bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation-Based Estimation of Collision Risk During Ship Maneuvering in Two-Lane Canal Using Mathematical Maneuvering Group Model and Automatic Identification System Data
Authors: Asmara I. Putu Sindhu , Kobayashi Eiichi , Artana Ketut Buda , Masroeri Agoes A. , Wakabayashi Nobukazu
Published: September 2014

This paper proposes a simulation-based method to estimate collision risk for a ship operating in a two-lane canal. According to rule 9 of the Colreg-72 navigation rules, in a narrow canal, a vessel shall keep as near to the wall that lies on its starboard side. However, a busy harbor entered through a narrow canal still presents impact hazards. Certain conditions in a two-lane canal, such as a head-on situation in the straight part of the canal during an overtaking maneuver and large curvature of a turning maneuver in the bend part of the canal, could lead to accidents. In the first condition, the ship alters its own course to the port side to overtake another ship in the same lane but the course altered is too large and hits the wall of the canal. In the second condition, the target ship may take an excessively large turn on the bend part of the canal, causing collision with the ship on the opposite lane. Collision risk is represented as the risk of damage to the ship structure and includes the probability of impact accident and severity of structural damage. Predictions of collision probabilities in a two-lane canal have been developed based on a simulation of ship maneuvering using a mathematical maneuvering group (MMG) model and automatic identification system (AIS) data. First, the propeller revolution and rudder angle of the subject ship are simulated to determine safe trajectories in both parts of the canal. Second, impact accidents are simulated for both conditions. The ship’s speed, and current and wind velocity are randomly simulated based on the distribution of the AIS and environment data for the research area. The structural consequences of the impact accident are measured as collision energy losses, based on the external dynamics of ship collision. The research area of the two-lane canal is located at the Madura Strait between the Java and Madura islands in East Java of Indonesia, as shown by the red line in Figure 1. A project for developing a new port and dredging a new two-lane canal to facilitate an increase in the number of ship calls is currently underway in the research area. Figure 1 shows the ships’ trajectories plotted using the AIS data as on January 1, 2011. The trajectories are mostly seen to be coming out of the canal, confirming that it is shallow and needs to be dredged.
A Systematic Approach to Risk Assessment: Focusing on Autonomous Underwater Vehicles and Operations in Arctic Areas
Authors: Utne Ingrid Bouwer , Schjølberg Ingrid
Published: September 2014

Climatic degradation of equipment, in combination with stringent requirements for human safety and minimalistic environmental impact, need to be addressed through improved risk assessment in vulnerable areas, such as the Arctic. The performance of technologies and risk related to its utilization, for example in terms of autonomous operations, significantly impact future requirements for oil and gas exploration and production. An interdisciplinary and systemic approach integrating both risk to the environment and to humans is needed as the challenges related to operation in extreme environments directly impact risk, costs, and the general societal acceptance of the activities. Development of such an approach focusing on autonomous underwater vehicles (AUV) and operations is addressed in this paper.
Wind Induced Nonlinear Response of Coupled Spar Platform
Authors: Jameel Mohammed , Ahmad Suhail , Islam A. B. M. Saiful , Jumaat Mohd Zamin
Published: September 2014

The oil and gas exploration has moved from shallow water to much deeper water far off the continental shelf. Spar platforms under deep water conditions are found to be the most economical and efficient type of offshore platform. Several Spar platforms installed in the Gulf of Mexico and North Sea proves its suitability for deep water exploration. Accurate prediction of motions of a Spar hull is very important for the integrity and associated costs of the riser/mooring line. The most common approach for solving the dynamics of Spar platform is to employ a decoupled quasi-static method, which ignores all or part of the interaction effects between the platform, mooring lines and risers. Coupled analysis, which includes the mooring lines, risers and platform in a single model, is the only way to capture the damping from mooring lines and risers in a consistent manner. The present coupling is capable in matching the forces, displacement, velocities and acceleration for mooring line with Spar hull at the fairlead position and riser with Spar hull at the riser keel connection. It can handle possible significant nonlinearities. The output from such analyses will be platform motions as well as a detailed mooring line and riser responses. In actual field problems hydrodynamic and aerodynamic loads act simultaneously on Spar platform, mooring lines and risers. In finite element model, the entire structure acts as a continuum. This model can handle all nonlinearities, loading and boundary conditions. The selected configuration of Spar platform is analysed under wave force together with wind loading and its structural response behaviour in steady state is studied. An automatic Newmark-β time incremental approach in ABAQUS/AQUA environment has been implemented to conduct the analysis in time domain. The wind force acting on the exposed part of the platform encompasses mean and fluctuating wind components. The frontal region includes the topside assembly and the spar hull portion above the sea level. High degree of nonlinearities makes the solutions convergence sensitive and it requires large number of iterations, at each time station. Spar responses in surge, heave and pitch along with top tension in moorings are computed. The coupled Spar experiences significant lateral shift along wave direction due to wind loading. Increase in standard deviation shows the participation of wind loading giving higher fluctuations. The CML tension increases for wind loading but the extent of the tension fluctuations under wind loading is not much due to high pretension of mooring line.
Improvement of Resistance and Wake Field of an Underwater Vehicle by Optimising the Fin-Body Junction Flow With CFD
Authors: Toxopeus Serge , Kuin Roderik , Kerkvliet Maarten , Hoeijmakers Harry , Nienhuis Bart
Published: September 2014

To control underwater vehicles appendages such as rudders or fins are generally used. These appendages induce added resistance and deteriorate the quality of the inflow to aft control surfaces or propeller, due to the formation of amongst others horseshoe vortices.

