bluuebunny/crossref_metadata_2025 huggingface dataset:
Making Sense of 3D Printing/Additive Layer Manufacturing in Offshore Petroleum Industry: State of the Art
Authors: Ratnayake R. M. Chandima
Published: October 2016

Three-dimensional printing (3DP)/additive layer manufacturing (ALM) allows the cost-effective and fast fabrication of parts with intricate/complex external and internal structure via the addition of material layer-by-layer in a controlled environment. Hence, 3DP/ALM related technology has a significant potential to mitigate most spare parts related challenges present in the offshore petroleum industry. That is especially the case in offshore petroleum operations in remote locations and harsh environments (e.g. Arctic operations), when parts can be printed on-site upon demand. Digitalized and localized supply chains enable the minimization of delivery lead-times. This is vital when there is a significantly large lead-time involved for spare parts to come from a warehouse or manufacturer. Putting multiple parts together into one minimizes future inspection and maintenance challenges, where, without 3DP/ALM, it is too expensive or impossible to produce with the existing conventional manufacturing approaches. Mass customization and 3D visualization allow industry leaders, engineers and technicians to gain a better understanding of the equipment operation. This manuscript provides a comprehensive investigation of the potential to use 3DP/ALM in general and within the offshore petroleum industry. In addition, it suggests a methodology for investigating optimal parameter settings (i.e. designing of parameter combination) when a 3DP/ALM machine supplier’s manual does not specify the parameter combinations for a certain metal and/or when the end-product requirements demand certain metallurgical properties and mechanical characteristics.
Comparative Study of Dynamics of Gravity Cages With Different Meshes in Waves and Current
Authors: Wang Xinxin , Wan Rong , Zhao Fenfang , Huang Liuyi , Sun Peng , Tang Yanli
Published: October 2016

To investigate the dynamics of gravity cage, the finite element program Aqua-FE™, was applied to gravity cages with two different meshes, square-mesh net and diamond-mesh net. Two case studies are chosen to compare the dynamics of cages based on the numerical modeling techniques. The numerical models were developed in Aqua-FE™ to simulate the effects of waves and current. They were validated by comparison with water tank results. The comparison showed good agreement. In both case studies, we consider several loading conditions consisting of different uniform currents and monochromatic waves. Assuming that the system can be modeled as a linear system, we investigated the motion response (heave, surge and pitch) characteristics of the fish cages with square-mesh net and diamond-mesh net, their deformation and the resultant tension in mooring lines. For different wave conditions, we study the storm response of the two cages based on the response amplitude operators (RAOs). In particular, the length of the grid line has significantly effect on the motion of the cage and the tension in mooring lines in wave. In additional, the effect of the mesh shape on the motion of the cage and tension in mooring lines is also analyzed. The comparison results show that the surge motion of the fish cage with square-mesh net is significantly larger than that with diamond-mesh net.
Experimental Investigation of Wave Loads Based on Trimaran Self-Propulsion Model
Authors: Xiaobo Wei , Ren Huilong , Sun Yanlong , Wang Di , Wang Zhen Yu
Published: October 2016

Trimaran, as a high performance ship, its special ship form is different from regular monohull ship. The particular characteristics of longitudinal and transverse wave loads are concerned greatly by ship structure designers. Theoretical methods for forecasting the wave loads of trimaran are under developing. And the relative comprehensive model test study of trimaran’s wave loads is rare in the publication. In this paper, the trimaran model test had been carried out in the tank. According to similarity theory and simulation of stiffness, a scale model of trimaran with measurement system had been manufactured. Then the segmented model had navigated in regular waves of different sea conditions. Through analysis of the experimental data, the wave loads characteristics of this trimaran are presented. A comparison of test results and theoretical values is also made to show the similarities and differences. This study can provide some useful information for further design of high-speed trimaran in the point of wave loads, which maybe a reference for research of trimaran.
A Review on Damage Identification and Structural Health Monitoring for Offshore Platform
Authors: Sun Liping , Lu Yang , Zhang Xinyue
Published: October 2016

Structural health monitoring (SHM) based on vibration measurements in large/complex structures were shown to be promising by researchers. The authors believe that the SHM problem is fundamentally one of statistical pattern recognition. Therefore, the damage detection studies reviewed herein are summarized in the context of a statistical pattern recognition paradigm[1]. This paradigm can be described as a three-part process: (1) Data acquisition and cleansing, (2) Modal parameter identification, (3) Damage identification methods. However, offshore platform structures are very complex, and not easy to excite artificially and they are often suffered from ambient loads that cannot be controlled easily. The thesis focuses on three key issues for structural health monitoring via vibration in real offshore platform structures[2].

