bluuebunny/crossref_metadata_2025 huggingface dataset:
Full Scale Measurements of Fatigue and Extreme Loading Including Whipping on an 8600TEU Post Panamax Container Vessel in the Asia to Europe Trade
Authors: Heggelund Svein Erling , Storhaug Gaute , Choi Byong-Ki
Published: November 2011

Large container vessels are known to vibrate heavily in head sea storms due to its flexible hull girder, pronounced bow flare and high vessel speeds. Strong vibrations are mainly excited by bow impacts causing transient vibrations referred to as whipping. This whipping response increases both fatigue and extreme loading. Further resonance vibration by springing response is also well known to contribute to increased fatigue loading. On these large container vessels it may however not be only the vertical vibration mode that is excited but also horizontal and torsional vibrations (coupled). The current paper describes the measurement system installed on a vessel operating between East Asia and Europe. Sensors for global loading, local loading and transverse hatch opening distortions are supplemented by navigational and environmental data. The system is an extended hull monitoring system analyzing data onboard and providing decision support onboard as well as providing statistical and time series of data to shore for further assessment. The measurements confirm that the fatigue loading of critical details are dominated by the vibrations, and that the fatigue loading level in deck in a storm is higher than ever measured before, also leading to high extreme loads above IACS rule values. The full scale measurements do to some degree confirm previous model tests of the same vessel, but the real vessel has been operated at reduced speeds. So far the fatigue loading on this route is at a comfortable level, partly due to reduced speeds, but also the encountered sea states may be less severe than the route specific scatter diagram. The loading may however increase if the vessel speed is increased, and the loading may become uncomfortable high if the vessel is put on a more harsh trade like North Pacific (or North Atlantic). Also torsional and horizontal vibrations are observed, but the transverse hatch opening distortions are moderate. Stern slamming is not measured to any significant degree, but bow flare slamming is measured in the storms. Side shell fatigue loading is at a comfortable level due to the CSA-2 notation involving direct hydrodynamic load calculations in the design introducing a sufficient safety margin against fatigue cracks. Vibration is however contributing significantly also in the side shell. Only a few storms have been encountered so far. The fatigue damage is concentrated amidships and the affect of warping in front of the superstructure does not increase the fatigue loading to a level of concern.
Flowlines and Risers Pipes Ends Laser Measurement for Enhanced Girth Welds Manufacturing and Fatigue Behavior
Authors: Motta Lorenzo , Novelli Paolo , Darcis Philippe , Armengol Mariano , Tintori Federico
Published: November 2011

The paper describes the laser pipe end measurement systems developed by Tenaris to perform the automatic dimensional inspection of pipe ends (measuring OD, ID, WT) and the software’s applications which analyze the collected data. The measurements performed by the Laser End Measurement System (LEMS) can give great advantages to end users and laying companies allowing a more efficient pipe alignment prior welding. This is of particular importance in offshore oil recovery industry, where the fatigue requirements of pipelines subject to high dynamic loads are continuously increasing, as the exploitation is moving in harsh environments. Fatigue is normally the limiting design criterion for products like Steel Catenary Risers (SCRs) or fatigue sensitive flowlines, and it represents its major engineering challenge. One way to minimize the risks of girth welds’ fatigue failure is to minimize the pipes abutting Hi-Lo [1,2]. This task could be accomplished by the use of laser pipe ends measurements analyses in conjunction with dedicated software. This paper provides details on the implementation and validation processes of automatic measurement systems (fixed and portable) to determine pipe ends dimensions with precision and repeatability. In addition, the features and the capabilities of the fit-for-purpose to the end user automatic applications are showed. These features include the Best Matching (search of the alignments which minimize pipes abutting Hi-Lo), the Counter-Boring (analysis of the best ID/OD to which machine the pipe ends counter-bore and of the forecast of the machined WT after counter boring), and the sorting in families (determination of pipes groups according to their ID/WT/OD tolerances).
Simulation of a High-Energy Finfish Aquaculture Site Using a Finite Element Net Model
Authors: Nicoll Ryan S. , Steinke Dean M. , Attia Joseph , Roy Andre , Buckham Bradley J.
Published: November 2011