In this paper, CFD is used to study the flow around a typical wing-body junction and to obtain insight in how to suppress the horseshoe vortex. For a generic submarine the impact of a range of modifications of the sail on resistance, propulsion and wake field is investigated. Design guidelines regarding the most promising modifications will be given. It will be shown that quite significant improvements of the resistance as well as the wake quality can be obtained by properly designing the junction between the appendage and the hull.
Dynamic Interaction Analysis of a 2D Propulsion Shaft-Ship Hull System Subjected by Sea Wave
Authors: Tian Zhe , Yan Xinping , Li Zhixiong , Zhang Cong
Published: September 2014

Since there is an evident tendency of development of large scale ships, the interaction between the propulsion shaft and ship hull becomes severe due to the tremendously increased ship size. As a result the reliability of the vessels has been put in an important position by the companies and the governments all over the world. The excited forces caused by severe sea waves have considerable effects on the hull deformation which could have further impact on the shaft propulsion system. This paper aims to investigate the coupling dynamics between the large ship propulsion system and hull subjected by sea wave in 2-dimensional circumstance. To look into the coupling mechanism between the ship propulsion shaft, hull and sea waves, a 2-dimensional novel model of large ship propulsion-hull coupling system is presented in this work to analyze the dynamic interactions of the ship propulsion system and hull. According to the dynamic equations of the coupling model, the dynamical responses of the ship shaft and hull are obtained under different stiffness of the support bearings. The analysis indicates that choosing the suitable stiffness of bearings have an important effect on the coupled system.
Gear Contact Fatigue Reliability Analysis for Wind Turbines Under Stochastic Dynamic Conditions Considering Inspection and Repair
Authors: Dong WenBin , Moan Torgeir , Gao Zhen
Published: September 2014

Reliability is one of the most important features of the wind turbine gearbox, especially in offshore wind turbines (OWTs). This paper describes a general way to perform gear contact fatigue reliability analysis for wind turbines considering inspection and repair. A simplified predictive surface pitting model for estimating gear fatigue lives is applied to establish the ‘so-called’ limit stated functions. The National Renewable Energy Laboratory (NREL)’s 750kW land-based wind turbine is used to perform time domain simulations considering different wind speeds that the turbine will experience, whose occurrence frequencies are described by a generalized gamma distribution. The time series of the torques in the main shaft are obtained from the global dynamic response analysis of the wind turbine. The time series of the gear contact forces are obtained from the dynamic analysis of the gearbox through multi-body simulation. The 2-parameter Weibull distribution is used to fit the long-term probability distribution of the gear tooth contact pressures. The reliability analysis is based on fracture mechanics (FM) analysis of crack growth. Finally the sensitivity of the reliability index and failure probability on initial crack size, critical crack size, detectable crack size, crack size after repair, material property and environmental loads is estimated considering the effect of inspection.
Numerical Study on the Residual Ultimate Strength of Hull Girder of a Bulk Carrier After Ship-Ship Collision
Authors: Yamada Yasuhira
Published: September 2014

The purpose of the present study is to investigate residual Ultimate Longitudinal Strength (ULS) of bulk carriers after ship-ship collision. A series of a large-scale explicit finite element analysis (FEA) as well as simplified analysis (SA) are carried out using a cape size bulk carrier. In order to accurately investigate collapse mechanism of “damaged ships” under vertical bending moment nonlinear FEA are carried out where two steps analysis is adopted. First step is ship-ship collision analysis; Second step is ULS analysis of the damaged ship. Ship-ship collision analysis is carried out assuming the right angle collision at the midship region of the struck ship, and damage extent of the struck ship is estimated with varying collision speed of 3kt, 6kt, 9kt and 12kt. In the second step of analysis, residual ULS analysis is carried out taking into account residual stress and deformation of the struck ship caused by ship-ship collision. Collapse mechanism of the bulk carrier in damaged condition due to sagging moment as well as combination of longitudinal and horizontal bending moment is investigated and discussed in detail. ULS of hull girder of the bulk carrier in intact condition is also estimated and compared with that in damaged condition. The effect of damaged condition on the reduction of ULS is discussed in detail. Finally some of numerical methodologies are summarized in assessing residual ULS of hull girder after collision.
Study on Breather-Type Rogue Wave Based on Fourth-Order Nonlinear Schrödinger Equation
Authors: Lu Wenyue , Yang Jianmin , Lv Haining , Li Xin
Published: September 2014

