bluuebunny/crossref_metadata_2025 huggingface dataset:
Mooring Analysis of a NOMAD Buoy Through Field Testing and Numerical Simulation
Authors: Baker Joshua , Yim Solomon C. , Amon Ean , Moran Sean , Lettenmaier Terry , von Jouanne Annette
Published: September 2014

This study presents a mooring analysis of the Ocean Sentinel buoy, which is a mobile test platform for Wave Energy Converters (WECs). The Ocean Sentinel is owned and operated by the Northwest National Marine Renewable Energy Center (NNMREC) at Oregon State University (OSU). The study involved a field observation as well as numerical modeling. The Ocean Sentinel was deployed from 7/29/2013 – 10/04/2013 at the NNMREC North Energy Test Site, which is located between 2–3 nautical miles (3.7–5.6 km) offshore of Yaquina Head, north of Newport, OR. It was configured in a three-point mooring with load cells on each mooring line. Prior to deployment, the numerical model was used for design and testing of the Ocean Sentinel mooring system. After deployment, recorded environmental conditions were coupled with the model to simulate deployed conditions, and model predictions of tension in the mooring lines were compared with actual results.
Study on the Test Results of Cross-Flow Vortex-Induced Vibration of a Towed Circular Cylinder
Authors: Wu Wei-Wu , Miao Quan-Ming , Wang Yan-Xia
Published: September 2014

This paper gives a review on VIV experimental research. A detailed introduction of the experimental study on the cross-flow vortex-induced vibration of a towed circular cylinder in CSSRC’s towing tank is presented and classical VIV phenomena are explained and analyzed in this study. However, some results which are much different from those in the classical literatures in the past few decades are observed at the same time. For example, instead of reduced velocity Ur from 5 to 8, the “lock-in” region happened in the reduced velocity ranged from 10 to 14 in our tests, where the reduced velocity is calculated by the natural frequency. The non-dimensional frequency (oscillation frequency over natural frequency) of about 1.8 in the “lock-in” region is also different from that of 1.0 in the classical literatures. Interestingly, the author found that some of the results given by Moe and Wu (1990), Sarpkaya (1995), Govardhan and Williamson (2000), Pan zhiyuan (2005) and so on, reported the similar phenomenon. Since above listed papers have the same points of view, whether can we say that the results in this paper are possible for the case of low mass ratio. To conclude that, however, many questions need to be answered. In an effort to gain a better understanding of VIV phenomenon, this paper presents results of further analysis on the test cases and parameters.
Design Challenge of Rigid Riser-Spool Piece Against HTHP Induced Expansion in Pipe-in-Pipe Systems
Authors: Wang Facheng , Gao Ming , Wang Jun , Zhang Yigong , Jia Xu , Huang Jun
Published: September 2014

Developments of oil and gas reservoirs in Bohai Sea, South China Sea etc., are presently accelerated, to cope with the significant increase in energy demand from the mainland, China. In recent developments in Bohai Sea, fluid temperature and pressure have been found dramatically being increased up to 100 °C and 20 MPa respectively. The fact that High Temperature and High Pressure (HTHP) in Bohai area brings design challenges, especially to jacket risers and spool pieces. Pipe-in-Pipe (PIP) flowline systems have been widely employed in this region and are continuously being considered for further developments. This is due to its significant thermal insulation capacity to deal with the High Temperature and High Pressure (HTHP) issue. To cope with the challenges induced by HPHT and structural complexity of PIP, COTEC Offshore Engineering Solutions, together with its mother company, China Offshore Oil Engineering Company, have developed a approach by using ABAQUS and AutoPIPE. This paper describes the relevant experience obtained during one development in Bohai Sea, BZ34-2/4 project containing dozens of risers and spool pieces. Two main parts are presented. Firstly, a beam-element based expansion calculation model adopting ABAQUS has been developed to achieve accurate HPHT induced expansions. The structural behavior of PIP can be represented in the developed model, meanwhile with minimum increase in modeling complexity. Secondly, practical and extensive parametric studies have been carried on the riser and spool flexibility against HPHT induced expansions. Since Bohai Sea has been developed extensively, many risers are post-installed and the existing of restriction areas practically enlarges the difficulties of anchor clamp and spool arrangements. Key parameters of these arrangements, such as Z/L shape, the length between two bends, the combinations of bend angles, the length of protection pipe on the riser etc. have been comprehensively investigated. “Gold” rules for rigid riser accessories arrangements and spool piece layout have been suggested accordingly.
Wave Instability in Finite Depths
Authors: Babanin Alexander V. , Ewans Kevin
Published: September 2014

Waves in finite-depth and shallow water represent an important and challenging research topic, both from practical and academic perspective. Most of practical applications related to the ocean are conducted in coastal areas, but most of research attention has been dedicated to the surface waves in deep water. Shallow areas are effectively a different physical environment, where wave kinematics change, waves become steeper and consequently more nonlinear but less or non-dispersive, and as a result their nonlinear behaviors change dramatically, waves directly interact with the bottom, in a number of different ways, and most importantly release their energy and momentum through intensive and extensive breaking.

