerical tool can contribute to structural safety verification of large-diameter risers composed of laminated composites.
Real-Time Network of Weather and Ocean Stations: Public-Private Partnership on In-Situ Measurements in the Gulf of Guinea
Authors: Quiniou-Ramus Valérie , Estival Rémi , Venzac Pascal , Cohuet Jean-Baptiste
Published: November 2013

Monitoring of meteorological or/and oceanographic conditions is done on many Oil & Gas platforms offshore West and Central Africa (from Nigeria to Angola), but it is often only used in real-time and not necessarily archived on a hard-drive, or it is protected by each company’s IT firewalls thus making it difficult to send the information to the “outer world”.

In 2010, TOTAL Oil & Gas Operator launched a project to give remote and public access to this real-time wind, current and also wave or other meteorological / oceanographic (“metocean”) data. The objectives of this initiative were multiple:

• Improve weather and ocean hindcasts and forecasts, which will be beneficial to all Oil & Gas operations in Africa,

• Help feed a database for future O&G developments;

• Enable design checks after ∼1 year of operation;

• Serve as a “black box” in case of an incident which could be due to environment;

• Help feed or validate ocean and oil spill drift forecast in case of emergency;

• Contribute to the international effort of monitoring the oceans in the long term (operational oceanography, climate change, etc.);

• Encourage capacity building in Africa by supporting development and maintenance of technical solutions to reach objectives

In 2013, with the support of the French Meteorological Office Météo-France, the data from half a dozen platforms offshore Nigeria, Congo and Angola will be available on the World Meteorological Organization’s (WMO) Global Telecommunication System (GTS).

This paper will present the type of metocean stations that are part of this network “MODANET”, the IT architecture that was selected to send it out of the Company’s network, the quality control undertaken by Meteo France before sending it to the GTS, and future possible use of the data that are envisaged.
OTEC Cold Water Pipe Global Dynamic Design for Ship-Shaped Vessels
Authors: Xiang Sherry , Cao Peimin , Erwin Richard , Kibbee Steve
Published: November 2013

Ocean Thermal Energy Conversion (OTEC) technology has been considered as a renewable power generation for the tropical oceans where a thermal gradient from subsea to surface are higher than 20°C since 1980. In 2009, the OTEC technical readiness report has identified that semi-submersible, ship-shaped vessel and spar are most feasible to OTEC application. All three are technically mature and well-established floating facilities and have been widely manufactured and operated in offshore industry all over the world. A pilot OTEC development, led by Lockheed Martin (LM) Industry Team, has configured a semi-submersible floating platform. As an alternative design, SBM is developing OTEC designs based on converted ships. Ship shapes provide good access to facilities for practical operation and maintenance activities. Our study focused on demonstrating the feasibility of constructing and installing a 4 meter outer diameter Cold Water Pipe (CWP) based on conventional land-based manufacture of Fiberglass Reinforced Plastics (FRP) followed by installation with SBM marine equipment. Based on insights gained from this exercise, we will continue to develop the installation methods for larger diameter CWPs.

The CWP is a key design challenge for OTEC since it must be strong enough to withstand the forces and motions while being light enough to be installed with available marine equipment. This paper focuses on the cold water pipe global dynamic performance hosted by a converted ship for a 10MW OTEC plantship offshore Hawaii. The offshore Hawaii location was selected for purposes of comparison rather than the existence of any specific prospective projects. The CWP is connected to the vessel via a sealed gimbal device that allows the CWP’s angular motions to be decoupled from the vessel. The fundamental understanding of CWP vibrations is discussed. The CWP global dynamic responses to extreme storms and operational fatigue environments are presented. Vortex Induced Vibration (VIV) and other design issues are discussed. The key global design considerations of CWP for the ship-shaped vessel are identified and summarized.
Development of an On-Board Wave Estimation System Based on the Motions of a Moored FPSO: Preliminary Assessments From a Field Campaign
Authors: Tannuri Eduardo A. , da Silva Bispo Iuri B. , Simos Alexandre N. , Queiroz Filho Asdrubal N. , da Cruz José J. , Carvalho Rafaella C. A.
Published: November 2013

