bluuebunny/crossref_metadata_2025 huggingface dataset:
A Multi-Domain Approach in 3-D Diffraction Calculations
Authors: Pinkster J. A.
Published: November 2011

Prediction of the wave-induced motions of vessels moored in locations with complex bathymetry involving variable water depth represent a challenge for standard 3-dimensional diffraction methods. In this paper a modified diffraction method is introduced based on a multi-domain approach capable of handling different water depths in each domain. The theoretical background is briefly discussed along with some aspects of the numerical implementation. The method is applied to three examples which are known to present difficulties for the standard diffraction codes based on a single water depth and one involving infinitely long reflecting boundaries.
Shakedown Analysis of Offshore Platform Under Varied Combined Loading
Authors: Zhang Qiyi , Dong Sheng
Published: November 2011

Based on static Melan shakedown theorem, an elastic-plastic finite element method is presented to analyze the shakedown of saturated undrained foundation due to varied combined loadings, and the shakedown loadings under different patterns of loading combination are compared. At the same time, a comparison is given between the shakedown failure envelop under varied combined loading and the failure envelop of ultimate bearing capacity under static equilibrium, and it is found that the shakedown loading under varied combined loading is less than the ultimate bearing capacity under combined loading.
Mechanical Behaviour of Lined Pipe During Bending: Numerical and Experimental Results Compared
Authors: Hilberink A. , Gresnigt A. M. , Sluys L. J.
Published: November 2011

A promising possibility to reduce costs in pipelines that require corrosion resistant alloys (CRA) is the use of lined pipe, consisting of a carbon steel load-bearing outer pipe that provides the structural capacity and a corrosion-resistant alloy (CRA) liner, protecting the carbon steel outer pipe from the transported corrosive product. The objective of the current research is to identify all variables that have an influence on the mechanical behaviour of lined pipe during bending. The parameters that determine the resistance to pipe ovalisation and liner wrinkling have to be quantified, enabling safe and economic design of lined pipe for installation. In this paper, the influence of friction and mechanical bond on the behaviour of lined pipe during bending is investigated in three dimensional computational models. The numerical results are compared with the results of pure bending tests.
Assessment of Hydrocarbon Explosion and Fire Risks in Offshore Installations: Recent Advances and Future Trends
Authors: Paik Jeom Kee , Czujko Jerzy
Published: November 2011

This article presents a review of the state-of-the-art technologies used in assessing the risk of hydrocarbon explosions and fires in offshore installations. Both qualitative and quantitative risk assessment approaches are described, and the modelling techniques employed in the quantitative assessment of explosions and fires are presented. Procedures developed through a joint industry project on the explosion and fire engineering of floating, production, storage and offloading units (abbreviated hereafter as EFEF JIP) led by the authors are introduced. This article does not attempt to survey the literature, but rather to summarise recent advances and future trends in terms of the technological aspects of the risk assessment of offshore installations subject to explosions and fire.
Comparison of Sloshing Impacts for Rectangular and Chamfered LNG Tanks
Authors: Pistani Fabrizio , Thiagarajan Krish , Roddier Dominique , Finnigan Tim
Published: November 2011

One of the most utilised methods for the mitigation of impact forces due to the violent motions of LNG inside transported tanks is the chamfered geometry of the top corners. Nevertheless for some conditions the pressures may still reach a significant magnitude during the impacts of the fluid on the boundaries of the tank. Therefore there is the necessity to assess the magnitude of such pressure impacts, their numbers and also the location where those impacts are more likely to happen. In this study these issues will be addressed experimentally through comparison of data from two extensive measurement campaigns carried out with scaled models of different tank geometries across a number of different conditions. The number, position, magnitude and type of impacts in the most significant conditions for the two geometries are experimentally measured, assessed and compared. The comparison of the data shows that relevant impacts still occur in the case of a chamfered tank and that their magnitude, although reduced, is not negligible. In comparison with the rectangular tank there is one more location of high impacts because the fluid changes direction at the two corners of the tank. The most critical conditions are still for the medium/low filling levels, around 30%. For the higher filling levels, above 70%, the chamfered geometry is particularly effective, as it may be expected, in reducing the maximum pressures.
Assessment of Full-Scale Measurements With Regard to Extreme Hogging and Sagging Condition of Container Ships
Authors: Mao Wengang , Ringsberg Jonas W. , Li Zhiyuan , Rychlik Igor
Published: November 2011