In the paper, modulational instability in finite depths will be discussed. This mechanism is regarded responsible for rogue waves, and hence extreme wave heights in deep water. Extreme wave heights are a key design criterion for the ocean industry, including shallow environments too. It is believed, however, that wave breaking rather than wave instabilities is the primary mechanism that controls the maximum possible wave height in depth-limited environments. Here, data of the LoWish JIP will be used in order to identify the criteria for transition from modulational instability being active in the deep-water environments to being suppressed in the shallow waters.
Hydrodynamic and Hydroacoustic Phenomena in the Propeller Wake-Rudder Interaction
Authors: Felli Mario , Grizzi Silvano , Falchi Massimo
Published: September 2014

The present paper describes the major mechanisms underlying the hydroacoustic and hydrodynamic perturbations in a rudder operating in the wake of a free running marine propeller. The study was based on a holistic approach which concerned time resolved visualizations and detailed flow measurements around the rudder as well as wall-pressure fluctuation measurements over the rudder surface, at different deflection angles.
Centre of Pressure of 6 Degree of Freedom Loads, Applied to Impact Measurements on a Propeller Blade
Authors: Brouwer Joris , Hagesteijn Gerco
Published: September 2014

Load measurements on various structures and objects are nowadays common in technical industries and research fields. The same applies to numerical computations where fluid forces are integrated over surfaces to come to resultant forces and moments. When forces and moments on a rigid body in 3D are considered, the total load is a 6 degree of freedom system. These are often denoted as the force in x-, y- and z-direction and the moments around the x-, y- and z-axis. A question that often arises in case of these 6 degree of freedom loads, is to find the position of the centre of pressure. This is the position with zero resulting moment when the loads are translated to it. In 2D this is straightforward. However for 3D systems there is no straightforward solution. Extending the mathematics from 2D to 3D one might find a system of equations with a determinant that is zero. Which means there is no solution or there are an infinite number of solutions.

Studying this system of equations, a very convenient alternative can be posed. This alternative solution has been applied to find the centre of pressure on a propeller blade originating from open water loads, artificial ice impacts and combined ventilation and cavitation impacts. These measurements are all performed at model scale using 5 or 6 degree of freedom load sensors. The alternative method proved to deliver meaningful results which are backed up by high speed video footage of the impacting events.
Simulating Pitching Blade With Free Vortex Model Coupled With Dynamic Stall Model for Conditions of Straight Bladed Vertical Axis Turbines
Authors: Dyachuk Eduard , Goude Anders , Berhnoff Hans
Published: September 2014

This study is on the straight bladed vertical axis turbines, which can be utilized for both wind and marine current energy. Vertical axis turbines have the potential of lower installation and maintenance cost. However, complex unsteady fluid mechanics of these turbines imposes significant challenges to the simulation tools. Dynamic stall is one of the phenomena associated with the unsteady conditions, and it is in the focus of the study. The dynamic stall effects are very important for vertical axis turbines, since they are usually passively controlled through the dynamic stall. A free vortex model is used to calculated unsteady attached flow, while the separated flow is handled by the dynamic stall model. This is compared to the model based solely on the Leishman-Beddoes algorithm. The results are assessed against the measured data on pitching airfoils. A comparison of force coefficients between the simulations and experiments is done at the conditions similar to the conditions of H-rotor type vertical axis turbines.
Development of a Time Domain Boundary Element Method for the Seakeeping Behavior of a Cruise Ship Under Combined Strong Wind and Extreme Irregular Beam Seas
Authors: Gkikas G. D. , van Walree F.
Published: September 2014

A computational method for the seakeeping behavior of a cruise ship at zero speed and under severe wind and oblique wave loads is presented. The proposed methodology is a time-domain panel method where the transient Green functions used for the estimation and implementation of the free surface effects on the vessel’s motions are estimated assuming constant low lateral speed, instead of the common practice zero speed influence functions.

For the evaluation of the overall hydrodynamic forces, the so called “blended approach” is followed in the sense that the induced hydrodynamic pressures due to the scattering and radiation phenomena are calculated over the linearized position of the body, ignoring any displacements with respect to its mean position, while the hydrostatic and non-linear Froude-Krylov forces are considered at the actual body location and taking into account the free surface elevation at each time step.

For the validation of the proposed methodology, heave and roll motions, the drift velocity as well as lateral accelerations of the vessel were investigated for two cases of severe beam seas combined with a constant strong wind load and the results were compared against experimental model tests. The model tests were performed to investigate the vessel’s behavior under extreme weather conditions.