Rogue wave is a kind of wave that possesses concentrated energy, strong nonlinear and enormous devastating. When it interacts with the deep-sea structures, the structure will suffer a serious threat, and it may even cause significant harm to the offshore staff and property. Studies on the mechanism of rogue wave are of great significance to the platform design and security. It is also one of the hot issues on the waves of hydrodynamic studies. Some breather-type solutions of NLS equation have been considered as prototypes of rogue waves in ocean. They can appear from smooth initial condition only with a certain disturb given by the exact solution of NLS. In this paper, we have numerically studied rogue waves based on fourth order nonlinear Schrödinger equation. We show that the peaks of the largest amplitude of the resulting waves can be described in terms of the Peregrine breather-type solution as the solution of NLS equation.
Fatigue Assessment of Thin Welded Joints From Invar Alloy by Local Stress Concept
Authors: Oh Dong Jin , Lee Jae Myung , Kim Myung Hyun
Published: September 2014

The aim of this paper is to investigate the fatigue strength of the Invar alloy weld joints. Invar alloy is commonly used in cryogenic applications where a high degree of dimensional stability is required under temperatures. It is widely used in primary and secondary barriers of membrane-type liquified natural gas (LNG) containment system. The fatigue assessment of Invar alloy weld joints is evaluated based on the nominal stress, structural stress approach and effective notch stress approaches. A series of fatigue tests were carried out for two different types of welded joints with raised edge specimens and overlap joint specimens at room and cryogenic temperatures. The evaluation of the results exhibit that the local stress concept using the reference notch radius of r = 0.05 mm can be applied to the fatigue design of Invar alloy weld joints for plates with thicknesses less than 5 mm. The results are also compared with the available published data. Finite Element Analysis (FEA) is carried out to investigate FAT value and slope of the design curve for Invar alloy weld joints. The suggested fatigue design curves based on the effective notch stress concept indicate a lower FAT value compared to steel weld joints by IIW recommendations.
A Coupled Aero-Hydrodynamic Simulator for Offshore Floating Wind Turbines
Authors: Duan Lei , Kajiwara Hiroyuki
Published: September 2014

Offshore floating wind turbines (OFWTs) are expected as the future of wind energy. However, the analysis of OFWTs is much more complicated than that of fixed-bottom wind turbines. The simulators currently in use, based on the classic blade element momentum (BEM) theory, will be inadequate while used on OFWTs because of the unsteady motions induced by wind and waves. Thus, simulators with advanced approaches are of necessity for analyzing OFWTs. In this work, a coupled aero-hydrodynamic simulator in MATLAB/Simulink is developed, for simulating the response and aerodynamic performance of OFWTs under wind and waves in the time domain. For aerodynamics, the code uses an unsteady BEM model or the free vortex wake method (FVM) to calculate the aerodynamic loads and performance of the wind turbine. For hydrodynamics, a linearized classic marine hydrodynamic model, based on the frequency-dependent parameters obtained from the code of WAMIT, is employed to calculate the hydrodynamic loads of the platform by solving the hydrostatic, diffraction and radiation problems with fluid-memory effect. Furthermore, Morison’s equation and the strip theory are applied to calculate the nonlinear viscous drag for improving the quality of the model. Finally, a series of cases with different wind and wave conditions is tested on a sample model combining “NREL offshore 5-MW baseline wind turbine” with “OC3-Hywind platform”. The results show that the simulator is able to predict the response and aerodynamic performance of OFWTs under wind and waves. Moreover, the FVM is more suitable for analyzing the aerodynamic performance of OFWTs than the unsteady BEM model because of its higher fidelity and less limitations.
A Study on the Impact Load Acting on an FPSO Bow by Steep Waves
Authors: Hong Sam-Kwon , Lew Jae-Moon , Jung Dong-Woo , Kim Hee-Taek , Lee Dong-Yeon , Seo Jong-Soo
Published: September 2014

Among offshore floaters used to develop offshore resources, FPSO and FSO have a storage function whereas semi-submersible, Spar and TLP have only production function. The floaters with the storage function such as FPSO and FSO are designed as the typical ship type concept compared to the other floaters with small water plane area.

In order to design the floaters for offshore resource development, it is needed to estimate the seakeeping performance under operating condition and survival conditions and then carry out the structural design based on seakeeping performance results. The environment conditions of 1yr, 10yrs, 100yrs or 1,000 yrs return periods are used based on the metocean data of the installation field to evaluate the seakeeping performance under operating and survival conditions. In general, the wave conditions with the maximum wave heights for each return periods are selected on each wave contour lines in the wave scatter diagram. Then the seakeeping performance is evaluated from the seakeeping model test.