In the design of a vessel’s ultimate strength the extreme hogging condition is of great concern. Due to special properties of container ship structures, such as large bow flare and overhanging stern, wave-induced slamming makes the ship responses more skewed to sagging conditions. In particular in large sea states, the ratio between maximum sagging and hogging can be quite high. Hence, the sagging condition might be very crucial with respect to a ship’s ultimate strength. In this study, the extreme response caused by hogging and sagging is derived from upcrossing spectrums of ship responses. The Weibull fitting method and Rice’s formula for the computation of the upcrossing spectrum are discussed using full-scale measurements from a container vessel on the North Atlantic trade. The extreme ship responses are therefore predicted using the long-term upcrossing spectrum. In the case where the ship response can be approximately treated as a series of stationary Gaussian processes, the corresponding upcrossings are computed by the explicit Rice’s formula. For the non-Gaussian ship response, it is shown that the 4-moment Hermite transformation is an efficient approach to compute the corresponding upcrossing spectrums. The parameters in the transformation mainly depend on the wave environments and operation profiles. The relations between these parameters and the wave environments are needed if no measurement is available. However, according to the full-scale measurements, it is not possible to find general formulas to estimate the parameters in terms of wave environments or operation profiles for the practical applications.
Estimation of the Shape Evolution and the Growth History of an Embedded Crack by Fatigue Loading
Authors: Gotoh Koji , Harada Keisuke , Anai Yosuke
Published: November 2011

Fatigue life estimation for planar cracks, e.g. part-through surface cracks or embedded cracks is very important because most of fatigue cracks found in welded built-up structures show planar crack morphologies. Fatigue crack growth behaviour of an embedded crack in welded joints is investigated in this study. The estimation procedure of crack shape evolution for an embedded crack is introduced and validation of the estimation procedure of fatigue crack growth based on the numerical simulation of fatigue crack growth with EDS concept for an embedded crack is performed. The validity of the proposed shape evolution estimation method and the fatigue crack growth simulation based on the fracture mechanics approach with EDS concept are confirmed.
Long-Term Distribution of the Extreme Values of Offshore Structural Response by Finite-Memory Nonlinear System Modelling
Authors: Mohd Zaki N. I. , Najafian G.
Published: November 2011

Offshore structures are exposed to random wave loading in the ocean environment and hence the long-term probability distribution of the extreme values of their response to wave loading is of great value in the design of these structures. Due to nonlinearity of the drag component of Morison wave loading and also due to intermittency of wave loading on members in the splash zone, the response is often non-Gaussian; therefore, simple techniques for derivation of the extreme response probability distributions are not available. However, it has recently been shown that the short-term response of an offshore structure exposed to Morison wave loading can be approximated by the response of an equivalent finite-memory nonlinear system (FMNS). In this paper, the approximate FMNS models are used to determine both the short-term and the long-term probability distribution of the response extreme values with great efficiency.
Conditional Risk Assessment Considering Hull Girder Failure of Vessels With Collision-Induced Damage Amidships
Authors: Jia Huirong , Moan Torgeir
Published: November 2011

This paper deals with conditional risk assessment considering hull girder failure of damaged vessels. Only damages amidships are investigated. Conditional risk in this paper is defined as the probability of a given damage multiplied by the probability of hull girder failure conditioned upon the given damage. Taking a double hull oil tanker at full load condition as an example, the 3-hour’s failure probabilities conditioned upon damage properties are estimated. The statistical database for collision event in the HARDER project is adopted to assess the probability of sea state and damage. The sensitivity of 3-hour’s failure probability to the sea state and damage properties is investigated. Furthermore, the conditional risk is also assessed.
Alleviation of Fatigue in Renewable Energy Support Structures
Authors: Brennan Feargal
Published: November 2011

Offshore renewable energy is experiencing an explosion of activity in response to ambitious renewable energy targets, however the drive to increase turbine size in deeper water whilst at the same time to reduce capex and installation costs in addition to the speed of development means there is a danger that structures may be designed and deployed that are inherently prone to fatigue. Offshore structures have come a long way since the pioneering early Oil & Gas jackets in the 1960s and 1970s. In forty years of designing and operating large Oil & Gas structures in the North Sea tremendous changes have occurred in development of advanced numerical modelling of stress, fatigue and loading in addition to vast improvements in steel quality/strength, manufacturing processes and inspection, monitoring and quality control. This paper addresses some of the fundamental areas where current design standards may not be appropriate for renewable energy support structures in this new era of advanced sensors and information systems. It will also discuss advanced fatigue alleviation techniques.
Secure Launch of Lifeboats in Cold Climate: Looking Into Requirements for Winterization
Authors: Torheim Steinar , Gudmestad Ove T.
Published: November 2011