In the first part of review, the offshore platform structure health monitoring system basic principle and the composition are discussed. In the second portion, three important processes of structure health monitoring are summarized (Data acquisition and cleansing, modal parameter identification, damage identification methods), and each method good and bad points is pointed out. Next, Application of damage identification and structural health monitoring to offshore platform are in detail produced, the methods are described in general terms including difficulties associated with their implementation. Finally, current and future-planned applications of this technology to offshore platform are summarized. The paper concludes with a discussion of critical issues for future research on damage identification and structural health monitoring for offshore platform.
Numerical Study of Wake-Induced Vibrations for Cylinders in Tandem With Different Diameters at High Reynolds Numbers
Authors: Nguyen Vinh-Tan , Chan Wai Hong Ronald , Nguyen Hoang-Huy
Published: October 2016

Wake induced vibration is a distinctive phenomena of fluid-elastic instability arising from interactions of a body in the wakes of another bluff body and characteristically different from the well-understood vortex induced vibrations. This work presents a fluid-structure interactions numerical model as an alternative tool for investigation of wake induced vibrations. In an attempt to better understand mechanisms of wake induced motions, a simplified model of two cylinders in tandem arrangement with different diameters under cross flow was considered in this work. Cross flow velocity conditions vary from moderate to high Reynolds number (Re = 2 × 103–5 × 104) in the same range as many experiment reported recently in literature. A hybrid detached eddy simulation approach is used for turbulence modelling at those high Reynolds number conditions in order to resolve complex near body flow features as well as in the wake regions. The proposed model is first validated through extensive benchmarking with experimental studies for responses of tandem cylinders at the same flow conditions as in physical experiment. With good agreement to experimental data, the model was extended for simulations of cylinders of different diameters in tandem arrangement. For different diameters between upstream and downstream cylinders, the fundamental frequencies of shedded vortices from the cylinders are essentially different. It is observed from the present study that responses of the downstream cylinder are characterized not only the geometrical parameters such as distances and diameter differences between the cylinders but also the Reynolds number. As contrast to many experimental studies, at constant Reynolds number, downstream cylinders are found to have multiple lock-in regions in a wide range of reduced velocities. This distinctive behaviour of the cylinders at constant Reynolds numbers and diameter ratios suggests strong evidence of complicated mechanism of wake-induced vibrations phenomena. Further analysis of results from high fidelity numerical simulations were carried out for detailed investigations of force amplitudes and frequencies. The current analysis revealed multiple frequency content of the force; thus explaining high response amplitudes of the downstream cylinder at high reduced velocity.
Pure Bending Behavior of Pipe Reinforced by Steel Wires (PSP)
Authors: Tang Gao , Ruan Weidong , Huang Ting , Lu Yutian , Bai Yong
Published: October 2016

Plastic pipe reinforced by helically cross-winding steel wire (PSP) is a composite pipe, which is being applied into the offshore oil and gas industry. However, PSPs are often subjected to bending loading during the reeling process and offshore installations, which may lead to elliptical buckling due to the Brazier effect. Thus the ovalization instability of PSP under pure bending was investigated in this paper. According to the nonlinear ring theory, the ovalization growth of cross section during bending was studied. Then, the formulation was developed based on the principle of virtual work and was efficiently solved by Newton-Raphson method. Besides, a simplified method was proposed to simulate the behavior of steel wire reinforced layer. To verify the accuracy of the theoretical method, an ABAQUS model was employed to simulate the buckling response of PSP under pure bending. The results obtained from the theoretical method were compared with ABAQUS simulation results, and they show excellent agreements. The results can be used for predicting PSP’s bending behavior in offshore engineering applications.
Behavior of Flexible Pipe Subjected to Internal Pressure
Authors: Yuan Shuai , Ruan Weidong , Han Peihua , Bai Yong , Cheng Peng
Published: October 2016

The increasing use of flexible pipes in subsea with high pressure/high temperature brings about much more challenges. Although there has been a simple prediction method for burst pressure, a more comprehensive prediction of the ultimate strength of flexible pipe subjected to internal pressure is essential for the safe use of flexible pipe under complex environments in terms of different failure modes. In this paper, based on the principle of virtual work, a theoretical model for stresses and deformations of the pipe under the short-term internal pressure have been developed and the obtained results have been compared with the ones from the FEM which is used to simulate the pipe under increasing internal pressure using ABAQUS. And the mechanical properties of two kinds of armor layers have been studied comprehensively considering different boundary conditions. The results and FEA models can be useful for the design of flexible pipes. Finally, the failure prediction of a complete model is discussed.
Numerical Simulation and Experimental Validation on the Surf-Riding and Broaching of a Fishing Vessel
Authors: Yu Liwei , Ma Ning , Fan Sheming , Feng Peiyuan , Gu Xiechong
Published: October 2016