However, it was observed that the wave with the pitch forcing period, where the wave length is close to the ship length, is more important than the wave with the maximum wave height after several accidents caused by the green water in Northern North Sea and Norwegian Sea. Therefore, it became a common practice to include not only the wave conditions with maximum wave heights for each return period but also the wave conditions with the pitch forcing period to evaluate the seakeeping performance for offshore development floaters. Ship type floaters such as FPSO are more likely to experience higher impact force due to the large frontal area accompanied by large heave and pitch motions in head sea and bow quartering seas. Recently, it was reported that in an accident in North Sea of UK sector, the damage at the bow of the FPSO is caused due to the steep waves. Afterwards, studies on the steep waves have been made in several institutes such as UK HSE.

In this study, the effect of the impact load (so called slapping load) by the steep waves acting on the FPSO bow is investigated throughout the model test. For measurement of the pressure and impact force on the frontal area, a bow-shaped panel was fabricated with the pressure and force sensors, and installed on the bow starboard side of the model FPSO. During the model test campaign, the impact load was investigated using the steep waves with Hw/λ greater than 1/16 in addition to the general wave conditions with maximum wave heights.

Consequently, it is confirmed in the model test that the impact loads acting on the FPSO bow are significantly increased with the steep waves (Hw/λ > 1/16) compared to the general wave conditions. Therefore, it is necessary to consider whether the steep waves are additionally included in the wave conditions to estimate the seakeeping performance and how to apply the impact loads acting on the FPSO bow from the steep waves in structure design.
Dynamic Coupling Between Top-End Vessel Sway and Slender Riser VIV in Deep Water
Authors: Chen Weimin , Li Min , Guo Shuangxi , Gan Kuan
Published: September 2014

The impacts of top-end motion on the riser undergoing vortex-induced vibration (VIV) are explored in this study, because the dynamic coupling between moving top-end vessel and submarine riser becomes more remarkable for a floating platform in deeper water due to the larger top-end motion amplitude, compared with the fixed platform in shallow water. A coupled hydrodynamic force approach, involving the vortex-induced lift force along with the fluid drag force, is developed. The dynamic responses of the system including a floating top-end and a riser experiencing VIV are examined by means of finite element simulations. The effects of amplitude and frequency of top-end vessel sway on riser VIV are examined. Our numerical results show that the riser displacement becomes several times larger than the displacement for the case without top-end motion. Moreover, the nonlinear response amplification is observed, and the nonlinear amplification gets more pronounced as the number of mode order dropping, while the amplification factor just slightly changes with the increase of sway amplitude.
Prediction of Asymmetric FPSO Roll Using a Frequency Domain Method
Authors: Bigot Fabien , Seah Robert , Derbanne Quentin , de Hauteclocque Guillaume
Published: September 2014

FPSO roll prediction has traditionally been performed assuming symmetric roll damping resulting in identical roll responses from portside and starboard waves. Recent interest in the industry to predict asymmetric roll response, either due to asymmetric mooring and riser configurations or damping devices, has led to the development of time domain models utilizing asymmetric Morison drag elements. Here, a frequency domain methodology has been developed to account for asymmetric bilge keels leading to differing port versus starboard wave roll response. A nonlinear bilge keel drag formulation, that includes the effects of radiation velocity, is used, coupled with linearization techniques, to predict the difference in roll RAO from port versus starboard waves. The drag formulation is initially calibrated against FPSO decay tests before the model is validated against measured model test motions. Thus we show that the methodology proposed is capable of predicting the motions from an asymmetric configuration efficiently, such that it can be utilized in design projects requiring FPSO motions analysis.
Material Property Testing for Finite Element Modelling of Coatings
Authors: Boyd Helen , Karjadi Erwan , Demmink Harm , Ridolfi Guido , Keijzers Han
Published: September 2014

In 2012 and 2013 Heerema Marine Contractors (HMC) performed full installation testing (bend, roller, tensioner and friction clamp) on pipes with different types of coating ranging from three layer polypropylene to thick insulation coating. The material property data as supplied by the coaters and/or the material suppliers appeared to have insufficient details for HMC to develop a model for the coated pipes. In order to obtain the missing details, HMC undertook a program of material finger printing for all coating materials used in the recent full scale testing in order to establish our own baseline for material properties. The reasons for doing so were; i) the data sheets from different suppliers of similar products were based on different test procedures and the results were not directly comparable, ii) initial testing indicated that the results quoted on the data sheets could not always be achieved by HMC and iii) the data as provided by the suppliers appeared to be not sufficient to be used for material models for finite element analysis. The focus to date has been on polyurethane based insulation materials, both for line pipe coating and for field joint coating, although the plan is to continue with polypropylene based insulation materials. The purpose of this paper is to discuss the setup of the full scale level winder and bend tests, the measurements and observations from the tests, the preliminary finite element analyses of the coating and the findings from the finger printing testing to date.
A Multi-Body Algorithm for Wave Energy Converters Employing Nonlinear Joint Representation
Authors: Padeletti Davide , Costello Ronan , Ringwood John V.
Published: September 2014