The low lateral speed Green functions were estimated for a speed similar to the one that the vessel was expected to drift, an estimation based on the model tests, as well as for the case where the input speed corresponded to the half of the expected speed. Good agreement was presented for both cases, showing that accurate and computationally efficient numerical simulations of the vessel’s motions under severe wind and wave excitations can be obtained by using low lateral speed transient Green functions.
Analysis of Mooring Lines for Wave Energy Converters: A Comparison of De-Coupled and Coupled Simulation Procedures
Authors: Yang Shun-Han , Ringsberg Jonas W. , Johnson Erland
Published: September 2014

Mooring systems for wave energy converters (WEC) have to be designed to survive the cyclic loads and motions they are subjected to as a result of the wave load-WEC interaction and the motions of the WEC in the random elevation of the sea surface. The current study compares four simulation procedures for the analysis of fatigue of WEC moorings. The objective is to recommend the type of simulation procedure that can be used to make reliable fatigue design of WEC mooring systems at a reasonable computational effort. A cylindrical floating WEC with four spread mooring lines is chosen for case study. The mooring dynamics of the WEC is simulated using coupled and de-coupled approaches in the time domain. In total, four types of simulation procedures are compared using the commercial simulation software DNV DeepC and an in-house code MOODY. A parameter sensitivity analysis of environmental conditions, model and numerical parameters is presented. The results are compared with respect to fatigue damage calculated using a stress-based approach and the rainflow counting method. It is found that a de-coupled approach, using DNV DeepC to simulate the buoy’s motions and cable response, is recommended since (i) it gives reliable results in terms of motion and stress responses of the buoy, mooring lines and accumulated fatigue damage, (ii) it requires the least model preparation by the engineer and the computation time is reasonable.
Slamming Impacts of Hydrodynamically–Supported Craft
Authors: Ikeda Christine M. , Judge Carolyn Q.
Published: September 2014

High–speed planing boats are subject to repeated slamming impacts, which can cause structural damage and discomfort or injury to passengers. The goal of this research is to study the fundamental physics of the water-impact of high–speed planing hulls and to measure the slamming loads and resulting motions of the craft upon re–entry into the water after becoming partially airborne. A set of towed scale–model experiments was conducted in calm water, regular waves and irregular waves to capture a sequence of individual impact events. Pressure measurements were taken on the bottom of the hull using both point sensors (PCB Piezotronics) and a pressure mapping system (Tekscan). The pressure signals from the pressure pads (providing both spatial and temporal resolution) and the point–pressure measurements (high temporal resolution) will be presented for individual slam events, allowing a deterministic approach to investigating high–speed planing craft wave slamming.
An Experimental Study on Progressive and Dynamic Damage Stability Scenarios
Authors: Lorkowski Oliver , Dankowski Hendrik , Kluwe Florian
Published: September 2014

Current damage stability rules for ships are based on the evaluation of a ship’s residual stability in the final flooding stage. The consideration of the dynamic propagation of water within the inner subdivision as well as intermediate flooding stages and their influence on the resulting stability is very limited in the current damage stability regulations.

The investigation of accidents like the one of the Estonia or the European Gateway reveals that intermediate stages of flooding and the dynamic flooding sequence result in significant fluid shifting moments which have a major influence on the time-dependent stability of damaged ships. Consequently, the critical intermediate stages should be considered when evaluating designs with large cargo decks like RoRo vessels, RoPax vessels and car carriers. Also the safety of large passenger ships with respect to damage stability is affected by the aforementioned effects.

In this context a new numerical flooding simulation tool has been developed which allows an evaluation of a ship’s time-dependent damage stability including all intermediate stages of flooding. The simulation model is based on a quasi-static approach in the time domain with a hydraulic model for the fluxes to ease the computation and allow for fast and efficient evaluation within the early design stage of the vessel. This allows studying multiple damage scenarios within a short period.

For the further validation of this numerical simulation method a series of model tests has been particularly set up to analyse the time-dependent damage stability of a floating body. The test-body has been designed specifically to reflect the most typical internal subdivision layouts of ships affected by the effects mentioned above.

The experimental study covers a static model test series as well a dynamic one. The static model test series has been set up with the aim to analyse the progressive flooding of selected compartments in calm water. Within the dynamic model test series, the model is excited by a roll motion oscillator to evaluate the influence of the ship motion on the water propagation and the associated damage stability.