Model experiments and numerical simulations on the surf-riding and broaching in following seas of a 42.5m long purse seiner are conducted. Firstly, the free running model experiments with various ship speeds and wave heights are performed in the towing tank to reproduce the phenomena of surf-riding and broaching. Then, the 6-DOF weakly nonlinear unified model is applied to simulate the motions of the purse seiner with the same cases as the model experiments. Through the comparison between results of model test and numerical simulation, the occurrence conditions of periodic motion, surf-riding and broaching are roughly determined. Finally, it is found that although it is difficult for the numerical simulations to get the same time histories as model tests, the modes of motion (periodic motion, surf-riding or broaching) obtained from the numerical simulations agree well qualitatively and quantitatively in part with the model test results.
Dynamic Decision-Making Model for Traffic Organization Within Traffic Separation Scheme During Maritime Accident Process
Authors: Wu Bing , Yan Xinping , Wang Yang
Published: October 2016

The traffic organization within traffic separation scheme can be generally treated as a trade-off between shipping efficiency and maritime safety. As the maritime accident development is widely accepted as a process including initiating event, mid-event and end event, the traffic organization during this process should not only consider the current situation but also the future situation. In order to address this problem, a dynamic decision-making method, where time is treated as dependent, is proposed in this paper. The kernel of the proposed approach is to analyze the sequence of accident using event tree, to establish a dynamic decision-making method with decision matrix of multiple states, and to make final decision by introducing Technique for Order Preference by Similarity to an Ideal Solution. The result is also compared with the traditional time independent decision-making, which makes decisions only with the current data. Consequently, the dynamic decision-making method can make a comprehensive and feasible solution to traffic organization during maritime accident process.
Optimal Vertical Position Control of a Near-Surface Remotely Operated Vehicle in Regular Waves
Authors: Liang Xiaoyang , Liu Han , Ma Ning , Hirakawa Yoshiaki , Gu Xiechong
Published: October 2016

Precise vertical positioning has a very significant impact on the accuracy and reliability of the Remotely Operated Vehicle (ROV) working process. This paper establishes an experimental system which is capable of controlling and measuring the vertical position of ROV. The control signal output system is developed by integrating certain modules such as video recording, image-analog-digital signal converting, timing depth calculating and force signal outputting modules. The effects of Proportional-Integral-Derivative (PID) method on ROV depth control in still water and under various regular waves was tested and compared. The causes of difference of control effect between in still water and in waves were analyzed. Giving insight into the hydrodynamic characteristics and consequent movement of ROV, a practical underwater vehicle maneuvering mathematical model was established. The space motion equations were set up to solve the underwater vehicle maneuvering problem. The effects acted on the carrier by the waves were analyzed in order to develop a feasible control strategy that is applicable to the practical operation. Unsatisfactory effects of thrust output are optimized with MATLAB simulation based on ITAE criterion, using the simplex method for re-tuning PID parameters. Experimental results show that the system for measuring and controlling the vertical position of the ROV is successful. With an appropriate time interval for data collecting, the ROV model’s vertical depth can be effectively determined by the program written in VB language in the still water and small wave height situation. While the wave height increases or the wave period changes, the program needs to be adjusted. Simulation results also show that the wave frequency response abates as the wave period decreases. Compared to the original PID parameters, the new ones can rapidly give response to the vertical position change and guarantee the stability of ROV depth controlling. It is of obvious importance to actual control of the underwater vehicles’ vertical movement with the help of mathematical optimization method for the controller parameters. The proposed controlling algorithm can be an alternative for other similar working conditions.
Experimental Investigation on the Dynamic Response of a Three Legged Articulated Type Offshore Wind Tower
Authors: Joy Chinsu Mereena , Joseph Anitha , Mangal Lalu
Published: October 2016

Demand for renewable energy sources is rapidly increasing since they are able to replace depleting fossil fuels and their capacity to act as a carbon neutral energy source. A substantial amount of such clean, renewable and reliable energy potential exists in offshore winds. The major engineering challenge in establishing an offshore wind energy facility is the design of a reliable and financially viable offshore support for the wind turbine tower. An economically feasible support for an offshore wind turbine is a compliant platform since it moves with wave forces and offer less resistance to them. Amongst the several compliant type offshore structures, articulated type is an innovative one. It is flexibly linked to the seafloor and can move along with the waves and restoring is achieved by large buoyancy force. This study focuses on the experimental investigations on the dynamic response of a three-legged articulated structure supporting a 5MW wind turbine. The experimental investigations are done on a 1: 60 scaled model in a 4m wide wave flume at the Department of Ocean Engineering, Indian Institute of Technology, Madras. The tests were conducted for regular waves of various wave periods and wave heights and for various orientations of the platform. The dynamic responses are presented in the form of Response Amplitude Operators (RAO). The study results revealed that the proposed articulated structure is technically feasible in supporting an offshore wind turbine because the natural frequencies are away from ocean wave frequencies and the RAOs obtained are relatively small.
Study of Surface Wave Characteristics and Extreme Parameters Estimation in a Port With Submerged Breakwater
Authors: Wang Zhifeng , Dong Sheng , Dong Xiangke , Zhang Xin
Published: October 2016