When large relative displacements take place between the bodies in a multi-body Wave Energy Conversion system linearisation of the constraints on motion imposed by the joints between the bodies is no longer valid and a non-linear time-domain analysis is necessary. As a part of the Techno-Economic Optimisation of Wave Energy Conversion (TEOWEC) software, which has been developed at the Centre for Ocean Energy Research (COER), NUI Maynooth, we developed an algorithm for the dynamic simulation of Multi-Body Systems for Wave Energy Conversion (MBS4WEC) with fully non-linear representation of the body-to-body joints. The algorithm is based on the Joint-coordinate formulation, which provides a systematic procedure to transform the mixed differential-algebraic equations of motion in body coordinates, for open chain systems, to a minimal set of ODEs. When a closed-loop chain occurs, the same method can be adopted by removing one or more kinematic joints from each loop. Knowing the topology of the system, a path matrix is generated and together with the formulation of data structures representing the body-to-body joints, the Velocity Transformation Matrix is computed. The main advantage of this approach is a fast and automatic generation of the Velocity Transformation Matrix, which leads to a higher computational efficiency, especially for complex systems. This paper presents the equations underpinning the method together with results for simulation of two specimen floating multi-body systems. These two are a simple multi-body hinged barge and a device with a sliding internal reaction mass. In each case the results are contrasted to the results produced by a linearised analysis of the same system.
Simulating Minimum Required Power and Manoeuvrability in Adverse Conditions
Authors: Sprenger Florian , Selvik Ørjan , Fathi Dariusz , Ringen Edvard , Hassani Vahid
Published: September 2014

The 2002 IMO regulations regarding the turning, course keeping and stopping ability for vessels with a length greater than 100 m do not cover the presence of waves, wind and current. But their effects may significantly reduce the manoeuvring performance of ships, especially of smaller vessel types in shallow and restricted waters. Since January 2013, an additional IMO regulation is in force, covering the energy efficiency of ships by defining an Energy Efficiency Design Index (EEDI) that must not exceed a specified reference line for any new-built or converted vessel. The reference line to be met will successively be lowered in three steps. One way to meet the EEDI is a reduction of the installed power, which reduces the powering margin and may lead to significant safety issues for some ship types like smaller general cargo vessels since manoeuvring capabilities in adverse conditions might not be sufficient anymore. Due to the unpredictability of waves, a performance assessment is certainly not feasible in full scale and systematic model test series are time consuming and expensive. It is therefore of utmost importance to develop reliable and efficient software tools that are capable to simulate and predict the seakeeping and manoeuvring behaviour of a vessel at the design stage. In this paper, MARINTEK’s combined seakeeping/manoeuvring simulator VeSim is presented, calibrated and successfully validated by model tests with a general cargo vessel. In this software, the vessel hydrodynamics are solved taking care of both the seakeeping and maneuvering problems simultaneously. External forces result from waves, current and wind as well as from e.g. the propulsion system and mooring lines. The pre-calculated hydrodynamic properties of the vessel include speed-dependent resistance, maneuvering forces (mainly viscous), mass and restoring properties, damping and added mass properties (represented as retardation functions) and viscous roll damping. The maneuvering forces are calculated using current and wave particle velocities as input in addition to the ships velocities. A simulation study with VeSim is performed to find the minimum required power for advancing in head seas as a function of wave period and wave height for a general cargo vessel. In addition, two IMO standard manoeuvres — turning circles and 10°/10° zig-zag tests — are simulated in calm water as well as one regular wave condition in order to exemplify the capabilities of VeSim.
Offshore Structural Steel Plates for Extreme Low Temperature Service With Excellent HAZ Toughness
Authors: Ichimiya Katsuyuki , Hase Kazukuni , Endo Shigeru , Terazawa Yusuke , Fujiwara Takaki , Hashimoto Masayuki , Suzuki Shinichi
Published: September 2014

The strength and the toughness required for steel plates used for offshore structures became higher as the installation areas move into arctic areas. The main property of offshore structure steel is the crack tip opening displacement (CTOD) property of weld joint, and CTOD testing is performed at the minimum design temperature of the structure. Thus, the demand for satisfying −40°C of CTOD test temperature specification has increased. For the improvement of HAZ toughness, coarse austenite grain is suppressed by TiN, and low-C, Ceq, Si, P, Nb design is adopted to decrease the formation of M-A constituents. Furthermore, by using Ca inclusion, which works as a pinning particle and a bainite nucleation site, very fine bainite microstructure are formed in HAZ and excellent low temperature toughness are achieved. The YP420 class plate with excellent low temperature toughness has been developed using these technology.
A Numerical Study on Stratified Shear Layers With Relevance to Oil-Boom Failure
Authors: Kristiansen David , Faltinsen Odd M.
Published: September 2014