The model tests presented in this paper comprise side leaks in typical compartments which are used for a basic validation of the simulation toll and the measurement devices. Particular attention has been drawn on damage scenarios with critical intermediate flooding stages in consequence of restricted water propagation. The presented results enable a further validation of the numerical flooding simulation and give an insight view on the chosen experimental setup.
A Parametric Study of Low-Frequency Damping of Mooring System
Authors: Chen Minglu , Huang Shan , Baltrop Nigel , Chunyan Ji , Li Liangbi
Published: September 2014

Mooring line damping plays an important role to the body motion of moored floating platforms. Meanwhile, it can also make contributions to optimize the mooring line system. Accurate assessment of mooring line damping is thus an essential issue for offshore structure design. However, it is difficult to determine the mooring line damping based on theoretical methods. This study considers the parameters which have impact on mooring-induced damping. In the paper, applying Morison formula to calculate the drag and initial force on the mooring line, its dynamic response is computed in the time domain. The energy dissipation of the mooring line due to the viscosity was used to calculate mooring-induced damping. A mooring line is performed with low-frequency oscillation only, the low-frequency oscillation superimposed with regular and irregular wave-frequency motions. In addition, the influences of current velocity, mooring line pretension and different water depths are taken into account.
Oscillating Wave Surge Converters: Interactions in a Wave Farm
Authors: Sarkar Dripta , Renzi Emiliano , Dias Frederic
Published: September 2014

The hydrodynamic behaviour of a wave farm comprising of Oscillating Wave Surge Converters (OWSC) is investigated using a mathematical model based on linear potential flow theory. The developed method can analyse a large number of wave energy converters in arbitrary configurations with oblique wave incidence and considers the hydrodynamic interactions amongst all the devices. The highly efficient novel method is based on Greens Integral Equation formulation, yielding hypersingular integrals which are finally solved using Chebyshev polynomials of the second kind. Using the semi -analytical approach, some possible configurations of a wave farm are studied. In the case of an inline configuration of the OWSCs with normal wave incidence, the occurrence of a near resonant behaviour already observed for 3 flaps is confirmed. A strong wave focussing effect is observed in some special configurations comprising of a large number of such devices. In general, the flaps located on the front of the wave farm are found to exhibit an enhanced performance behaviour in average, due to the mutual interactions arising within the array. A special case of two back to back flaps, oscillating independently, is also analysed using the above approach.
Numerical Simulation of an Oscillating Cylinder in Cross-Flow at a Reynolds Number of 10,000: Forced and Free Oscillations
Authors: Nguyen Linh Tuan The , Temarel Pandeli
Published: September 2014

In the present work, numerical simulations of flow past a circular cylinder in uniform cross-flow are investigated for three different cases: (i) a stationary cylinder, (ii) forced oscillations of a cylinder and (iii) free oscillations of a cylinder. All three cases were studied using a 2D CFD RANS code, at a Reynolds number Re = 10,000. The method adopted here is based on the Finite Volume Method using the commercial CFD package Ansys Fluent 14 with appropriate turbulence models. Comparisons with available experimental and numerical data, for all cases investigated, show that the simulations capture essential features of the fluid-structure interaction. These comparisons include drag and lift coefficients, Strouhal number, pressure distribution, as well as amplitude of motion and frequency ratio.
North Sea Mooring Systems: How Reliable Are They?
Authors: Brindley Will , Comley Andrew P.
Published: September 2014

In recent years a number of high profile mooring failures have emphasised the high risk nature of this element of a floating structure. Semi-submersible Mobile Offshore Drilling Units (MODUs) operating in the harsh North Sea environment have experienced approximately 3 mooring failures every 2 years, based on an average population of 34 units. In recognition of the high mooring failure rates, the HSE has introduced recommendations for more stringent mooring strength requirements for units operating on the UK Continental Shelf (UKCS) [17]. Although strength requirements are useful to assess the suitability of a mooring design, they do not provide an insight into the question: what is the reliability of the mooring system?

This paper aims to answer this question by evaluating failure statistics over the most recent decade of available data. Mooring failure rates are compared between the Norwegian Continental Shelf (NCS), the UKCS, and with industry code targets to understand how overall reliability is related to the strength capacity of a mooring system.

The failure statistics suggest that a typical MODU operating in the UKCS would experience a mooring line failure in heavy weather approximately every 20 operating years. This failure rate appears to be several orders of magnitude greater than industry targets used to calibrate mooring codes. Despite the increased strength requirements for the NCS, failure rates do not appear to be lower than the UKCS. This suggests that reliability does not correlate well with mooring system strength. As a result, designing to meet the more rigorous HSE requirements, which would require extensive upgrades to existing units, may not significantly increase mooring system reliability. This conclusion needs to be supported with further investigation of failure statistics in both the UKCS and NCS. In general, work remains to find practical ways to further understand past failures and so improve overall reliability.
Offshore Deployment of Point Absorbing Wave Energy Converters With a Direct Driven Linear Generator Power Take-Off at the Lysekil Test Site
Authors: Chatzigiannakou Maria A. , Dolguntseva Irina , Leijon Mats
Published: September 2014