In this paper we will look closer into the secure launching of lifeboats from the Diving Support Vessel (DSV) “Seven Havila” in cold climate. Further we will look into requirements for winterization of such equipment. An overview of the vessel, the davits and other launching equipment will be included and critical components in the system will be discussed, viewed in the light of secure launching and winterization. This paper will define some of the environmental challenges coming from meteorological conditions when operating in cold climate regions. In this respect, particular focus will be drawn to challenges related to Polar Low Pressures and icing. These are conditions relevant for the Norwegian Sea and Barents Sea where the vessel is likely to operate. The paper will then look into possible winterization measures that can have a positive effect when it comes to protecting the launching equipment against icing. The most challenging situation will be the spray ice coming from waves and wind and this will also have the highest focus. In addition to installed winterization measures, known ice removal measures/methods will be looked at. Finally a discussion will be presented based on the investigations and information produced. For the “Seven Havila” the most likely season for operation in arctic/cold climate areas will not be during wintertime. However, to be prepared for operations in cold climate, lifeboat launching equipment must be winterized for the physical environmental conditions it is exposed to. Evacuation equipment must at all times be functional and collecting data and performing thorough analysis of the operational conditions is essential to define the winterization requirements. The lifeboats and the launching equipment on the “Seven Havila” are already partly protected by their location in compartments. Additionally, the most effective way of preventing sea-spray and thereby also icing, will be by closing the compartments. Different kinds of removable covers may be considered. In the ship operation industry there is a need for amendments to the existing winterization guidelines and new “Guidelines for Ships Operating in Polar Waters” to define the requirements for such. For the life saving equipment in particular, the guidelines should include the temperature requirements for different operational seasons. It is, furthermore, important to have a close look at the training programme of personnel and the operational preparations and maintenance program for equipment to evaluate if improvements are required for operations in cold climate.
Extreme Wave Impact on Offshore Platforms and Coastal Constructions
Authors: Veldman Arthur E. P. , Luppes Roel , Bunnik Tim , Huijsmans Rene´ H. M. , Duz Bulent , Iwanowski Bogdan , Wemmenhove Rik , Borsboom Mart J. A. , Wellens Peter R. , van der Heiden Henri J. L. , van der Plas Peter
Published: November 2011

Hydrodynamic wave loading on structures plays an important role in areas such as coastal protection, harbor design and offshore constructions (FPSO’s, mooring), and there is a need for its prediction up to a detailed level (max./min. pressures, duration of pressure peaks, shear stresses, etc.). In close cooperation with industry, long-year joint-industry projects are carried out to develop a numerical simulation method: the CFD method ComFLOW. The two major application areas are the prediction of extreme wave forces on offshore platforms and offloading vessels, and the prediction of impact forces on coastal protection structures. The paper will present a short overview of the method, some recent results and future plans.
Three-Dimensional Effects for a Ship Experiencing Large Amplitude Roll Motion
Authors: Bassler Christopher C. , Miller Ronald W.
Published: November 2011

Recent advancements have been made to consider the effects of large amplitude motions for roll damping models used for numerical ship motion performance assessments. These advancements have been focused on the development and expansion of models for potential flow simulation tools with sectional formulations. However, additional 3D effects due to vortex shedding, flow convection downstream, waves, and bilge keel emergence and submergence during large roll motion may be important, but are typically neglected in the sectional formulations. A series of RANS computations were performed for both 2D and 3D conditions of large amplitude ship roll motion, with and without forward speed, and in calm water and in waves. Comparisons were made to available experimental data for the 2D calm water conditions at zero-speed. These results were then assessed with the 3D conditions to develop improved understanding of additional 3D effects, including forward speed and waves, which should be considered for future developments of strip-theory approaches for ship motions prediction.
Development of Hull Forms for a 190,000 DWT Icebreaking Ore Carrier
Authors: Park Kyung Duk , Chung Yong Kwan , Jang Young Sik , Kim Hyun Soo , Molyneux David
Published: November 2011

This paper describes the development of three candidate hull forms for 190,000 DWT ore carrier for operation in ice covered water. It builds on Hyundai Heavy Industries expertise in ore carrier design, and discusses some of the changes required for operation in heavy ice conditions. The overall concept was to have a target speed of 6 knots in land fast ice 1.7m thick and 15 knots in open water. Three candidate bow shapes were designed and analyzed, based on a common stern arrangement. The development of the hull form included three methods of predicting the performance of the ships in ice. Empirical analysis was carried out for all three hulls, based on experience gained from model experiments on bulk carrier hull forms in ice. Numerical analysis was carried out on all three bow shapes using a computer program (based on the discrete element method) to simulate the interaction between the ship and the ice. Physical model experiments were carried out for resistance and propulsion in level ice, pack ice and ridges on the selected design. As a result of the model experiments, the selected bow shape was modified to reduce its resistance in ice. The improved performance of the modified hull was confirmed with additional numerical simulations.
An Experimental Analysis of a Flexible Riser in Jumper Configuration
Authors: Murai Motohiko , Yamamoto Marcio , Uto Shotaro , Fujiwara Tomo
Published: November 2011