Surface waves are simulated and extreme parameters are calculated in Weifang Port in this paper. Firstly, wind data of every 3 hours from 1985 to 2010 in the Bohai Sea are simulated by Weather Research Forecast Model (WRF). Then wave elements such as significant wave height, wave period and wave direction are simulated every 1 hour from 1985 to 2010 by SWAN model in the whole of Bohai Sea. By comparison and validation, both the simulation wind data and wave data show a good agreement with the observation data. Extreme parameters of wind speed, wave height and wave period in every direction are calculated according to Pearson-III distribution at the −15m isobath in Laizhou Bay. The results show that the strong wind and wave are in direction N, NNE and NE. Surface waves are calculated using MIKE21 SW to study wave propagation from the open sea to the coast. The wave elements inside of the submerged breakwaters are calculated by three empirical formulas. The results from the three formulas are different, and the conservative result is chosen considering engineering safety.
Burial and Scour of Short Cylinders and Truncated Cones due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Currents
Authors: Ong Muk Chen , Myrhaug Dag
Published: October 2016

This paper provides a practical stochastic method by which the burial and scour depths of short cylinders and truncated cones exposed to long-crested (2D) and short-crested (3D) nonlinear random waves plus currents can be derived. The approach is based on assuming the waves to be a stationary narrow-band random process, adopting the Forristall [1] wave crest height distribution representing both 2D and 3D nonlinear random waves. Moreover, the formulas for the burial and the scour depths for regular waves plus currents presented by Catano-Lopera and Garcia [2, 3] for short cylinders and Catano-Lopera et al. [4] for truncated cones are used.
A FEM Based Potential Theory Approach for Optimal Ice Routing
Authors: Piehl Henry , Milaković Aleksandar-Saša , Ehlers Sören
Published: October 2016

Shipping in ice covered regions has gained high attention within recent years. Analogous to weather routing, the occurrence of ice in a seaway affects the selection of the optimal route with respect to the travel time or fuel consumption. The shorter, direct path between two points — which may lead through an ice covered area — may require a reduction of speed and an increase in fuel consumption. A longer, indirect route, could be more efficient by avoiding the ice covered region. Certain regions may have to be avoided completely, if the ice thickness exceeds the ice-capability of the ship.

The objective of this study is to develop a computational method that combines coastline maps, route cost information (e.g. ice thickness), transport task and ship properties to find the optimal route between port of departure A and port of destination B.

The development approach for this tool is to formulate the transport task in form of a potential problem, solve this equation with a finite element method and apply edge detection methods and line integration to determine the optimal route. The functionality of the method is first evaluated with simple test problems and then applied to realistic transport scenarios.
Taking Further the Domain of Use of Low Plasticized High Molecular Weight PVDF for Monolayer Dynamic Application in Flexible Pipe
Authors: Epsztein Thomas , Demanze Frederic
Published: October 2016

Flexible pipes have been used to transport oil and gas in subsea applications for more than 40 years. Since 2010, and following a significant qualification work performed within Technip flexible pipe technology center, it has been possible to use a low plasticized high molecular weight PVDF with enhanced mechanical properties as monolayer pressure sheath in flexible pipe applications. This qualification work covered both static and dynamic applications. A large number of projects have already taken advantage of the monolayer design for high temperature applications. Indeed, more than 80km of flexible pipe with this PVDF grade have already been manufactured.

This paper will present the work that has been carried out during the last 5 years in order to extend the qualified domain of use of this PVDF grade:

-Maximum design temperature extended from 130°C to 150°C,

-Minimum design temperature extended from −20°C to −30°C,

-Design pressure extended up to 17.5kPsi.

A specific focus will be made on the results obtained on several tests performed at lab scale and on full scale flexible pipes and which have been used to support this extension of the domain of use.

Such tests include the verification of the PVDF grade to sustain rapid gas decompression after exposure to gas medium at high pressure (> 17.5kPsi) and high temperature (150°C). Permeation tests have also been performed at 150°C.

Four full scale tests have been performed on a 6″ flexible pipe with design pressure equal to 17.5kPsi. The first test was performed on a flexible pipe sample submitted to a hydrostatic pressure test at a pressure reaching 27.5kPsi. The second test was performed on a flexible subjected to a fatigue test (tension and angle variation) simulating flexible pipe loading in operating conditions. A burst test was performed on a third flexible pipe sample. During this test, a burst pressure equal to 37.9kPsi was reached. Finally, a fourth flexible pipe sample was tested through the realization of a large number of large bending cycles while keeping the flexible under internal pressure.

The possibility to use this PVDF grade with enhanced mechanical properties down to −30°C has been demonstrated through the realization of thermal cycles between 150°C and −30°C on two flexible pipe samples. This test is realized in order to confirm sealing efficiency towards thermal stresses which occur during shutdowns. The result of a specific full scale test performed, after ageing at 150°C, in extreme conditions of bending and temperature (lower than −30°C) will also be presented.