Within the year 2013, four linear generators with point absorber buoy systems were deployed in the Lysekil test site. Until now, deployments of these point absorbing wave energy converters have been expensive, time consuming, complicated and raised safety issues. In the present paper, we focus on the analysis and optimization of the offshore deployment process of wave energy converters with a linear generator power take-off which has been constructed by Uppsala University. To address the crucial issues regarding the deployment difficulties, case study of previous offshore deployments at the Lysekil test site are presented regarding such parameters as safety, cost and time efficiency. It was discovered that the deployment process can be improved significantly, mainly by using new technologies, e.g., new specialized deployment vessels, underwater robots for inspections and for connecting cables and an automatized pressurizing process. Addressing the main deployment difficulties and constrains leads us to discovery of methods that makes offshore deployments more cost-efficient and faster, in a safety context.
Comparison of Second-Order Loads on a Semisubmersible Floating Wind Turbine
Authors: Gueydon Sébastien , Duarte Tiago , Jonkman Jason
Published: September 2014

As offshore wind projects move to deeper waters, floating platforms become the most feasible solution for supporting the turbines. The oil and gas industry has gained experience with floating platforms that can be applied to offshore wind projects. This paper focuses on the analysis of second-order wave loading on semisubmersible platforms. Semisubmersibles, which are being chosen for different floating offshore wind concepts, are particularly prone to slow-drift motions. The slack catenary moorings usually result in large natural periods for surge and sway motions (more than 100 s), which are in the range of the second-order difference-frequency excitation force.

Modeling these complex structures requires coupled design codes. Codes have been developed that include turbine aerodynamics, hydrodynamic forces on the platform, restoring forces from the mooring lines, flexibility of the turbine, and the influence of the turbine control system. In this paper two different codes are employed: FAST, which was developed by the National Renewable Energy Laboratory, and aNySIM, which was developed by the Maritime Research Institute Netherlands. The hydrodynamic loads are based on potential-flow theory, up to the second order. Hydrodynamic coefficients for wave excitation, radiation, and hydrostatic forces are obtained with two different panel codes, WAMIT (developed by the Massachusetts Institute of Technology) and DIFFRAC (developed by MARIN).

The semisubmersible platform, developed for the International Energy Agency Wind Task 30 Offshore Code Comparison Collaboration Continuation project is used as a reference platform. Irregular waves are used to compare the behavior of this platform under slow-drift excitation loads. The results from this paper highlight the effects of these loads on semisubmersible-type platforms, which represent a promising solution for the commercial development of the offshore deepwater wind resource.
Challenges and Developments in Navigational Risk Assessment With Large Uncertainty
Authors: Yan Xinping , Zhang Jinfen , Zhang Di , Guedes Soares Carlos
Published: September 2014

Concerns have been raised to navigational safety worldwide because of the increasing throughput and the passing ships during the past decades while maritime accidents such as collisions, groundings, overturns, oil-spills and fires have occurred, causing serious consequences. Formal Safety Assessment (FSA) has been acknowledged to be a framework widely used in maritime risk assessment. Under this framework, this paper discusses certain existing challenges when an effective safety assessment is carried out under a variety of uncertainties. Some theories and methodologies are proposed to overcome the present challenges, e.g., Fault/Event Tree Analysis (FTA/ETA), Evidential Reasoning (ER), Bayesian Belief Network (BBN) and Belief Rule Base (BRB). Subsequently, three typical case studies that have been carried out in the Yangtze River are introduced to illustrate the general application of those approaches. These examples aim to demonstrate how advanced methodologies can facilitate navigational risk assessment under high uncertainties.
Vortex Induced Motion of TLP With Consideration of Appurtenances
Authors: Tan Jaime Hui Choo , Teng Yih Jeng , Magee Allan , Ly Benedict Toong Heng , Bhat Aramanadka Shankar
Published: September 2014

Offshore floating platform configurations often consist of geometrically simple and symmetrical shapes which are made complicated by the presence of appurtenances such as helical strakes, tendon porches, steel catenary riser (SCR) porches, pipes, chains, fairleads and anodes on the surface of the hull. Previous studies mainly on spars show that these hull external features affect the Vortex Induced Motion (VIM) performance of the platform significantly. This is to be expected since VIM is controlled by the flow separation on the hull surface and the resulting vortex shedding patterns. Scale effects may also play a role in model tests for bare cylinders or hulls with bare cylindrical columns, whereas previous studies have shown less Reynolds dependence when appurtenances are modelled.