Nowadays, flexible risers are widely deployed in various configurations for the production of hydrocarbons in offshore fields. For example, in the self-standing hybrid risers’ applications, a single riser or a set of risers are suspended by a subsurface buoy called “Can”. Then a piece of flexible riser connects the Can to the production platform conveying the hydrocarbon production stream. This work concerns about this jumper, an experiment using a 10 m long model was carried out at the Deep Sea Basin of the National Maritime Research Institute in Japan. The model was made by three concentric unbonded layers: a silicon made inner layer; a crisscross steel wire layer; and a rubber made outer layer. During this experiment, the model was suspended through both ends; one model’s end was fixed and the other end was connected to an oscillator that generates the oscillatory motion in three different directions. In addition, a positive displacement pump injected fresh water into the model. Further, the model was instrumented with two degrees of freedom accelerometers fixed along its length; and a six degrees of freedom force/torque transducer was also installed at one pipe end. In addition, the Deep Sea Basin’s Visual Measurement System tracks and calculates the motion of several measurement stations along the pipe. A parametric analysis was carried out changing the oscillating frequency and internal flow rate. Discussion and results of numerical simulation are also included.
Identification of Ringing Events for a Slender Tubular Marine Structure
Authors: Iwanowski Bogdan , Astrup So̸ren , Lefranc Marc , Hansson Rolf
Published: November 2011

Marine structures can experience loads coming from steep, non-linear waves. A transient response of the structure can be amplified in some circumstances due to phenomenon known as “ringing”. Exact conditions of the ringing response excitation are not well known and various definitions of what constitutes a ringing event appear in bibliography. This article aims at identification of ringing events for a slender marine structure subjected to the second order nonlinear irregular waves. Loads on the structure are calculated from Morison equation with extensions known as Rainey’s slender body theory. Consistent second order formulation for the flow kinematics above mean water level is employed. The excitation load is non-linear due to wave non-linearity, Morison equation’s drag term and non-linear inertia terms which can be found in Rainey’s formulation. The structure’s dynamic response is obtained by Finite Element calculations in time domain. Overall randomly-excited vibrations are analysed by statistical and spectral methods, and application of Continuous Wavelet Transform (CWT) is presented. The simulations show a number of sudden, high amplitude resonant events which can be classified as ringing.
CFD for Multiphase Flow Transport in Pipelines
Authors: Ramdin M. , Henkes R. A. W. M.
Published: November 2011

There is an increasing interest in applying three-dimensional Computational Fluid Dynamics (CFD) for multiphase flow transport in pipelines, e.g. in the oil and gas industry. In this study the Volume of Fluid (VOF) multiphase model in the commercial CFD code FLUENT was used to benchmark the capabilities. Two basic flow structures, namely the Benjamin bubble and the Taylor bubble, are considered. These two structures are closely related to the slug flow regime, which is a common flow pattern encountered in multiphase transport pipelines. After non-dimensionalization, the scaled bubble velocity (Froude number) is only dependent on the Reynolds number and on the Eo¨tvo¨s number, which represent the effect of viscosity and surface tension, respectively. Simulations were made for a range of Reynolds numbers and Eo¨tvo¨s numbers (including the limits of vanishing viscosity and surface tension), and the results were compared with existing experiments and analytical expressions. Overall there is very good agreement. An exception is the simulation for the 2D Benjamin bubble at low Eo¨tvo¨s number (i.e. large surface tension effect) which deviates from the experiments, even at a refined numerical grid.
Measured and Analytical Studies of Dynamic Ocean Water Pressure Against a Vertical Caisson During a Real Earthquake
Authors: Ishibashi I. , Arablouei A.
Published: November 2011

The heavily instrumented full scale caisson (9 m high), constructed at the port of Kushiro (Kushiro, Hokkaido, Japan) in 2001, was impacted by a major earthquake hitting the site in September 2003 (M = 7.5 with the maximum acceleration of 143.5 gals) where the dynamic water pressures from both backfill and seawater side were recorded. While comparing the recorded dynamic water pressure with Westergaad’s theoretical solution [1], noticeable discrepancy was observed between compression phases of applied dynamic pressure on wall whereas an excellent correspondence was noticed in dynamic suction. In this paper, the soil-seawater-caisson system has also been numerically modeled using Finite Element Technique. The recorded data in terms of applied ocean water pressure on wall is analyzed and compared with numerical results as well as Westergard solution. The results demonstrate that, the recorded dynamic ocean water pressure was rather close to Westergard’s solution in suction phase while in the compression phase the former is much higher. In addition, according to numerical results, dynamic ocean water pressure is over-predicted either in compression or suction phase, however, the level of over-perdition is higher in compression phase than suction phase. Furthermore, the effect of vertical component of earthquake is investigated. The results show that the addition of the vertical component of earthquake increases the compression dynamic pressure while the suction pressure is not affected.
Two-Dimensional Numerical Simulation of Flow Around Rectangular Structures With Different Aspect Ratios
Authors: Tian Xinliang , Ong Muk Chen , Yang Jianmin , Myrhaug Dag
Published: November 2011

Many marine and offshore structures have structural components with square or rectangular cross-sections, e.g., columns of semi-submersibles and tension-leg platforms, heave damping plates of truss spar platforms as well as ship stabilizers. Two-dimensional flow normal to the longer edge of rectangles with different aspect ratios, i.e. from a square to a thin plate, is investigated numerically in the paper. The simulations are carried out at Re = 21400 (based on the free stream velocity and the height of the rectangular cross-section) by solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω SST (Shear Stress Transport) turbulence model by using OpenFOAM. The hydrodynamic results are compared with published experimental data and numerical results. The paper also includes further investigations on the effect of different aspect ratios.
A Basic Research on the VIV Response of Rotating Circular Cylinder in Flow
Authors: Rheem Chang-Kyu , Kato Koichiro
Published: November 2011