Interface dynamics of two-phase flow, with relevance for leakage of oil retained by mechanical oil barriers, is studied by means of a 2D lattice-Boltzmann method combined with a phase-field model for interface capturing. A Multi-Relaxation-Time (MRT) model of the collision process is used to obtain a numerically stable model at high Reynolds-number flow. In the phase-field model, the interface is given a finite but small thickness where the fluid properties vary continuosly across a thin interface layer. Surface tension is modelled as a volume force in the transition layer. The numerical model is implemented for simulations with the graphic processing unit (GPU) of a desktop PC. Verification tests of the model are presented. The model is then applied to simulate gravity currents (GC) obtained from a lock-exchange configuration, using fluid parameters relevant for those of oil and water. Interface instability phenomena are observed, and obtained numerical results are in good agreement with theory. This work demonstrates that the numerical model presented can be used as a numerical tool for studies of stratified shear flows with relevance to oil-boom failure.
Local Stress Analysis of Composite Production Riser Under Random Sea
Authors: Singh Manander , Ahmad Suhail
Published: September 2014

The advantage of composite riser is more pronounced due to its light weight and reduced axial tension and bending moment. Its characteristics provide more flexibility in the design of riser system such as stress joint, tensioner or even the platform hull. The composite riser under study consists of alternative hoop and axial layers. There is a marginal coupling between these two orientations hence, the riser is spatially orthotropic. The pressure capabilities of riser are governed by the performance of hoop layers under combined fluctuating axial tension and bending moment. The internal steel liner provided to ensure no leakage often limits the composite riser capabilities. The steel liner provided for production inevitably carries major share of loads. An attempt has been made to carry out a detailed local analysis of a segmental length under critical loads. Damage analysis for various combinations of axial tension and bending moment are performed. The results of global analysis are used to act as boundary/initial condition for the local and detailed dynamic analysis of the segmental length modeled as finite element assemblage of shell elements. The critical stress time histories obtained by global analysis are applied at the local level. The composite layers sustained the random stresses that lead to the failure of the composite. Some realistic failure criteria are chosen to check the damage at local level.
Stability Analysis and Experiment of Large-Scale Spherical Models Built by High Strength Steel
Authors: Du Qinghai , Cui Weicheng
Published: September 2014

The spherical shell is a typical form of revolution shells which are used widely in engineering especially as underwater pressure hull. To disclose structural characteristics of the whole spherical shell with some initial imperfections and residual stresses, both material nonlinear and geometric nonlinear Finite Element Analysis (FEA) has been carried out in this paper. In the FE analysis, the elastic-plasticity stress-strain relations have been adopted and the initial deflection of spherical shell caused in manufacture was also taken into account in creating model. It is also shown that the nonlinear structural characteristics of the spherical shell vary from its different dimension parameters for initial imperfection. Compared with the exiting different rule’s methods, nonlinear FEM may exactly show sphere’s stability varying by initial imperfections. Then two groups of experiments of four spherical models, made by a high strength steel and with two kinds of same main sizes but with different initial deflection on them for manufacture, have been finished in model pressure tests. The experiment has been analyzed by comparing in different method while these results eventually indicate that the buckling stability of a spherical shell model varies by its initial imperfection and such materials sphere critical load could not be accounted for by current rules except nonlinear FEM or modified theoretical elastic-plasticity analysis method. Therefore it is essential to obtain the new analysis and design method for spherical shell made by high strength steel used to deep-sea vehicle or other ocean engineering.
Tidal Current Turbine Wake and Park Layout in Transient Environments
Authors: Arnold Matthias , Cheng Po Wen , Daus Philipp , Biskup Frank
Published: September 2014

Due to orbital velocities of the waves, the characteristics of tidal current turbines change over time. Therefore the induction factor and subsequent the wake is time dependent. Within the present research this time dependency is investigated by using Computational Fluid Dynamics (CFD) with Virtual Free Surface (VFS) and Actuator Disc (ACD) models.

Based on this setup several different wave and current scenarios are simulated and analyzed with respect to the transient velocities in the turbine wake. Special respect is taken to the velocity undulations radiated by the changing apparent velocities in the rotor plane. These undulations move with the wake of the tidal current turbines and increase the wave loads on 2nd row turbines in a park.

This paper presents an efficient method for simulation of wave and park interactions and investigates dynamic turbine wakes under a large variety of parameters. Based on these simulations a suggestion for a tidal park design with respect to a balance of fatigue loads and power output is concluded.
Bilge Keel Forces and Vortex Shedding: A Numerical Analysis With OpenFOAM
Authors: Piehl Henry , el Moctar Ould
Published: September 2014

The damping effectiveness of a bilge keel depends on the velocity of the flow and the roll period of the ship. The Morison equation defines the relation between these motion parameter and the forces acting on the bilge keel. Sarpkaya and O’Keefe published in 1996 an article with their results of several flow experiments conducted over a wide range of Keulegan-Carpenter period parameter. They provide the KC dependent drag and inertia coefficients obtained from the measured forces on a bilge keel and discuss the vortex pattern generated by the oscillating bilge keel.