Over half of the seafood in the world today is produced through aquaculture. Many finfish species, such as Atlantic salmon, are farmed in permeable net pens in the ocean. Traditionally, these sites have been located in regions protected from high energy ocean swell, current, and wind. However, in areas such as Nova Scotia, Canada, there is a declining number of such protected locations available and so aquaculturists are moving into exposed sites. To safely operate at these sites, it is necessary to engineer the pens to withstand the forces of the open ocean. To conclusively assess finfish aquaculture equipment and moorings in open ocean conditions, Dynamic Systems Analysis Ltd. (DSA) has developed a finite-element net model (FENM) to interface with the dynamics simulation software ProteusDS. The following paper presents the development of the FENM and demonstrates the capability of the FENM to model wave and current loadings by comparing FENM simulations with published results from tank tests. In addition, the results of simulations of a full scale finfish aquaculture site in hurricane conditions are presented. The conditions were collected with an acoustic Doppler current profiler during hurricane Earl on September 4, 2010. The mooring line tensions from the ProteusDS simulation are compared against tensions measured during the storm with a Submersible Tension Logger (STL).
Experimental and Numerical Analysis of Forced Motion of a Circular Cylinder
Authors: Yin Decao , Larsen Carl M.
Published: November 2011

Vortex induced vibrations (VIV) of long, slender marine structures may cause severe fatigue damage. However, VIV is still not fully understood, which calls for further research on this topic. This paper discusses results from experimental and numerical investigations of forces on rigid cylinders subjected to combined in-line (IL) and cross-flow (CF) motions, and it aims at improving the understanding of the interaction between IL and CF response components. Model tests with a long flexible beam were conducted at MARINTEK for the Norwegian Deepwater Programme (NDP). The model was 38 m long and it was towed horizontally so that both uniform and linear sheared current profiles could be obtained. Orbits for cross section motions at selected positions along the beam were identified in these tests. Forced motion experiments using these orbits were later carried out in the Marine Cybernetic Laboratory at Norwegian University of Science and Technology (NTNU). A 2 m long rigid cylinder was towed horizontally and forced to follow the measured orbits with identical amplitude ratio, non-dimensional frequency and Reynolds number as for the flexible beam tests. Parts of the results from these tests were published by Yin & Larsen in 2010. In this paper results from an investigation of trajectories for six positions along the beam in a uniform current condition will be shown. Three orbits have nearly the same CF amplitude ratio at the primary CF frequency, and the other three have similar IL amplitude ratio at the primary IL frequency, which is twice the CF frequency. Hydrodynamic coefficients have been found from experiments and numerical computations were carried out to find vortex shedding patterns for these cases. The main conclusions are that the IL motion component is a significant influence factor, and that higher order displacement components are more pronounced in IL direction than CF. Significant displacements in IL direction at 6 times the primary CF frequency were also observed, the ‘2T’ vortex pattern was captured when strong IL motion components were present. It is also seen that hydrodynamic coefficients should be found for combined CF and IL orbits and thereby improve the empirical models for prediction of VIV.
Internal-Wave Sloshing in Triangular-Shaped Containers: A Numerical Study
Authors: Valentine Daniel T.
Published: November 2011

Computational solutions of sloshing phenomena in density stratified fluids in triangular shaped containers with the vertex of the container in the downward direction were investigated. Two of the typical cases are reported in this paper. The Navier-Stokes equations in terms of vorticity and stream function were solved by applying a second-order finite-difference computational method. A nearly two-layered continuously stratified fluid system is examined to investigate the motion of the pycno-cline that separates the lighter upper fluid from the bottom heavier fluid. The tilted side walls alter the sloshing significantly; in some cases vortex projectiles are ejected as the waves interact with the sidewalls.
Comparison of Methods for Short Crested Wave Analysis
Authors: van den Berg Joris
Published: November 2011

A comparison was made of the robustness and accuracy of Maximum Likelihood Method (MLM) and Maximum Entropy Method (MEM) short crested wave analysis using a small footprint probe array.
Lateral Buckling of Armor Wires in Flexible Pipes: Reaching 3000m Water Depth
Authors: Secher Philippe , Bectarte Fabrice , Felix-Henry Antoine
Published: November 2011