The characteristics of VIV response of rotating circular cylinders in flow had been investigated by both experiment and numerical simulation. In the experiment, the motions of a flexible circular cylinder pipe installed in a circulation water channel were measured. In simulation, a Discrete Vortex Method had been used to estimate hydrodynamic forces acting on a rigid circular cylinder. When a cylinder rotates in flow, a rotation frequency becomes important added to natural frequency and vortex shedding frequency. The deflection of a flexble pipe peaked when the frequency ratio of rotation frequency to natural frequency was between 1.0 and 1.5. This is similar to increment of oscillation amplitude by a resonance of natural vibration and vortex shedding. The peak oscillation frequency of a rotating circular cylinder in flow decreased with increase in rotation number. The main axis of cylinder oscillation turned in the rotation direction.
Characterisation of Slug Flow Conditions in Pipelines for Fatigue Analysis
Authors: Reda Ahmed M. , Forbes Gareth L. , Sultan Ibrahim A.
Published: November 2011

Understanding the problem of slug flow induced fatigue damage is of particular importance to the reliable operation of pipelines. Slug flow across unsupported pipeline spans, pipeline crossings or vertical engineered buckle initiators, i.e. sleepers, produces dynamic motion in the pipeline resulting in cyclic fatigue stresses. In some cases, the dynamic effects will cause the pipeline to fail at a point of stress concentration. In other cases, however, these effects may be negligible. The current literature provides no guidance as to when the dynamic effects of slug flow must be considered. This paper gives guidance and describes how fatigue due to slug flow in pipelines, which would normally require dynamic analysis, can be quantified using simplified quasi-static analysis. The paper also presents a design process which could be used by pipeline engineers to determine the level of analysis needed, before embarking on more complex and expensive dynamic finite element.
Reliability Analysis of FPSO Broken Cable in Tandem Based on Weakest Failure Modes Theory
Authors: Sun Hai , Li Shang-zhang , Sun Li-ping
Published: November 2011

Broken cable analysis in tandem is one of the key safety problems of offloading. There have been many difficulties to evaluate the reliability of offloading due to the complexity of stress in main cable and mooring system. In this paper the broken cable risk analysis of mooring system is classified into several orthogonal weakest failure modes base on weakest failure modes theory, which are calculated respectively cooperated with the software calculation results by Ariane7. A dual-cable for FPSO in tandem has been considered in series-parallel system that combines the weakest failure modes theory has been proposed. The research in this paper is of instructive significance for the security analysis problems of offloading in tandem.
A Numerical Study on Water Flooding in a Damaged Oil Carrier
Authors: Cheng Liang-Yee , Gomes Diogo Vieira , Yoshino Adriano Mitsuo , Nishimoto Kazuo
Published: November 2011

The objective of the present paper is to carry out numerical simulations on the coupled transient processes of oil leakage, water flooding and study of the stability in a damaged crude oil carrier. For this purpose, numerical approach based on Moving Particle Semi-Implicit (MPS) method is applied to model the complex fluid-solid interaction problem with free surface and oil-water multiphase flow. Changes on the modeling of the towing tank utilized in a previous study on oil leakage carried by the author are done to reduce the undesirable effects of the wave reflection. As a consequence, the improved results of the transient behaviors of hull motions are obtained for the cases with oil leak, as well as the final list angle and volume inside the tank in cases of water flooding. The results of the simulations show that the volume of flooded water is inversely proportional to the filling ratio. Also, the height of the opening has not significant effect on the final list and flooded volume.
Experimental Study on Fatigue Strength of Welded Joints Under Storm Loading
Authors: Moon Chang-Hyun , Hashimoto Kiyoshi , Song Yooseok , Kim Kyung-Su , Kim Sunghoon , Kim Bong Jae , Suh Yongsuk , Shim Yong Lae
Published: November 2011