In the present study the CFD code OpenFOAM was used to compute the flow around a bilge keel and the related forces. The numerical and experimental results are compared. Based on the test conditions a finite volume mesh was generated and the flow was computed with a transient, turbulent flow solver. In order to investigate the boundary layer on an oscillating wall and the dissipation of the vortex structures different turbulence models (kωSST, low Re and LES) were used. The experiments were conducted at zero forward speed. However, the computations were performed for different ship speeds.
Green Water on FPSO Predicted by a Practical Engineering Method and Validated Against Model Test Data for Irregular Waves
Authors: Schiller Rafael Vergara , Pâkozdi Csaba , Stansberg Carl Trygve , Yuba Douglas Gustavo Takashi , de Carvalho e Silva Daniel Fonseca
Published: September 2014

This paper presents a series of numerical analyses performed with the potential theory-based Green Water engineer tool KINEMA3. KINEMA3 was designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in design load analysis. The purpose of the study presented herein is to validate KINEMA3 green water (deck overtopping) predictions in nonlinear irregular waves with results from model tests performed at the TPN (Tanque de Provas Numérico) laboratory at the University of São Paulo, Brazil. Comparisons are made for a selection of irregular wave cases, for two choices of anchoring conditions (free floating vessel and fixed vessel) and for three wave headings (180°, 225° and 270°: head, quartering and beam seas, respectively).

KINEMA3 statistical green water predictions present a general good agreement with observations from the TPN model tests for all wave cases, headings and mooring conditions. Overall, observed trends for occurrence of green water and standard deviation/maximum of relative wave height are successfully reproduced by KINEMA3. In agreement with model test results, it is predicted that green water occurs more frequently for a free floating vessel and for beam seas.

Additional comparisons between KINEMA3 predictions using different FPSO panel models (low-order and high-order models) present negligible differences with respect to green water estimates. The results presented herein demonstrate the robustness of the tool towards the prediction of green water for variable wave headings and sea states, and highlight the capability of KINEMA3 to be employed as an engineering-like tool for fast and multiple estimates of green water in early design studies.

This work is a part of the research project “Green Water and Wave Impact on FPSO” carried out for and in cooperation with PETROBRAS.
Green Water and Wave Impact on FPSOs in Santos Basin: Challenges and Prediction Tools
Authors: Schiller Rafael Vergara , Pâkozdi Csaba , Stansberg Carl Trygve , de Carvalho e Silva Daniel Fonseca
Published: September 2014

Green water (water-on-deck) and subsequent wave impact is a strongly non-linear, random and complex phenomenon that represents an important factor to be considered in the design of moored vessels and vessels in transit. The Santos Basin, in southeast Brazil, is a new frontier for deep water oil production, where FPSO green water issues are expected to be more important. In this paper, we investigate new green water challenges associated with the Santos Basin. We employ an engineering prediction tool, KINEMA, designed to predict wave-induced impact loads on FPSOs in steep irregular waves, and for use in early design load analysis. We perform a sensitivity study to arbitrary wave directions and present preliminary results from a case study that would be illustrating for the Santos Basin.

Firstly, a comparison between numerical green water predictions and a set of earlier model test data for a Campos Basin case shows satisfactory agreement. A sensitivity study suggests that an empirical tuning factor, which is related to wave amplification and wave-structure interaction, should decrease with increasing wave heading. Then, a preliminary numerical investigation of the green water problem in Santos Basin wave conditions demonstrates that although the wave impact from the largest waves (S-SW) may be avoided by heading the vessel towards S-SW, other wave directions have to be taken into consideration. The results presented herein confirm that multi-directional wave heading is a green water challenge in the Santos Basin. Further studies that address this problem in detail, in special variations in the wave-structure interactions due to wave heading, and for actual particular Santos Basin FPSO’s, are recommended.
Hydrodynamic Performance of an S-SWATH Ship in Calm Water and Waves
Authors: Qian Peng , Yi Hong , Li Yinghui
Published: September 2014

An unconventional SWATH (Small-Waterplane-Area-Twin-Hull) ship is introduced, named S-SWATH, which is a catamaran with twin hulls that are slightly curved in an S-form and arranged at a mean yaw angle but mirror symmetric to their common longitudinal center plane. Based on the “shallow-channel superconductivity” theory, proposed by Chen and Sharma, in this paper a more accurate viscous flow theory, solving the Reynolds-averaged Navier–Stokes equations (or RANS equations), is used to study the hydrodynamic performance of the S-SWATH ship. The simulation results of calm-water resistance and motions in waves are presented. In comparison with a benchmark conventional SWATH ship, which features a typical torpedo-shaped body, the simulation results prove the effectiveness of the S-shape design. On one hand, the S-SWATH ship inherits the major advantages of SWATH ships, such as the superior ride quality, acceptable acceleration levels for human habitability and therefore comfort and overall superior seakeeping characteristics. On the other hand, the S-SWATH ship has much less low-speed drag than its conventional SWATH counterpart, and comparable total drag at high speeds.
HAM Solutions for Vortex-Induced Vibration of a Circular Cylinder
Authors: Lin Zhiliang , Tao Longbin
Published: September 2014