This study investigates the effect of hull appurtenances on VIM of a multi-column floating platform, i.e. a Tension Leg Platform (TLP) designed for Southeast Asian environment. Significant difference in VIM behaviors is expected between spars and TLPs since the column aspect ratios are very different and TLPs do not have helical strakes that are commonly fitted on spars. Model testing and Computational Fluid Dynamics (CFD) simulation are used in this VIM study, with the former being the emphasis of this paper. Descriptions of the respective experimental and numerical methodologies are presented and the comparison of the results is made. Further work required to improve the model test set-up and the CFD simulation are suggested. From this study, it is shown that the effect of appurtenances on TLP VIM simulation is important and must be taken into account to obtain realistic results.
Transportation Risk Analysis Framework for Arctic Waters
Authors: Khan Faisal , Yang Ming , Veitch Brian , Ehlers Soren , Chai Shuhong
Published: September 2014

Arctic waters have historically been relatively inaccessible for marine transport. Lately, climate change has made more of this region ice-free in the summer season. This has reduced the difficulty of marine transport in Arctic waters. Further, exploration and development of natural resources is increasing in Arctic regions, as is destinational shipping. The unique risk factors of this region, such as extremely low temperature, ice conditions and drifting icebergs, continue to pose threats to transportation. Potential impacts associated with marine transportation accidents warrant contingency plans that recognize that preventative measures may fail. To plan effectively, a transportation accident risk assessment model for Arctic waters is helpful. There is limited work on the development of such models. A new cause-consequences based risk assessment model is proposed here. The model estimates the probability of a transportation accident and also the related consequences during navigation in Arctic waters. To illustrate the application of the methodology, it is applied to a case of an oil-tanker collision on the Northern Sea Route.
Study on the Sloshing Load of FLNG
Authors: Zhu Xiaosong , Xie Bin , Yu Xichong , Du Qinggui
Published: September 2014

As one of the most promising equipment for deep far sea gas field development, FLNG has been widespread concern in the engineering sector. Due to the characteristic of LNG, the sloshing of liquid tank in FLNG is inevitable. Therefore, the sloshing load of liquid tank is one of the hotspots in engineering and academic research. In this paper, in order to simulate the sloshing load of liquid tank in FLNG, a secondary development software is proposed based on the commercial software FLUENT. The simulation results agree well with previous experimental results. This shows the accuracy of the simulation of the software. In addition, the longitudinal and transverse section of LNG tank is analyzed. The results shows that different excitation frequencies and amplitudes great influence on the sloshing load of liquid tanks, different filling levels also have a certain influence. This will be used to estimate the size of sloshing load for the FLNG equipment which may encounter in the real sea condition, and have certain significance in practical engineering.
A New Approach to Determine Cutting Forces in Brittle Rock Under Hyperbaric Conditions
Authors: Miedema Sape A.
Published: September 2014

Merchant (1944), (1945A) and (1945B) derived a model for determining the cutting forces when machining steel. The model was based on elastic-plastic deformation and a continuous chip formation (ductile cutting). The model included internal and external friction and shear strength, but no adhesion, gravity, inertia and pore pressures. Later Miedema (1987 September) extended this model with adhesion, gravity, inertial forces and pore water pressures. These models however only describe the so called Flow Type of cutting process, which is the ductile cutting process. The ductile cutting process requires a relatively large tensile strength (BTS) compared to the compressive strength (UCS) or shear strength. If the tensile strength is not large enough, brittle failure based on tensile failure may occur. This paper describes a new method of determining the cutting forces resulting from brittle failure, still based on the original ductile models, but with a correction for the stresses. This new model can be used for Deep Sea Mining Applications. It is assumed that materials which behave brittle under atmospheric conditions will behave ductile under hyperbaric conditions.
Safety of LNG Transportation in Arctic Conditions When Using Systems of Various Types
Authors: Shaposhnikov Valery M. , Nesterov Alexander B. , Aleksandrov Anatoly V. , Vasilik Evgeniia G.
Published: September 2014

Possible expansion of the LNG sea transportation region to the Russian Arctic makes topical the issue on feasibility of using various types of cargo containment systems for large ice LNG carriers of higher ice class notations.

When analyzing safety of LNG transportation in the Arctic conditions in case of using cargo containment systems of various types, both fatigue issues adjusted for ice effects (this is especially topically for membrane containment systems) and consequences of emergency situations shall be studied.

To evaluate fatigue of membrane cargo containment systems, a special finite element analysis was performed; at that ice effects on the hull were considered together with vibration caused by screws and engines for the purpose of determining maximum possible excitations occurring during the ice navigation. Static, dynamic and life tests, that permitted to estimate experimentally the fatigue margin of membrane containment system elements’ attachment to the vessel hull, were conducted as well.. The study results permit to conclude that the fatigue of CCS NO96 membrane cargo containment system is quite sufficient for resisting vibration loads, which occur during 40-year service life of large Arctic LNG carriers in severe ice conditions.

Another important aspect of LNG transportation safety in Arctic conditions consists in accidental load problems. The following types of emergency situations were considered:

• accident collision of vessels (LNG carrier ramming by another vessel);

• landing on rock (bottom collision with rock in sea conditions);

• hull side impact against an iceberg fragment during turning.