Welded joints are important for fatigue strength evaluation of ship and offshore structures. However, current techniques for fatigue evaluation of welded joint under variable load is not accurate enough. Also, it cannot consider the effect of load history which is one of the important features for the variable loads. Therefore, many experimental attempts are conducted for storm model to consider the variable loading. However, studies of storm loading usually ignore the effect of calm sea loading which constitute a large portion of the marine phenomena. Because it has been believed that the contribution of calm sea loading is not dominant for fatigue life in storm loading. In this paper, fatigue tests are conducted for the specimens with transverse attachment made of high tensile steel under variable amplitude axial loading based on storm model. Considered loadings include repeated single storm, 6 or 8 kind storms sequenced randomly, and storms including calm sea condition while the mean stress and the maximum stress of loadings are changed. Moreover, the effect of three variables are investigated; 1) root mean square (RMS) value of stress amplitude, 2) mean stress shift and 3) maximum stress which can characterize the storm loading on fatigue life. In addition, experiments with calm sea loading are conducted and the effect of calm sea loading is also investigated. The storm and calm sea loadings are generated from IACS-34 wave scatter diagram. 5% strain drop criteria is introduced to define crack initiation life. Experimental results including the test results from previous study are evaluated and compared with DNV-CN 30.7 (2005) and Matsuoka’s method for the estimation of crack initiation and propagation life. From the result, it is concluded that the fatigue strength under storm loading can be evaluated by RMS value of stress amplitude. And mean stress shift is more likely to relate to fatigue strength than maximum stress. The effectiveness of the calm sea loading is depend on the existence of mean stress shift. Regarding fatigue life evaluated by DNV and Matsuoka method, both of them have almost same accuracy.
A Study on the Application of Cryogenic Design Criteria to a Self-Supporting Prismatic IMO Type B LNG Tank Made of SUS304(Mod)
Authors: Kim B. J. , Chung S. W. , Suh Y. S. , Shim Y. L. , Lee H. S.
Published: November 2011

IMO independent type B LNG tanks are designed using model tests, refined analytical tools and analysis methods to determine stress levels, fatigue life and crack propagation characteristics. Currently the tank design is performed based on the mechanical properties of the tank materials at room temperature. However it is notable that the materials used for the tanks show enhanced yield and tensile strength at low temperature and this design advantage can be taken into account when giving further consideration to fatigue fracture and crack propagation characteristics. In this study, the application of cryogenic design criteria to an SPB (Self-supporting Prismatic IMO type B) LNG tank made of SUS304(Mod) is presented. The material properties of SUS304(Mod) have been obtained from a series of tensile, fatigue and crack growth rate tests at 25°C, −100°C and −163°C. A design temperature that takes account of the cryogenic operating environment is proposed and the estimation of the weight reduction compared to a room temperature design is also described.
Relationship Between Charpy V-Notch Impact Value and Fracture Mechanics Toughness: Added Value of Finite Element Analysis and Instrumented Impact Tests
Authors: Thibaux Philippe , Van den Abeele Filip , Burlot Philippe
Published: November 2011

Each structure is designed with resistance versus the fracture, which requires the knowledge of the fracture resistance of the material. If no fracture mechanics data of the material is available, a KJC can be inferred from the master curve approach. The master curve approach relates a fracture toughness of 100 MPAm1/2 to the impact transition temperature T27J with a shift of 18°C. Although this relationship was successfully applied to a large number of experiments, some steels deviate significantly from the previous relationship, which can even lead to non-conservative design. In the present paper, instrumented impact tests (Charpy V-Notch CVN) and compact tensile (CT) tests were performed on two materials, one thermomechanically (TM-) rolled and one normalized steel. The difference between T0 and T27J was found to be different for these materials. Furthermore, the normalized steel exhibits a smooth transition from brittle to ductile behaviour, while the TM-rolled material shows a very steep transition. Extra information is gained by combining the instrumentation of the impact test and the finite element simulations of both the CT and impact tests. From the instrumented tests, it is also possible to determine the load at unstable crack propagation, the amount of energy dissipated at that moment, the load at crack arrest and the energy dissipated after crack arrest. From the finite element simulation, one learns about the constraints ahead of the crack tip for both configurations. The investigation teaches us that the smooth transition of the normalized material is related to a high energy dissipated after crack arrest, while the TM-rolled material has a much lower crack arrest load. The difference between T0 and T27J is then discussed by decomposing the total energy in the impact test between crack initiation, propagation and arrest. It is compared with KJC, which determines the toughness at unstable crack propagation, by reviewing the literature and local stress states computed from finite element.
Fracture Toughness Testing and Validation of Pipeline Girth Weld Flaw Acceptance Criteria for Sour Service Under Large Strain
Authors: Wu You You , Yuan Wen Guo , Chong Tse Ven Steven , Tronskar Jens P.
Published: November 2011

Fracture toughness is one of the most important input parameters for assessment of pipeline girth weld failure capacity. For many new subsea pipeline projects there is a need to develop flaw acceptance criteria for pipeline installation considering the operation phase which may involve the transport of sour oil and gas and where the pipeline is exposed to large axial strain due to local buckling. Engineering Critical Assessment (ECA) performed using laboratory data based on conservative KISSC testing gives small acceptable flaw sizes which may be below the workmanship criteria for pipeline laying. DNV has conducted extensive research based on the requirements of DNV-OS-F101 and DNV-RP-F108, aiming to establish a method to develop J-R curves applicable for ECA of pipeline girth welds in sour service environment and a methodology to validate the ECA by segment testing in a laboratory-simulated sour service environment as per DNV-RP-F108.
Modeling Very Extreme Sea States (VESS) in Real and Synthetic Design Level Storms
Authors: Cardone Vincent J. , Cox Andrew T.
Published: November 2011