This paper addresses a wave inference system developed for on-site estimation of directional wave spectra from the measurements of the wave-frequency motions of moored vessels. As a preliminary evaluation of the system’s performance, the results obtained in a 9-month field campaign based on an FPSO operating in Brazil’s Campos Basin are compared to hindcast predictions for the same region displayed by NOAA. The estimation method is based on Bayesian inference algorithms, previously validated by means of numerical and small-scale experimental analysis. A 6-dof inertial measurement unit (IMU) is used for monitoring the motions of the platform. The algorithm also requires the Response Amplitude Operators (RAOs), which in turn depend on the loading conditions of the FPSO. Those are defined before each estimation is performed by means of readings of the tanks’ levels. The accuracy of the predictions also depends on the calibration of two parameters (the so-called hyperparameters of the Bayesian method) and those are specified with respect to the mean period of heave motion. The system is able to identify unimodal or bimodal (cross) spectra using a bimodality criterion combined to an iterative algorithm for separating each component of the global spectrum. As a result, besides the global energy matrix, the statistical parameters required for reproducing the measured directional spectra by means of Jonswap and cosine2s models are provided. The system was commissioned and a 9-month validation campaign was executed. It is shown that the estimated parameters show quite reasonable correlation with satellite-based hindcasts from NOAA for sea states with peak periods larger than 8sec.
Numerical Study of the Turbulent Wake of a Towed or Auto-Propelled Axisymmetrical Body in a Stratified Medium Using LES-VMS
Authors: Sainte-Rose B. , Lenhardt X. , Allain O. , Dervieux A.
Published: November 2013

Numerical simulations of close and far wakes behind an axisymmetrical body in a stratified medium are carried out. Towed and auto-propelled regimes are considered. The parameters of the flow are Pr = 7, Re = 10000 based on the diameter of the cylinder and F = 25. Turbulence is modelled with a Large Eddy Simulation - Variational Multi-Scale approach. Realistic results are obtained for the towed case where the so-called three-dimensional (3D), non-equilibrium (NEQ) and quasi two-dimensional (Q2D) regimes are exhibited with very good agreement with the experiments. In addition, the effect of auto-propulsion on the flow dynamics is satisfactorily addressed.
Optimal Metocean Design of Offshore Tower Structures
Authors: Campos D. , Cabrera Miranda J. M. , Martínez Mayorga J. M. , García Tenorio M.
Published: November 2013

A group of tower type offshore structures in 125 m. water depth is studied. The objective is to determine design and assessment parameters for this kind of structures. The increment in the initial cost of a structure in order to reduce the probability of failure 10 times (ΔCi) yields in the optimal probability of failure. A life quality index (LQI) approach allows making a comparison. Safety factors were obtained as function of ΔCi and hydrocarbons production of the platform.
A Comparison Study of Improved SCR Response for HVS Semisubmersible
Authors: Jing Xiaoning , Qian Roger , Cheng Yongming , Lambrakos Kostas , O’Sullivan Jim , Ermon James
Published: November 2013

A new deep draft semisubmersible HVS (Heave and VIM Suppressed) has been developed at Technip as another wet-tree floating platform option, which achieves significantly improved heave motion and Vortex-Induced-Motion (VIM) performance as compared to conventional semisubmersible concepts. This paper presents results from a study that compares the strength and fatigue performance of a gas export (20 inch) SCR that is supported by either the HVS semi or a comparable conventional semi in 4000 ft or 6000 ft of water depth. Both floaters are designed for the central Gulf of Mexico, and have comparable hull principal dimensions and mooring configurations. For the HVS semisubmersible in an extreme sea state (100-yr hurricane), the reduced heave motion significantly improves SCR strength performance at the Touch Down Zone (TDZ) and effectively eliminates the compression load at the sag bend region. The assessment of SCR fatigue responses indicates that most damage near the TDZ results from wave induced motion fatigue and hull VIM fatigue. The suppressed VIM response of the HVS semisubmersible due to the unique blisters attached to the four hull columns significantly enhances the SCR fatigue life near the critical TDZ. The results from this study confirm HVS as a SCR-friendly wet tree host concept for the deep waters in GoM.
Plastic Response and Failure Prediction of Stiffened Plates Punched by a Wedge
Authors: Liu Bin , Villavicencio Richard , Guedes Soares C.
Published: November 2013