Consequences of vessels’ collision and impacts against an iceberg were evaluated with the use of software LS-DYNA. It was ascertained based on the performed analysis that the feasibility of LNG carriers with membrane containment systems is minimal; the feasibility of LNG carriers with SPB containment systems is slightly higher, and the feasibility of LNG carriers with MOSS containment systems is essentially higher than that of LNG carriers with membrane containment systems. It could be explained physically by the fact that MOSS cargo containers approach the outer shell plating near the centerline plane (for the bottom) and in the compartment middle (for the side and bottom) only; when moving off from the centerline plane and the compartment middle the distance between cargo containers and the outer shell plating essentially grows.

Nevertheless, development of large Arctic LNG carriers having sufficient accidental load levels is possible on application of any containment system type.
Prediction of Mooring Line Tensions for Hurricane Conditions in the Gulf of Mexico
Authors: Mathisen Jan , Hørte Torfinn
Published: September 2014

A probabilistic metocean model for hurricane conditions is briefly described. The model is based on site-specific, hindcast data and defines the time variation of the metocean conditions during the realisation of a hurricane at the site. The annual extreme value distribution of mooring line tension for a large, semi-submersible, mobile drilling unit is computed. Time domain analysis is applied to obtain the short-term, extreme value distribution of line tension, conditional on stationary metocean conditions. A large number of different conditions are considered. A response surface is used to interpolate on the short-term distribution parameters in order to describe the tension response during the varying conditions associated with the passage of a hurricane. The hurricane duration is split into a sequence of 15-minute intervals such that the conditions can be assumed stationary during each such short interval. The tension distribution, conditional on the realisation of a hurricane, is accumulated across the sequence of short intervals. The distribution of hurricanes is taken into account to obtain the tension distribution in a random hurricane. Finally, the frequency of hurricanes is taken into account to give the annual extreme distribution of line tension. The characteristic tension computed using 10-year return conditions and the ISO 19901-7 design standard is found to correspond to a return period of 29 years in the test case. The effects of various assumptions in the design analysis are investigated. Sensitivities to simplifications of the metocean model are considered. The effects of uncertainties in the response calculation and in the distribution of peak significant wave height during hurricanes are quantified and included in the response analysis.
Interaction Between Warm Model Ice and a Propeller
Authors: Huisman T. J. , Bos R. W. , Brouwer J. , Hagesteijn G. , de Koning Gans H. J.
Published: September 2014

Ships sailing in ice require a propeller that is able to endure both extreme loads and fatigue loads and operate efficiently in ice and open water. Knowledge and descriptions of the physical processes of propeller-ice interaction are essential to model the interaction with its dominant parameters and finally predict the loads. The research described in this paper uses an experimental setup to determine if the crushing strength of ice, or in general a solid, is a dominant parameter in propeller-ice interaction as stated in empirical and theoretical models. Warm model ice, a paraffin based material to be used at room temperature, with ex-situ tested crushing strength, density and elasticity, is supplied to an in-situ model propeller at different rpms. One blade of the propeller is equipped with a six-component load sensor. Impacts are recorded in the time domain and synchronised with high speed footage. The data is analysed to understand and explain the impact behaviour by comparing it with rotational speed, load and footage. Scaling of the warm model ice properties is discussed as well due to density differences between warm model ice and sea ice.
Fatigue Evaluation Procedures for Multiaxial Loading in Welded Structures Using Battelle Structural Stress Approach
Authors: Hong Jeong K. , Forte Thomas P.
Published: September 2014

The Battelle structural stress method is examined for the evaluation of multiaxial loading fatigue behavior in welded structures. Even though the structural stress and its master S-N curve approach have been mainly focused on normal loading dominant (Mode I) failure cases, the evaluations on multiaxial loading weld fatigue using structural stress parameters have been relatively recently performed such as using the modified Gough ellipse [1] and the path-dependent maximum range (PDMR) cycle counting procedure [2].

In this article, in order to evaluate the multiaxial fatigue behavior, an effective equivalent structural stress range (EESS) parameter is defined as a von Mises form of combined normal and in-plane shear equivalent structural stress ranges. The newly developed in-plane shear equivalent structural stress range for in-plane shear dominant loading (Mode III) is introduced. This in-plane shear equivalent structural stress range parameter has been formulated based on the evaluation of fatigue behavior under in-plane shear loading. Also, the EESS parameter is a function of damage parameter based on the PDMR procedure.

In this article, the procedure employing the EESS parameter is evaluated and validated using published weld fatigue data. The multiaxial fatigue date is consolidated within a small scatter band regardless of in-phase, out-of-phase, and non-proportional loading as well as torsional loading. Finally, the design master S-N curve is proposed for multiaxial loading weld fatigue.