This paper addresses two questions critical for the successful real world application of the Cooperative Research on Extreme Seas and their Impact (CresT) Joint Industry Project (JIP) design methodology in harsh operating environments: (1) how accurately may very extreme sea states (VESS) be specified by modern numerical spectral wave models? About 20 storms in which VESS (defined as with significant wave height (HS) > 14 m) have been measured by various in-situ and satellite-mounted altimeters are hindcast and it is shown that when the meteorological forcing is accurately specified, a proven 3rd generation (3G) wave model provides skillful and unbiased specification of peak HS and by implication of the associated spectral properties. The second question addressed is: how do current 3G models behave when applied to even more extreme meteorological forcing than observed in the real storms studied? The same hindcast methodology is, therefore, applied to a population of synthetic hurricanes whose combinations of intensity and scale are predicted by deductive modeling studies of Gulf of Mexico hurricanes carried out following Hurricane Katrina (2004). The model results suggests that for a tropical cyclone to generate say peak HS > 20 m would require the peak wind intensity of a major hurricane (Category 3 or greater) combined with a larger size and faster translation speed than may be maintained by a tropical cyclone in tropical or subtropical settings. Large scale cyclonic and relatively rapidly translating storms with major hurricane force peak wind speeds indeed exist as a class of mid-latitude extratropical cyclones, dubbed “winter hurricanes”. Hundreds of such storms have been detected in global satellite altimeter data in virtually all major ocean basins. The peak sea states in the most extreme examples are also found to be simulated quite skillfully with the hindcast technology applied. The hindcast results are explored to infer the upper limit to the naturally occurring dynamic range of sea states in tropical and winter hurricanes.
Fatigue Master Curve Approach for Arc-Welded Aluminium Joints: Mean Stress Effects
Authors: den Besten J. H. , Huijsmans R. H. M.
Published: November 2011

Mean stress affects the crack propagation and fatigue performance of arc-welded joints. However, it is a tough phenomenon because of a complex combination of properties in the alternating material zones: weld material, Heat Affected Zone (HAZ) material and base material. First, modeling steps from weld notch stress distributions to weld stress intensity factors, to a non-similitude two-stage crack propagation model, to a fatigue master curve formulation are summarized. Focusing on base and HAZ material, Walker’s mean stress model is adopted as a result of a concise review and superior results shown in literature. However, its model coefficient γ is determined using a rational approach rather than curve fitting and a micro- and macro-crack propagation effect is distinguished. Subsequently, for base material, the crack propagation model is modified to incorporate loading induced mean stress effects. Validation using experimental crack propagation data shows promising results. In the HAZ, except loading induced mean stress, the welding process induced residual stress acts as high-tensile mean stress as well. The latter dominates the former in the micro-crack propagation region. Fatigue performance improvement, e.g. a result of Ultrasonic Impact Treatment (UIT), that reduce the high-tensile mean stress is included correcting the loading induced macro-crack propagation mean stress parameter. Finally, the fatigue master curve formulation is modified accordingly and mean stress effects in the HAZ are satisfactorily validated using weld toe failure fatigue test data, including some UIT results.
Quick Connection Couplings in the Permeated Gas Relief Systems of Flexible Riser End Fittings
Authors: Rabelo Alexandre S. , Motta Antonio M. R. , Romero Antonio P. G. , Nunes Joa˜o Paulo C. e S. , Padilha Jose´ A. P. , Brack Marcelo
Published: November 2011

The objective of the paper is to present a new conception for the permeated gas relief system of flexible riser end fittings. The new conception is based on a multi-function gas relief system, depending on the requirements established by the operators. The main function of the system is to relief the accumulated gas in the riser annulus. Due to the interconnection of the annulus to the external environment through the top end-fitting, other functions of this system may be required such as to allow fluid injection into the annulus or vacuum testing, for example. The presented conception of the permeated gas relief system is based on the usage of quick connection and disconnection couplings. It was firstly developed focusing the particular cases of submerged top end fittings but it can be applicable in both situations where the riser top end fitting is located either at an emerged or a submerged position. In the course of its development, the conception has led to different patterns of the system, depending on the different required functions. The gas relief system was conceived in order to allow — in an easy and quick manner, without the risk of flooding the annulus with seawater — the execution of typical operations like those required for installing a monitoring and control system, for injecting fluids into the annulus, for vacuum testing or, additionally, for removing any damaged relief valve from the end fitting in order to substitute it for a new one. The paper describes the components of the gas relief system for each required function. The idea is to have many interchangeable items of standardized sets that meet specific requirements, case by case. The performance of the permeated gas relief system is an important issue for flexible riser integrity.
Tsunami Attack Evaluation and Countermeasures for Moored Small Ships in a Port
Authors: Kobayashi Eiichi , Yurugi Kouhei , Koshimura Shunichi
Published: November 2011