Experimental tests have been performed to examine the response of small-scale stiffened plates laterally punched by a wedge. The specimens are supported at two opposite edges and the indenter is located at the mid-span. In the unsupported edges, the ends of the stiffeners are either connected to transverse stiffeners or remain free. The obtained force-displacement responses show a good agreement with the simulations performed by the LS-DYNA finite element solver. The finite element model includes defining the experimental boundary condition so as to simulate small axial displacements of the specimen at the supports. The strain hardening of the material is defined using experimental data of quasi-static tension tests and the critical failure strain is evaluated using tensile test simulations. The results show that the response of the specimens is highly sensitive to the amount of restraint provided at the supports. In addition, simplified calculations are proposed to evaluate the contribution of each structural component on the energy absorbed by the stiffened plate specimens.
Fundamental Research on the Behaviors of Floating Vessels Moored to Floating Piers in Tsunami
Authors: Masuda Koichi , Ikoma Tomoki , Masuda Mitsuhiro , Murata Kazuki
Published: November 2013

Tsunami disasters of floating vessels moored to a quay are complex, such as breaking of the mooring lines and then drifting and collision of floating vessels. There was an example in which a mooring tether of a ship moored to a floating pier did not break in the damage of tsunami. This was confirmed in Shiogama Harbor in Miyagi Prefecture during the East Japan great earthquake which occurred on March 11, 2011. The objectives of this paper are to clarify the effect of reducing mooring tether force in the case of a ship moored to a floating pier, by means of the 3D-MPS method, as well as the advantages of a floating pier for a fixed mooring quay. In addition, in this paper the authors discuss the following items: 1) force of a tsunami wave on the piles of a floating pier; and 2) response characteristics for various incidence angles. Also, we propose measures to prevent drift of a floating pier in tsunami. Finally, these results are used for development of a floating pier for prevention of a vessel being washed away by tsunami.
Evaluating Synergistic Effects of Corrosion in Petroleum Service
Authors: Fischer Michael , Gamino Marcus , Pascali Raresh
Published: November 2013

Corrosion within the petroleum industry is a growing concern due to crude composition and a trend toward higher pressure, higher temperature environments. Relevant to corrosion are the processes through which materials are qualified for corrosive environments. This study evaluates the current status of testing materials for erosion and electrochemical attack and suggests a new method for testing.
Numerical Simulation of Complex Fracture Network Development by Hydraulic Fracturing in Naturally Fractured Ultratight Formations
Authors: Hofmann Hannes , Babadagli Tayfun , Zimmermann Günter
Published: November 2013

The creation of large complex fracture networks by hydraulic fracturing is imperative for enhanced oil recovery from tight sand or shale reservoirs, tight gas extraction, and Hot-Dry-Rock (HDR) geothermal systems to improve the contact area to the rock matrix. Although conventional fracturing treatments may result in bi-wing fractures, there is evidence by microseismic mapping that fracture networks can develop in many unconventional reservoirs, especially when natural fracture systems are present and the differences between the principle stresses are low. However, not much insight is gained about fracture development as well as fluid and proppant transport in naturally fractured tight formations. In order to clarify the relationship between rock and treatment parameters, and resulting fracture properties, numerical simulations were performed using a commercial Discrete Fracture Network (DFN) simulator.

A comprehensive sensitivity analysis is presented to identify typical fracture network patterns resulting from massive water fracturing treatments in different geological conditions. It is shown how the treatment parameters influence the fracture development and what type of fracture patterns may result from different treatment designs. The focus of this study is on complex fracture network development in different natural fracture systems. Additionally, the applicability of the DFN simulator for modeling shale gas stimulation and HDR stimulation is critically discussed.

The approach stated above gives an insight into the relationships between rock properties (specifically matrix properties and characteristics of natural fracture systems) and the properties of developed fracture networks. Various simulated scenarios show typical conditions under which different complex fracture patterns can develop and prescribe efficient treatment designs to generate these fracture systems.