The vortex-induced vibration (VIV) phenomenon is result of fluid-structure interaction which occurs in many engineering fields. The study of VIV of a circular cylinder is of practical importance (such as in marine cables and flexible risers in petroleum production). In this paper, one classical phenomenological VIV model — the motion of the cylinder is modeled by a simple linear equation, and the fluctuating nature of the vortex wake oscillation is modeled by a van der Pol oscillator, is analyzed. Firstly, the homotopy analysis method (HAM), a powerful technique for highly nonlinear problems, is developed to solve the coupled fluid-structure dynamical system with the convergence of the homotopy series solutions being demonstrated. Based on the HAM solutions, some properties of the fully nonlinear classical coupled VIV model are presented. All the results proved that the proposed HAM scheme has potential to be an effective analytic technique to study the VIV problems.
Carcass Tear Out Load Model for Multi-Layer Pressure Sheath Risers
Authors: Kristensen Claus Egebjerg , Muren Jan , Skeie Geir , Skjerve Håvard , Sødahl Nils
Published: September 2014

Recent failures of multi-layer pressure sheath risers have shown that the carcass may fail in the top termination due to excessive axial loads. This is a new failure mode for flexible risers, recently presented by the authors in more general terms. The present paper explains details of the established load model and the validation against mid-scale tests, risers failed during operation, and operating risers close to failure by this new mode. The key driver in the model is the temperature contraction of pressure sheath layers. Also influenced by changes in polymer properties over the operational history, temperature and time is explained. Other contributing factors in the load model are gravity-component and bore pressure.

The prediction model for the carcass loads are developed during Statoils investigation in 2011–12. The model is regarded representative for 20% of the most exposed risers. Several of the input parameters are uncertain and a Monte Carlo simulation approach is selected to study the variability and predict the probability of failure, given that radial contact pressure is sufficiently low.

The approach adopted in the model may be applicable to other risers where polymers and steel components act together, and in such circumstances act as a guide for alternative model developments.
Results From Numerical Simulation and Field Tests of an Oceanographic Buoy Powered by Sea Waves
Authors: Hamilton J. A. , Henriques J. C. C. , Cazenave F. , McGill P. , Radochonski W. , Falcão A. F. O. , Gato L. M. C. , Gomes R. P. F.
Published: September 2014

The paper presents a performance analysis of a wave-energy converter designed for oceanographic applications to generate 300–500 W of electrical power on average. The prototype consists of a small draft cylindrical buoy connected to a submerged anti-heave plate by a hydraulic power takeoff system and cable. Engineering details and design of the system are based on the results of a detailed time-domain hydrodynamic analysis of the system, discussed here. The performance of the prototype is assessed with respect to the submerged plate size/added-mass and the effectiveness of latching schemes. Additionally, results for the power extraction are statistically compared with measurements performed during field tests in Monterey Bay, California. During these tests performance measurements were logged by the buoy, and wave data was recorded by a measurement buoy positioned 1 km from the deployment site. This allows the comparison of actual performance to model predictions run for the sea state present during testing. In general, the results of the numerical model match fairly well with the data acquired in field testing. The proposed causal latching control schemes have been shown to be ineffective for this type of wave-energy converter.
Control-Influenced Layout Optimization of Arrays of Wave Energy Converters
Authors: Balitsky Philip , Bacelli Giorgio , Ringwood John V.
Published: September 2014

In this paper we compare the optimal configurations for an array of WECs given two control schemes, a real-time global control and a passive sea-state based tuning scheme. In a particular wave climate and array orientation with its axis normal to the prevailing wave direction, closely-spaced symmetrical arrays of 2, 3, 4, 5, and 6 cylinders of different radiative properties are simulated for varying inter-device separation distances. For each device and control type, we focus on the factors that influence the optimal layout, including number of devices, separating distance and angular spreading. The average annual power output is calculated for each optimal configuration.
Integrity Assessment of Damaged Flexible Pipe Cross-Sections
Authors: Ji Guomin , Leira Bernt J. , Sævik Svein , Klæbo Frank , Axelsson Gunnar , Fergestad Dag
Published: September 2014

This paper presents results from a case study performed to evaluate the residual capacity of a 6″ flexible pipe when exposed to corrosion damages in the tensile armour. A three-dimensional nonlinear finite element model was developed using the computer code MARC to evaluate the increase in mean and dynamic stresses for a given number of damaged inner tensile armor wires. The study also includes the effect of these damages with respect to the associated stresses in the pressure spiral. Furthermore, the implications of a sequence of wire failures with respect to the accumulated time until cross-section failure in a probabilistic sense are addressed.
Differential Equation for Evaluating Transverse Buckling Behavior of Tensile Armour Wires
Authors: Sævik Svein , Ji Guomin
Published: September 2014

The present paper addresses aspects related to transverse tensile armour buckling in flexible pipes. An analytical model for evaluating the tensile armour buckling capacity is presented based on formulating the linearised differential equation describing the transverse stability of the thin curved wire assuming no friction. This is followed by a numerical study based on FE analysis to evaluate the extra capacity from friction during cyclic bending behaviour and where the yield stress is used as the failure criteria. The results is then compared to test data and a design criteria for transverse tensile armour buckling proposed.