This extension of the qualified domain of use enables the use of flexible pipes in harsher applications, and also further substantiates the robustness for the use of this grade within the initial qualification domain.
Integrity Assessment of Hot Bolting Tool
Authors: Ji Guomin , Karimirad Madjid , Klæbo Frank , Irgens Per-Christian
Published: October 2016

Hot Bolting is the practice of removing and replacing or freeing and re-tightening bolts on live operating piping and equipment while the system is pressurized. It is potentially hazardous and the utmost caution needs to be exercised when planning and carrying it out. The hot bolting tools designed by Irgens Engineering AS aim to establish a safe barrier for flange connections during the hot bolting operation. Their application would extend the hot bolting operation, increase the safety and simplify the working process. Qualification of new hot bolting tools was carried out by the joint efforts of producer, operator and classification society. The paper addresses a part of the integrity assessment of the new hot bolting tools. The nonlinear finite element analyses were performed by ABAQUS for sequential loading during hot bolting operation under the temperature specified by operator and the nonlinear contact interactions between different components were taken into account in the analysis. In the present study, the structural integrity was investigated for 4″ class 1500 flange with ring gasket and class 150 flanges with IFG gasket of four different dimensions (1/2″, 1.5″, 3″, and 8″). The gasket stress and strain as well as contact pressure of the gasket were studied to investigate the possible leakage. The test was performed for 4″ class 1500 flange with ring gasket by Irgens Engineering AS, and the comparison between analysis and test results showed good agreement both for the gap between flange just outside ring gasket and the flange bolt force.
Loads on a Jacket-Supported Wind Turbine During Hurricane Sandy Simulation
Authors: Kim E. , Manuel L.
Published: October 2016

The dynamic response of a jacket-supported offshore wind turbine under coupled wind, wave, and current fields during Hurricane Sandy is the subject of this study. To illustrate the detailed procedure related to the response evaluation of a 5-MW offshore wind turbine with a jacket support structure, we consider a single site where the water depth is 50 m. Loads are computed using two simulation tools, FAST and Abaqus, with partial coupling. Aerodynamic loads on the turbine rotor are first evaluated using a wind turbine model in FAST with a fixed base; then, these rotor aerodynamic loads are applied as point loads at the top of a model of a tower that is supported by a jacket structure in Abaqus. Based on stochastic simulations, we discuss the applicability of the Abaqus jacket modeling and describe the characteristics and comparisons of the aerodynamic and hydrodynamic effects on loads on the jacket members. Details related to the structural model and soil-pile interaction model employed in the analyses are also discussed.
Oscillating Wave Surge Converter Forced Oscillation Tests
Authors: Crooks David , Hoff Jos van ’t , Folley Matt , Elsaesser Bjoern
Published: October 2016

Hydrodynamic numerical models of Wave Energy Converters (WEC) contain hydrodynamic coefficients that are commonly obtained from numerical codes that solve linear potential flow problems using Boundary Element Methods (BEM codes). The assumptions made by the BEM codes in their calculation of the linear hydrodynamic coefficients are violated by the large and nonlinear motions that wave activation body class WECs often go through during operation. In this study, Forced Oscillation Tests were used to evaluate the hydrodynamic torque coefficients estimated for an Oscillating Wave Surge Converter (OWSC) WEC by two BEM codes; WAMIT and Nemoh. The paper describes the tests and the active Force Feedback Dynamometer test rig used to perform them. The results indicate good agreement between the BEM codes and experimental data for small angular displacement amplitude oscillations, as expected; up to 0.3 rad. The torque not predicted by the BEM codes is presented and shown to have an amplitude and phase that vary throughout the range of tests performed.
Flow-Induced Vibrations of a Square Cylinder With Combined Translational and Rotational Oscillations
Authors: Miyanawala T. P. , Guan Mengzhao , Jaiman Rajeev K.
Published: October 2016

In this work, we investigate the combined translation and rotational flow-induced vibration (FIV) of elastically mounted square cylinder in a free-stream at zero incidence angle. We employ a partitioned iterative scheme to solve coupled fluid-rigid body interaction using unstructured grid. The fluid-solid coupled solver and the mesh is verified by investigating pure translational motion cases at zero incidence against published data for a laminar flow past a square cylinder. Further analysis revealed that the increase of mass ratio shifts the lock-in to higher reduced velocity region. The influence of of the torsional motion parameters is analyzed for a pure rotational case. The combined 3-DOF motion is next considered while keeping the above two analyses as reference. It was evident that, even small yaw vibrations adds circulation to the flow and thus increases the vortex intensity. This phenomenon is identified to be responsible for the differences of motion parameters between the isolated DOF cases and combined 3DOF cases. Finally, for the completeness of the study, the influence of 3D effects is estimated for the same geometry and also a high Re case is presented.
Two Dimensional Linear Irregular Wave Propagation by FMBEM
Authors: Shen Wanggang , Lin Zhiliang
Published: October 2016