Hydraulic stimulation is essential for the production of oil, gas, or heat from ultratight formations like shales and basement rocks (mainly granite). If natural fracture systems are present, the fracturing process becomes more complex to simulate. Our simulation results reveal valuable information about main parameters influencing fracture network properties, major factors leading to complex fracture network development, and differences between HDR and shale gas/oil shale stimulations.
Tethered Catenary Riser: A New Deepwater Concept
Authors: Legras Jean-Luc , Pillet Baptiste
Published: November 2013

A new riser concept is proposed by Subsea 7 for field development in deep and ultradeep waters: the Tethered Catenary Riser (TCR)-patent pending. The concept consists of a number of steel catenary risers (SCRs) supported by a subsurface buoy which is tethered down to sea-bed by means of a single pipe tendon and anchored by means of a suction pile; flexible jumpers are used to make the connection between the Floating production Unit (FPU) and the buoy. Umbilicals run without interruption from the FPU to their subsea end while being supported by the buoy.

The system has all the advantages of de-coupled riser arrangements: flexible jumpers effectively absorb platform motions, thereby the rigid risers and tendon have very small dynamic excitation. The system can be installed before FPU arrival on site, which improves the time before first oil. Analyses have shown that, with adequate geometry of the buoy, the latter is sufficient stable to induce acceptable tilt and twist when different arrangements of SCRs and flexible jumpers are installed, and under accidental scenarios during the in-place life.

The riser system is best designed for a number of risers between 4 and 8, in addition to a number of umbilicals, thus convenient for one or two drilling centers.

Results of the basic engineering work on the TCR clearly indicate that it is possible to have a robust design using presently qualified materials and technology. The components used in the TCR are all field proven as they are commonly used in existing riser systems.

As a result of installation studies, a method very similar to the one commonly used by Subea7 for Single Hybrid Risers (SHRs) has been selected for the buoy and tether system. Placement of rigid risers, jumpers and umbilicals is as done by Subsea 7 for the Buoy Supporting Risers (BSRs). This method is well adapted for installation by the new Subsea 7 flagship vessel Seven Borealis which is able to perform heavy lift and pipe laying.

The Tether Catenary Riser is a credible option for use in deep water developments all over the world. Since all the components, design methods and installation procedures are fully qualified and familiar to Subsea 7, the concept is cost effective and ready for project application.
Risk Based Inspection for Aged Offshore Pipelines
Authors: Stadie-Frohbös Gundula , Lampe Jörg
Published: November 2013

Today risk based inspection (RBI) has become very popular as it allows the inspection budget to be used more efficiently compared to conventional inspection procedures. The key parts of a risk based inspection programme for aged pipelines is the determination of all relevant risk driving effects for each specific pipeline, the definition of acceptance criteria and the assessment of the residual lifetime for the pipeline. These tasks require a high level of co-operation with the pipeline operator and the RBI-experts.

This paper describes some of the major aspects of the methodology developed to estimate the risk to offshore pipelines. Based on the assessment of the risk an optimised inspection strategy can be developed.

The complete RBI-process typically starts by gathering all relevant data used in design phase (including construction phase) and operation phase. In most cases a variety of risk assessment methods will be used, depending on the quality of existing pipeline data. When insufficient data is available a simple qualitative assessment with an index procedure can be used. With more detailed data available the method becomes a semi-quantitative approach.

This paper presents the results of a general risk assessment of 22 aged offshore pipelines. Although only basic data has been available this was sufficient to work out reliable results within a semi-quantitative approach. Depending on varying wall thickness, diameter, etc. a pipeline was divided into several different segments. The assessment reveals different governing threats and failure modes for pipelines and risers, like ageing, free span or corrosion. In a final step the results of the risk assessment are used for the optimisation of the inspection intervals within the proposed risk based inspection framework.
Long-Term Extreme Response of Marine Structures Considering the Combination of First and Second Order Wave Effects
Authors: Sagrilo Luis Volnei Sudati , de Sousa Fernando Jorge Mendes , Bazán José Antonio Vargas , Gao Zhen , Naess Arvid
Published: November 2013

In this paper, the long-term extreme response of a floating marine structure subjected to first and second order (slow-drift) wave effects is addressed. The proposed formulation is based on the long-term up-crossing rate, which is obtained by integrating the contribution of all short-term sea states. In order to speed up the evaluation of the long-term integral, an analytical expression for the short-term responses up-crossing rates was adopted. This expression is based on Hermite polynomials, and considers the response as a second order Volterra stochastic process. This formulation was applied to evaluate the 1-yr, 10-yr and 100-yr lateral motions of a circular-shaped monocolumn platform, and the non-Gaussian (nonlinear) results are compared with those obtained by assuming the response as a Gaussian process.
CFD Simulation of Flexible Ship in Regular Head Waves
Authors: Hu Changhong , Liao Kangping , Duan Wenyang
Published: November 2013