This paper presents the latest progress on the armor wires lateral buckling phenomena with the qualification of flexible pipes for water depths up to 3,000m. The design challenges specific to ultra deep water are governed by the effect of the external pressure: Armor wires lateral buckling is one of the failure modes that needs to be addressed when the flexible pipe is empty and subject to dynamic curvature cycling. As a first step, the lateral buckling mechanism is described and driving parameters are discussed. Then, the program objective is presented together with flexible pipe designs: - Subsea dynamic Jumpers applications; - Sweet and Sour Service; - Internal diameters up to 11″. Dedicated flexible pipe components were selected to address the severe loading conditions encountered in water depths up to 3,000m. Hydrostatic collapse resistance was addressed by a thick inner carcass layer and a PSI pressure vault. Armor wires lateral buckling was addressed by the design and industrialization of new tensile armor wires. The pipe samples were manufactured using industrial production process in the factories in France and Brazil. The available testing protocols are then presented discussing their advantages and drawbacks. For this campaign, a combination of Deep Immersion Performances (DIP) tests and tests in hyperbaric chambers was selected. The DIP test campaign was performed End 2009 beginning 2010 in the Gulf of Mexico using one of Technip Installation Vessel. These tests replicated the actual design conditions to which a flexible pipe would be subjected during installation and operation. The results clearly demonstrated the suitability of flexible pipes as a valid solution for ultra deep water applications. In addition, the DIP tests results were compared to the tests in hyperbaric chambers giving consistent results. This campaign provided design limitations of the new designs for both 9″ and 11″ internal diameter flexible pipes, in sweet and sour service in water depths up to 3,000m.
COOL™ Hose Qualification Process of the First EN1474-2 LNG Floating Hose
Authors: Queau Jean Pierre F. , Torre Giorgio E.
Published: November 2011

In 2005, SBM Offshore recognized that in future offshore Floating LNG Production Units, key enabling technologies would be required to ensure the safe and reliable tandem offloading to LNG Carriers. The foundation was thus laid down for the development of the COOL™ Hose: A cryogenic marine floating hose that would enable the tandem offloading between two vessels offshore. This paper presents, after an introduction to the COOL™ Hose design (Hose in Hose concept-HiH), the different steps in the qualification process following the EN1474-2 [1] guidelines and recommendations for design and testing of LNG transfer hoses. This qualification process has been endorsed by two Classification Societies ABS and DNV and has resulted in a Certificate of Fitness for Service from DNV and a Product Design Assessment Certificate from ABS making the SBM COOL™ Hose, the first EN1474-2 qualified LNG floating hose.
Time Domain Simulation of Two Interacting Ships Advancing Parallel in Waves
Authors: Xiang Xu , Faltinsen Odd M.
Published: November 2011

A 3D Rankine source method is developed to solve the initial-boundary value problem of two ships advancing in waves. Linear wave effects are considered. The two ships are assumed advancing parallel with identical forward speed, with or without stagger, and the Neumann-Kelvin flow is chosen as the steady basis flow. An artificial numerical beach is applied to satisfy the radiation condition. A fourth order Runge-Kutta method is used for the 12 degree of freedom dynamic solver of the two ships. The present solver is validated through studying linear radiation and diffraction problem of one or two ships by comparing with analytical or model test results. The coupled motion solver is applied to a single S-175 ship advancing in waves and two parallel advancing ships which were tested in the MARINTEK towing tank (Ronæss, 2002) and promising agreements are obtained.
Comparison of Solidification Behavior Between Underwater Wet Welding and Dry Welding
Authors: Al-Abbas Faisal M. , Al-Ghamdi Tariq A. , Liu Stephen
Published: November 2011

The solidification substructure, both mode and size, has influence on the mechanical properties of weld joints. Controlling the solidification substructure by obtaining finer grains will generally result in enhancement of the weld joint quality and properties. Thus, it is essential to understand how welding parameters including voltage, current and weld travel speed as well as the welding environment (air and water) affect the solidification substructure. This work presents the effects of welding parameters on columnar grain morphology for both wet and dry welds. Also it compares the solidification rate and columnar grain size (width and length) between the dry welds and wet welds. For fair comparison, the welding parameters of both dry welds and wet welds were maintained similar. The solidification rate of wet welds is faster than that for the dry welds. A maximum difference of 22% was observed at half distance from the fusion line to the weld centerline. For wet welds, the observations revealed that the average columnar grain width and length of wet welds decrease with increasing electrode angle and decreasing welding travel speed. On the other hand, the columnar grain width decreased with increasing welding current. Also, as the welding current increased the average columnar grain length increases. Dry welds differed from wet welds in that the columnar grain average length decreased as the welding current increases. Moreover, the wet weld columnar grains are finer than those found in the dry welds at low welding current, namely 110A and 120A, whereas the wet weld columnar grains are comparable or coarser at high welding current, e.g.130 A and 140A. Statistical analysis of the columnar grain aspect ratio data set using Student’s-t test resulted in low t-value, 0.329 for low current welds, while high t-value, 7.775, was obtained for the welds made at high welding current. Results revealed that the columnar grain morphology in wet welds and dry welds are statistically different at low welding current 110A while columnar grains in dry and wet welds are similar at high welding current 140A.
Hydrodynamic and Aerodynamic Loads on the Behaviour of Offshore Wind Farm
Authors: Gong Wei
Published: November 2011