In this paper, Fast Multipole Boundary Element Method (FMBEM) is developed to build a numerical wave tank, which is used to simulate a linear irregular wave train. Comparison is illustrated between the simulated and theoretical waves to validate the precision of FMBEM. Furthermore, the time consumptions of FMBEM are also compared with the traditional BEM to demonstrate its high efficiency. Besides, this effective numerical method is used to simulate the wave propagation with the influence of a fixed surface piercing body. All the results demonstrate that the proposed method is an effective numerical technique to study the linear irregular wave propagation with both high accuracy and efficiency.
Study of Water Impact and Entry of a Free Falling Wedge Using CFD Simulations
Authors: Kamath Arun , Bihs Hans , Arnsten Øivind A.
Published: October 2016

Many offshore constructions and operations involve water impact problems such as water slamming onto a structure or free fall of objects with subsequent water entry and emergence. Wave slamming on semi-submersibles, vertical members of jacket structures, crane operation of a diving bell and dropping of free fall lifeboats are some notable examples. The slamming and water entry problems lead to large instantaneous impact pressures on the structure, accompanied with complex free surface deformations. These need to be studied in detail in order to obtain a better understanding of the fluid physics involved and develop safe and economical design. In the special case of free-fall lifeboats, model testing can be expensive and time consuming. Here, numerical modelling can make useful contributions to the design process. The slamming of a free falling body into water involves several complex hydrodynamic features after its free-fall such as water entry, submergence into water and resurfacing. The water entry and submergence lead to formation of water jets and air cavities in the water resulting in large impact forces on the object. In order to evaluate the forces and hydrodynamics involved, the numerical model should be able to account for the complex free surface features, the instantaneous pressure changes around the lifeboat and accurately evaluate the loads on the lifeboat. As a step towards simulating free-fall lifeboats, water entry of a free-falling wedge into water is studied in this paper using a CFD model. The vertical velocity of the wedge during the process of free fall and water impact are calculated for different cases and the free surface deformations are captured in detail. Numerical results are compared with experimental data and a good agreement is seen. The open-source CFD model REEF3D is used in this study. The model solves the Reynolds-Averaged Navier-Stokes equations to evaluate the fluid flow. The convective terms are discretized using a 5th-order conservative finite difference WENO scheme. Time discretization is carried out using a 3rd-order Runge-Kutta scheme. Pressure discretization is carried out using Chorins projection method. The Poisson pressure equation is solved using a pre-conditioned BiCGStab algorithm. A sharp representation of the free surface is obtained using the level set method. The falling wedge is represented using the level set paradigm as well, avoiding the need for re-meshing during the simulation. Turbulence modeling is carried out using the k-ω model. Computational performance of the numerical model is improved by parallel processing using the MPI library.
Application of Reliability Analysis to Re-Qualification and Life Extension of Floating Production Unit Moorings
Authors: Rosen J. , Johnstone D. , Sincock P. , Potts A. E. , Hourigan D.
Published: October 2016

Life extension and asset integrity of Floating Production Unit (FPU) moorings are issues of increasing importance for operators due to changing production requirements, the requirement to extend service life, and circumstances where the met-ocean Basis of Design (BOD) has increased significantly over the life of the field. Reliability methods are gaining increasing acceptance as increased computing power allows large numbers of simulations to be undertaken using realistic fully coupled models that are validated against prior experiments. When applied to the re-qualification and life extension of FPU moorings, particularly with regard to re-qualification and life extension of in-place moorings, reliability analysis offers considerable advantages over conventional deterministic return period design. This paper details the application of a reliability approach to re-qualification and life extension of a turret-moored FPU that had design met-ocean conditions increased significantly over the life of the field. It explores key elements of reliability analysis including the probabilistic characterisation of met-ocean conditions, adequate representation of vessel dynamics and mooring loads in a Response Surface Model, and a selection of algorithms to solve for the system probability of failure. Discussion points include the advantages of the explicit identification of the most likely failure scenario versus uncertainty as to whether the worst design case has been identified, and the potential for rapid reassessment of reliability for specific design conditions (such as a degraded mooring system or a system for which degradation is ongoing). The results of this study demonstrate the significant advantages to the industry conferred by adopting reliability methods in the re-certification and life extension of existing FPU moorings. In particular, the study highlights that conventional mooring code deterministic design methods, whilst adequate for original design purposes, lack sufficient fidelity to address the multi-faceted issue of re-assessment of notionally marginal legacy systems. For a degraded existing mooring, an application of these methods can demonstrate that the level of reliability of the system is still acceptable, whereas a conventional approach may produce an over-conservative indication that the mooring is non-compliant. Applicable to a wide range of FPUs requiring re-qualification or life extension, the techniques discussed also provide pointers to more efficient and reliable mooring design for not just existing, but also for new FPUs.
Flow-Induced Vibrations of Riser Array System
Authors: Joshi Vaibhav , Liu Bin , Jaiman Rajeev K.
Published: October 2016