The ship springing is continuous vibration of the hull girder due to encountered wave excitation, which is considered as a typical fluid-structure interaction (FSI) problem. In this study, a CFD approach is proposed for modeling ship springing induced by large amplitude regular waves. In the CFD model, nonlinear free surface flows are solved by a finite difference method based on CIP (Constraint Interpolation Profile) method. Flexible structure is calculated using one dimensional finite element method by idealizing the ship structure as a beam. A volume weighted method, which is based on IB (Immersed Boundary) method, is applied to couple the FDM and the FEM. The proposed numerical model is validated against an experiment on a flexible barge in regular waves. Discussions are made on the numerical results.
Non Linear Wave Loading of the 3D FE Structural Model of Floating Bodies
Authors: de Lauzon Jérôme , Sireta François-Xavier , Malenica Sime
Published: November 2013

Different numerical methods exist to treat the non-linear wave body interaction problem. These methods go from very complex CFD simulations (VoF, SPH…) to simpler potential flow based methods. Within the potential flow methods, different types of numerical approaches also exist, going from very complex fully nonlinear time domain methods to simpler hybrid frequency-time domain methods. In this paper, only the hybrid frequency-time domain potential flow methods are of concern.

The basic principle of these methods is to use the linear frequency domain data and transfer them to the time domain (Cummings-1962, Ogilvie-1964) using the inverse Fourier transforms. Once in the time domain, all kind of nonlinearities can be added on top of the linear solution. This method showed to be very computationally efficient for global behavior of the floating bodies. However, in the context of the body structural response, it is not trivial to make the load transfer from the 3D hydrodynamic panel model to 3DFE model of the structure. One of the main problems concerns the radiation part of the potential which comes into the play through the well-known convolution integral of the impulse response functions. Within the hydro-structure interaction problem which is of concern here, the straightforward application of the Cummings principles leads to the convolution integral for every pressure point (either on hydrodynamic or structural mesh) which can lead to very expensive numerical simulations.

Previous study by Tuitman, Sireta, Malenica and Bosman (2009) proposed the use of the fast Fourier transform (FFT) to compute the radiated wave loads at each point of the structural model, as a post-processing of the seakeeping calculations.

In this way the CPU time is significantly reduced but the slight unbalancing of the 3DFE model remains. In this paper, we propose the direct use of the local radiated pressure impulse response functions and we show that a good numerical implementation of such method can result in acceptable CPU time with perfect balance of the 3DFE model.
Linear Dynamic Stability Analysis of a Surface Piercing Plate Advancing at High Forward Speed
Authors: Ommani Babak , Faltinsen Odd M.
Published: November 2013

The dynamic stability of a surface-piercing plate advancing with high forward speed in horizontal plane is investigated in the scope of linear theory. The hydrodynamic forces on the plate in sway and yaw are presented in terms of frequency and forward speed dependent added mass and damping coefficients. Flow separation from the trailing edge of the plate is considered. A time domain boundary integral method using linear distribution of Rankine sources and dipoles on the plate, free surface and a vortex sheet is used to calculate these hydrodynamic coefficients numerically. Comparison between the current numerical results and previous numerical and experimental results are presented. Using linear dynamic stability analysis the influence of hydrodynamic coefficients on the plate’s stability is investigated as a simplified alternative to a semi-displacement vessel.
Buckling and Ultimate Strength Assessments of Ship Structures
Authors: Zhang Shengming
Published: November 2013

This paper presents buckling and ultimate strength assessment methods for ship structures. Buckling and collapsing analysis approaches for plates, stiffened panels and hull girders are described and their development history and employments in ship design assessments are reviewed and discussed. Examples using non-linear finite (FE) element analysis are given and comparisons between results obtained by formulae and FE analysis are carried out. Lloyd’s Register’s recent research and development work on ultimate strength and its applications to existing oil tankers and bulk carriers are also presented.