It is found that the dimensionless bend ratio parameter, Iτ (rτ)1/mτ for in-plane shear loading is a much more significant correction than that for normal loading when the ratio of bending structural stress to the total structural stress, rτ increases. This procedure will be beneficial for fatigue design with preventing over-conservatism.
Analytical Prediction of Progressive Structural Failure of a Damaged Ship for Rapid Response Damage Assessment
Authors: Bardetsky Alexander , Lee AiKuo
Published: September 2014

The assessment of the residual strength of a damaged ship is a key element of ABS’ Rapid Response Damage Assessment (RRDA) program. When determining the residual strength, it is important to understand how the initial structural damage can spread in response to sea wave dynamic loads and can lead to a gradual reduction of the ship’s residual strength. This progressive, time-dependent structural failure caused by cracks emanating from the damaged area could eventually lead to total hull girder collapse. This is why it is important to quantify the progressive structural failure over time when assessing the residual strength of the damaged ship. Until now, progressive structural failure analysis has been conducted numerically using the Finite Element (FE) modeling approach. While this approach is accurate, it is extremely time-consuming, which makes it inappropriate for incident response, where time for decision-making is very limited. In order to overcome this limitation, an alternative analytical modeling approach for assessing the progressive structural failure of a damaged ship is proposed.

This paper presents a new comprehensive procedure for analytical prediction of crack propagation under sea wave loading using spectral fatigue analysis, beam theory, fracture mechanics and an equivalent stress intensity factor (SIF) range concept. The SIF range obtained analytically is validated by FE modeling of a damaged ship subjected to sea wave dynamic loading. The procedure for analytical prediction of the crack propagation is demonstrated for a typical, modern 170,000 DWT bulk carrier in a full load condition. The results of this research can be used to support informed decision-making when analyzing a vessel’s residual strength for the transit voyage from the accident location to a repair facility.
Analysis of U-Type Anti-Roll Tank Using URANS: Sensitivity and Validation
Authors: Kerkvliet Maarten , Vaz Guilherme , Carette Nicolas , Gunsing Michiel
Published: September 2014

The roll motion of ships operating in a seaway is often limiting operations. These limits could be due to, e.g. maximum acceleration, green water, capsize risk or just comfort. Therefore additional roll damping is desired to prevent uncontrolled roll motion. Different means are available to decrease the roll motion of a ship, amongst other these include bilge keels, active fin stabilizers (either for forward or zero speed) and U-shape or free surface anti-roll tanks (ART). The amplitude and phase of the roll opposing moment resulting from the water that moves inside the ART are a function of the geometry of the tank and especially its internal damping. Due to the complex and non-linear nature of this flow, the use of Computational Fluid Dynamics (CFD) was chosen to analyse the details of the flow inside the tank and its anti-roll performance. The present paper focuses on the sensitivity and validation of the anti-roll performances of passive U-type ART using CFD. For this, the incompressible Unsteady Reynolds Averaged Navier-Stokes (URANS) code ReFRESCO was used. The sensitivity on the results for the U-tank is analysed by varying the grid resolution and the numerical time step. The two-dimensional (2D) full-scale and Froude based model-scale ReFRESCO results are compared to 2D and 3D full-scale CFD results of Delaunay (2012) [1] and Thanyamanta and Molyneux (2012) [2] and validated with model-scale experimental results of Field and Martin (1975) [3] and MARIN experimental results by Gunsing et al. (2014) [4]. This paper shows the influence of the convective scheme for capturing the free-surface interface and provides recommendations for a time step and grid resolution to effectively calculate the roll damping of an ART.
Acoustic Reflectometry for Blockage Detection in Pipeline
Authors: Loureiro Silva L. , Monteiro P. C. C. , Vidal J. L. A. , Netto Theodoro A.
Published: September 2014

Flow assurance is an important aspect of offshore, particularly deepwater pipeline design and operation, since one of the critical issues is the eventual initiation and growth of hydrate or paraffin blockages under certain conditions. Ideally, operators would benefit from online information regarding position and extent of an eventual blockage in a pipeline. The aim of this work is to apply acoustic technology to design and make a prototype that can be used in a pipe to efficiently identify and measure blockages. The technique uses a short duration sound pulse that is injected into the pipe. When the acoustic pulse encounters an impedance discontinuity, a portion is reflected back towards the acoustic source and microphones or hydrophones. Analysis of the measured signal reflections can provide valuable data related to location and size of the blockages. An experimental setup with a pipe of 4″ internal diameter and length of 100 m was constructed, and different excitation signals for the impulsive response function measurements were conducted. Microphones and hydrophones measurements were recorded using a fit-for-purpose data acquisition system with sampling rates of up to 1kS/s per channel. The tests were performed in air and water using different sizes of blockages and in different positions in the pipe. In parallel, finite element analyses were performed using the commercial software Abaqus to simulate the same conditions. The experiments were numerically reproduced with good correlation proving the potential of the technique.