When a riser array system is subjected to a uniform flow, an unstable flow-induced vibration commonly occurs among cylinders, generally called fluid-elastic instability. It can cause long-term or short-term damage to the riser array system. A numerical investigation has been performed in the present study. Generally, flow-induced vibrations include vortex-induced vibration (VIV), wake-induced vibration (WIV), jet switching, turbulent buffeting and fluid-elastic instability. The dynamic interactions among the fluid-induced vibrations, wake interference and proximity interference pose difficulties in the design and operation of the riser array system. The dynamics of a riser array system is very different from that of basic canonical configurations such as side-by-side, tandem and staggered arrangements. In a riser array system, the interferences come from all possible nearby constituent risers. There is a synchronization phenomenon among the cylinders, which may lead to detrimental collisions and short-term failures. It is known that the vortex-induced vibration (VIV) of an isolated circular cylinder is self-limiting. An extensive vibration occurs in the lock-in region within which the frequency of the vortex shedding matches the structural frequency of the immersed structure. In a riser array system, there is a point at which the vibration of cylinder suddenly increases. The vibration of the constituent risers increases without bound with the increment of the free-stream velocity. This free-stream velocity is defined as the critical velocity. The interference not only comes from the inline and cross-flow directions, but also the wake interference from the diagonal upstream risers. In a riser array system, each riser vibrates independently. However, there is symmetry of frequency spectrum observed about the inline direction along the middle row of the risers.

In this study, the dynamic response of the different risers in the array system is investigated with the help of the amplitude response results from the canonical arrangements (side-by-side and tandem) and wake flow structures. The long top-tensioned riser system can be idealized by two-dimensional elastically mounted cylinders to solve the complex fluid-structure interaction problem. The dynamic response of a typical riser array system has been analyzed at low and high Reynolds number. It is encouraging to see that the results reported in the present investigation can provide useful insight and suggestions in the design and optimization of riser systems to avoid collisions and various long-or short-term failures.
Experiments and Hydrodynamic Analysis of an Adaptive Arresting Net Device for Protecting Bridge Piers Against Ship Collisions
Authors: Wang Y. G. , Wang B. Q. , Yang L. M. , Liu J. , Dong X. L. , Zhou F. H.
Published: October 2016

As the accident of a vessel impacting a bridge pier will result in serious disaster, such as bridge fall, ship sink and polluting environment, the technology and method have been investigated to prevent and protect bridges from vessel collisions. An adaptive arresting net crashworthy device has been developed for protecting non-navigable channel piers against ship collisions, which consists of mooring floating boats, mooring cable and mooring anchors, adaptive floating buckets, arresting net, triggering wire rope and constant resistant force cables. When a ship impacts the adaptive arresting net crashworthy device, first the head of the adaptive floating buckets will rise due to the floating force, then the arresting net fixed on the adaptive floating buckets captures and stops the ship. Enormous kinetic energy is consumed by a series of resistant force cables failure. The present paper presents the ship collision tests at full scale and hydrodynamic analysis of the adaptive arresting net crashworthy device. The ship collision tests has been conducted 6 times by a 1200DWT ship with different speed. The ship are prevented successfully. By using multi-body dynamics and rope dynamic theory, simulation model of the adaptive arresting net crashworthy device is established by hydrodynamic analysis software ANSYS-AQWA. It is found that the numerical simulation results are in reasonable agreement with the experimental results.
An Autonomous Robotic Platform for Detecting, Monitoring and Tracking of Oil Spill on Water Surface
Authors: Rathour Swarn Singh , Kato Naomi , Senga H. , Tanabe N. , Yoshie M. , Tanaka T.
Published: October 2016

With the aim of aiding mitigation efforts, in mapping and simulating the transport of the discharged hydrocarbon this paper proposes an autonomous surface vehicle (ASV), propelled by wind and water currents for the long-term monitoring of spilled oil on the ocean surface. This paper makes a unique contribution to the literature in proposing a cluster-based decision-making algorithm for sailing the ASV based on a complete scanning history of the area surrounding the vehicle by the oil detection sensor. A Gaussian-based oil cluster filtering algorithm is introduced to identify the largest oil slick patch. The physical constraints of the ASV have been taken in account to allow for the computation of feasible maneuvering headings for sailing to avoid sailing upwind (i.e., in the direction from which the wind is coming). Finally, using neoprene sheets to simulate oil spills, field test experiments are described to validate the operation of the ASV with respect to oil spill tracking using a guidance, navigation, and control system based on onboard sensor data for tracking the artificial oil targets.
A Preliminary Investigation on the Risk Arising From the Use of HP FGS System in LNGC by Analyzing Risk Contributors Comparatively
Authors: Yoon Joon Young , Park Sung-In , Lee Jae Bong , Kwon Seungmin , Hwang Yoonsik
Published: October 2016

This work is motivated by the need to identify the fire and explosion risk on LNGCs developed by Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME) because the main engines are designed to use highly pressurized natural gas (about 300 bar), which has caused vague fears of fire and explosion risks.