There is increasing concern over the possibility of the occurrence of huge Toukai, Tonankai, and Nankai earthquakes in the Nankai Trough, located in the Pacific Ocean off Japan. It is estimated that there is a 50% probability of a tsunami being generated by an earthquake in this area over the next 30 years. A tsunami attack on the coast of Japan would not only increase the sea level, but would also create strong horizontal flows in bays and ports. In particular, along the coastal area of Osaka Bay, Japan, there are numerous small ports where pleasure ships and/or fishery boats are moored. Any small ships moored in these ports would be subject to violent motion by strong lateral flows, even if they are moored to each other. As a consequence, the mooring lines would be cut, ships would move uncontrollably, and causing damage to facilities. Thus, it is very important from the viewpoint of marine-disaster prevention to gain a better understanding of the motion of small vessels originating in tsunami flows and to develop countermeasures in the face of a tsunami attack. In this paper, basic analyses of the ship motions resulting from a tsunami attack are carried out, and possible countermeasures are investigated. First, we describe mathematical models approximating the flow of tsunami and the abrupt maneuvers of relatively small vessels while being moored. Next, numerical simulations of the lateral motion of moored ships resulting from a tsunami attack on a fishery port located in the Osaka Bay are carried out. Additionally, the possibility of relatively high tension to be generated along the mooring lines is evaluated. Finally, the results of computer simulations demonstrate that such hazardous phenomena can be addressed with appropriate countermeasures.
Station Keeping Adaptive Control of a Boat With Twin Gasoline Outboard Motors: Synthesis, Simulation and Sea-Trials
Authors: Fisher Aaron , VanZwieten James , Xiros Nikolaos I.
Published: November 2011

There are increasingly more areas in which automatic station keeping technology can be of great benefit for small boat operators. This trend stems from technological advances that allow for smaller and more portable instrumentation and gear, bringing down the necessary size of vessels, which ultimately reduces cost. However, smaller vessels find themselves more adversely affected by sea conditions and have limited thrusting capabilities. Currently a skilled captain is needed on these small vessels to hold position over the area of interest in the presence of wind, wave, and current disturbances. Implementation of an automatic station keeping controller would free the captain from constantly monitoring the navigational instruments, to more closely supervise onboard operations and keep watch for other vessels in the area. Station keeping technology is currently being perused by Florida Atlantic University to enhance the ability of its 33ft boat to make oceanographic measurements in the Gulf Stream pertinent to its ocean energy projects. Such ocean energy projects require water velocity and temperature measurements at specific locations as part of the efforts for assessment of the hydrokinetic and ocean thermal resource. This technology is also a pivotal part of the sea basing goal currently being pursued by the Navy, which would allow vessels to stay in close but acceptable proximity to one another. The ability to hold position over a desired location can also have many additional uses such as for fishing, conducting surveys, deploying instruments, and transferring cargo or personnel. This text presents a novel approach for doing station keeping, as thus far a system for station keeping on small vessels using only tied twin outboard motors has not been developed and applied to an ocean going vessel by industry or academia. These controllers have been developed using multiple fixed-gain and adaptive control algorithms. Using a custom sensor and control system mounted onboard the test vessel; navigational measurements are used to adjust the throttles and engine angle using these developed algorithms. The performance of each of these controllers has been quantified using both numerical simulations and at sea testing. Using the results from these tests, initial comparisons have been made that show the advantages gained by using adaptive control algorithms instead of fixed-gain control.
Validation of a New Wave Energy Converter (WEC) Modelling Tool: Application to the Columbia Power WEC
Authors: Cruz Joao , Livingstone Michael , Rhinefrank Ken
Published: November 2011

This paper introduces a new software package (WaveDyn) dedicated to the modelling of wave energy converters (WECs). It consists of a multi-body, nonlinear equation of motion solver with multiple modules: wave characterisation, hydrodynamic data loader, power take-off (PTO), moorings, and control. The software relies on external (commercially available) hydrodynamic solvers for the basic hydrodynamic inputs (e.g. hydrodynamic coefficients, first or second-order wave exciting force), while it introduces new features mainly in terms of the description of the structural restraints between each body in a WEC, the templates to describe the PTO (i.e. highly nonlinear, discontinuous descriptions of the PTO force / torque) and the ability to test different control algorithms. The software allows the calculation of all relevant dynamic loads, leading to the quantification of the WEC performance for a variety of input conditions and control modes. Its flexibility ensures that it can be applied to the vast majority of the WEC concepts being developed. As part of an ongoing validation effort, WaveDyn has been applied to a WEC being developed by Columbia Power Technologies, LLC (Columbia Power). This new concept consists of a three body floating point-absorber with two PTO modes (the relative pitch between each float — forward and aft — and a vertical spar). In this paper performance estimates calculated in WaveDyn are compared with results from 1:33 and 1:15 scale experiments obtained at Oregon State University, for both regular and irregular waves. The key findings show the strong correlation between the WaveDyn estimates and the experimental results, and are relevant to technology developers, project developers and investors with a specific interest in the wave energy field, as a validated software package will reduce the overall uncertainty in performance and loads predictions.