Renewable energy provides a solution for complex current and future social and environmental problems whereas offshore industry has a large potential for providing renewable energy for future. Currently, offshore technology making use of wind for energy generation purpose becomes a hot spot with highly advanced research and development going on on one side and complex and critical problems present and difficult to solve on the other. This paper is trying to study problems related to the quantification of the hydrodynamic and aerodynamic loads for the design of offshore wind turbine support structures in the offshore wind farm. Both the hydrodynamic and aerodynamic conditions in the offshore site are extremely complex resulting in the difficulty of reasonable determination for the external loads on the wind turbine support structures. However, due to the increasing global demands for future energy solution, the design, analysis and optimization of offshore wind turbine is nevertheless an important issue. The paper first gives an introduction of the offshore wind farm and the complexity of the offshore environment. Wave load is explored with introduction of existing wave load models, comparison of their characteristics while the focus is placed on the nonlinear wave load by means of the Stokes higher order wave theory. Properties of a single regular wave based on methods of linear wave theory and Stokes higher order wave theory are compared which lead to differences in the results of wave load models when these two different methods are used. Wind load model is introduced briefly, followed by the introduction of current methods for determination or approximation of combined wave and wind load and also recommendations for practice. Park effect of the wind load and wave load is also introduced at limited depth in the latter stage as a direction for future research. Conclusion and recommendations based on all the above are therefore given at the last section of the paper.
A Piecewise Model for Prediction of Large Amplitude Total Ship Roll Damping
Authors: Bassler Christopher C. , Reed Arthur M. , Brown Alan J.
Published: November 2011

A piecewise model is presented to model total ship roll damping, with considerations for large amplitude roll motion effects, such as bilge keel interaction with the free-surface. The model is based on the consideration of distinct ship-specific physical phenomena, such as bilge keel emergence. Abrupt physical changes occur with these events, resulting in significant changes in the damping characteristics of the system. Without these considerations, roll motion may be under-predicted. Some additional considerations needed for the practical implementation of the proposed piecewise model are also discussed.
A Finite Element Model for Efficiency of a Moored Floating OWC Device in Regular Waves
Authors: Nader Jean-Roch , Zhu Song-Ping , Cooper Paul , Stappenbelt Brad
Published: November 2011

Hydrodynamic characteristics of floating OWC can be quite difficult to predict especially when a strong coupling is present between the chamber pressure and the device movements. Mooring properties, and air pressure inside the chamber can also considerably influence the motion of the device and therefore the energy output. A newly developed 3D finite element model based on the linear wave theory has been applied to a cylindrical type OWC device. The study focused principally on the effects of the mooring restoring force and pressure pneumatic damping in the chamber total volume flux and energy conversion of the device. Results show that properly chosen parameters could effectively increase the efficiency band width of such devices.
An Experimental Study of Effects of Water Depth on Wave Scattering and Motion Responses of a Moored Floating Breakwater in Regular Waves
Authors: Huang Zhenhua , Zhang Wenbin
Published: November 2011

Due to the mobility and low costs, floating breakwaters have been frequently considered as alternatives for protecting marinas and harbors from wave attacks. Main advantages of using floating breakwaters include (i) the exchange of water between a harbor and ocean, and (ii) an adjustable elevation varying with tidal levels. When floating breakwaters are used in shallow water environments (during low tides), the presence of seabed may affect the dynamics of the floating breakwaters. In the present study, a series of experiments were carried out in a wave flume of 1.5m wide and 45m long to study the effects of water depth on the performance of a moored floating breakwater. An inertial measurement unit mounted on the breakwater measures the motion responses. The wave reflection and transmission coefficients and the responses of the breakwater to regular waves are presented for four difference water depths.
Coupled Dynamic Modeling of a Moored Floating Platform With Risers
Authors: Jing Xiaoning , Webster William C. , Xu Qi , Lambrakos Kostas
Published: November 2011