In this context, to identify the risk of fires and explosions quantitatively caused by ignitions of unintended leaked gas from fuel gas lines, a FERA was carried out for the LNGCs [1]. This paper, as a part of the FERA, presents the results of a preliminary investigation on the effect of introducing the highly pressured fuel gas system into LNGCs on the fire and explosion risk especially in the cargo compressor room. This study is conducted in a comparative way considering the risk contribution of each parameter that could impact on the fire and explosion risk in LNGCs. The effect of the highly pressured fuel gas is indirectly taken into account by the change of the initial leak rate in the system. To identify effects of the considered parameters quantitatively, dozens of simulations for the selected gas dispersion, explosion and fire scenarios were carried out using FLACS and KFX. Based on the results from the simulations, it is concluded that, in case of the LNGCs, the effects of the initial large leak rate due to the high pressure in the fuel gas pipes on fire and explosion risk are not significant compared with the other parameters’ effects.
A System for Measuring Ice-Induced Accelerations and Identifying Ice Actions on the CCGS Amundsen and a Swedish Atle-Class Icebreaker
Authors: Heyn Hans-Martin , Skjetne Roger
Published: October 2016

When ships operate in the Arctic, sea-ice induce an additional environmental load on the vessel. The ice load can vary significantly depending on the dominating ice-breaking failure mode.

In this work a sensor system for measuring ice induced accelerations on the Canadian icebreaker CCGS Amundsen and a Swedish Atle-class icebreaker is presented. The sensor system consists of low-cost inertial measurement units. Ship-ice interaction data has been collected during expeditions along the coast of Labrador in Canada and in the Greenland Sea north of the Norwegian Svalbard archipelago. Depending on the failure mechanism of the interacting ice, vibrations at different frequencies are induced into the icebreaker ship. A time-frequency decomposition based on the Wigner-Ville distribution has been modified such that it is applicable to analysis of ice-load induced acceleration signals. Based on the frequency pattern of the induced vibrations, this novel method allows for evaluation of the intensity of the ice-loads and identification of the dominating ice failure mechanism, which is demonstrated for several ship-ice interaction events.

The presented novel time-frequency decomposition for ice induced accelerations is a powerful tool for the identification of the threat imposed by sea-ice to a structure. In further work the time-frequency decomposition will be used as feedback in ice-capable control and monitoring systems for Arctic offshore operations.
Examination of Hydrodynamic Forces Acting on a Group of Circular Cylinders at High Reynolds Numbers
Authors: Shen Linwei , Jaiman Rajeev Kumar , Adaikalaraj Peter Francis Bernad , Joshi Vaibhav , Wang Jungao , Tan Sue Ben
Published: October 2016

A group of circular cylinders exists in many engineering practices, such as offshore drilling riser system. Due to the interference between the riser main tube and auxiliary lines, the hydrodynamic forces acting on the riser system is much different from those on a single circular cylinder. It is very rare in the publication and still not certain in the determination of the forces in the drilling riser design of the industry. Particularly, it is unclear of the hydrodynamic forces when the Reynolds number is very high which is quite common in the real ocean fields. In this paper, the stationary riser system consisting of a group of six circular cylinders with unequal diameters is considered. The hydrodynamic forces acting on the main cylinder in the Reynolds number ranging from 105 to 2×106 are numerically calculated by solving the Reynolds averaged Navier-Stokes (RANS) equations. The Spalart-Allmaras RANS model is employed to account for the turbulence effect. It is found that drag coefficients are close to 1 when the incoming flow is symmetrical with respect to the configuration of the cylinders and are dramatically reduced when the incoming flow is asymmetrical. No “drag crisis”, which is a well-known phenomenon in a single cylinder case, is found in this particular range of Reynolds numbers. A detailed analysis, including the flow field and pressure distribution around the main tube, is also presented in the present work. The numerical result of the hydrodynamic forces on the main line is very helpful for the engineers to determine the drag coefficients in the practice of drilling riser system design, under the guidance of API-RP-16Q.
The Relationship Between the Shape of Freak Waves and Nonlinear Wave Interactions
Authors: Fujimoto Wataru , Waseda Takuji
Published: October 2016

The local shapes of freak waves are essential to estimate responses of ships or offshore structures by freak waves for limit state design or maritime accident survey. It is known that freak waves deform like a crescent and their trough depth become asymmetric in directional and irregular wave fields. Meanwhile, Class I & II instabilities also affect wave shape.

We discussed how those instabilities affect the geometry of freak waves, using Higher Order Spectrum Method (HOSM) which is a fast simulator of water wave. This paper investigated the relationship between Class I & II instabilities and the nonlinear order of HOSM to separate the effects of the different order nonlinear instabilities on freak waves. This investigation and freak wave simulations by HOSM clarified that four-wave Class I instability with finite width wave spectra affected both the crescent deformation and the asymmetry. The results showed that Class II instability effects to the freak wave shapes were not significant.