A time domain coupled analysis capability has been developed to model the dynamic responses of an integrated floating system incorporating the interactions between vessel, moorings and risers in a marine environment. Hydrodynamic responses of the vessel allowing diffraction, radiation damping and wave drift forces on panelized bodies in addition to loads on Morison members, are modeled using the well-established program, MLTSIM. RodDyn, a finite element rod dynamics program, based on Garrett’s rod theory, is an efficient program to model the nonlinear dynamics of risers and moorings. The coupled MLTSIM-RodDyn suite integrates the nonlinear motions and structural analysis capabilities of RodDyn with the extensive hydrodynamic simulation capabilities of MLTSIM. With the fully-coupled dynamic analysis, the integrated system can be analyzed consistently. That is, the forces and moments applied by the rods to the platform are concurrent with the motions imposed on the rods by the platform at their multiple contact points. An asynchronous coupling of these two programs has been developed which allows for a fast simulation of this very complex problem. A worked example showing the nonlinear coupled analysis, is elaborated with systematical comparison with uncoupled analysis.
Development of Guidelines on Corrosion Resistant Steels for Cargo Oil Tanks
Authors: Yamaguchi Yoshiya , Terashima Shinpei
Published: November 2011

The International Maritime Organization (IMO) adopted new statutory requirements for corrosion protection of cargo oil tanks (hereafter referred to as “COT”) of crude oil tankers in May 2010. It is to be noted that these new requirements allow protection through the use of corrosion resistant steels as well as suitable coatings for COT. Corrosion resistant steels have been developed in Japanese steel mills based on the findings obtained in joint research project undertaken by the SR242 committee established in the Shipbuilding Association of Japan from 1999 to 2001. The project revealed corrosion mechanisms for general corrosion that occurs under the upper deck in inert gas environments and for pitting corrosion that occurs on the inner bottom. Corrosion resistant steels have excellent resistance against corrosion in these COT environments. The concept of protection through the use of corrosion resistant steels is based on the fact that such steels have been shown to better maintain their structural integrity during the target life of the ship by slowing down of the rate at which corrosion occurs compared with conventional steels. The IMO also developed performance standards for corrosion resistant steels together with statutory requirements for protection of COT. However, the maritime industry further seeks detailed guidelines on the unified application of such steels. In reply to their demands, ClassNK developed new guidelines specifying several matters for the suitable application of these steels, including on application range, combined application of corrosion resistant steels and coatings, test procedures for confirming the corrosion resistance of each product, and measures for ensuring the quality of welding work. This paper introduces an overview of the properties of corrosion resistant steels, IMO statutory requirements, and the newly developed guidelines.
Concurrent Design Introduction Activity at IHC Merwede
Authors: Fijneman Martin , Matthyssen Arne , Plat Robert
Published: November 2011

J-CDS and IHC Merwede have set up a programme to perform a hands-on introductory Concurrent Design (CD) Lite™ activity on a relevant subject. The goal of this CD Lite™ activity is to convey a first idea of the CD methodology to a selected team of IHC engineers. This activity will be evaluated to assess the potential and applicability of the full Concurrent Design methodology at IHC Merwede. Concurrent Design is a methodology for the early design phases. With a multidisciplinary team of stakeholders the design work is done in collocated sessions. The strong points of Concurrent Design are creating an integrated design in the form of parameters and enabling good communication and exchange of information between team members, including the customer. An activity consists of several clear phases: preparation, the collocated design sessions, followed by a reporting phase. The CD Lite™ activity consists of a preparation and two full days of sessions. The central questions for the sessions is to assess the scalability of two current trencher systems, a plough and a mechanical trencher, to cope with higher demands and requirements, most notably an increased target depth of the trench. The design is driven by reliability, availability and performance. In the sessions, the design team worked out two design options in three iterations and made comparisons between these to see in how far they are able to meet the requirements. The goal was achieved to provide some answers related to the trencher system questions for 2 options by performing 3 iterations per option. The main goal was achieved, i.e. in the short time of preparation and 2 days of sessions the CDLite™ experience has given the first insight to the design team and part of the management of IHC Merwede of the potential of Concurrent Design. The team members were positive about the CD methodology and the process. Positive remarks were given on the structured and transparent way of cooperation and the fast interaction that is possible with CD. The face to face communication was found very valuable. Having a team of experts in the room was perceived to be beneficial for the decision process. These experts can give a direct response to issues or problems, giving an insight on the impact of their decisions. Through working on a central database, it becomes clear what the relevant parameters in a design are in a design cycle. This approach is expected to improve the design process at IHC Merwede, especially in the field of innovative product developments that continue to push back the technical limitations in the maritime sector.
A Study on Improvement of Propulsive Performance of an Underwater Vehicle “PICASSO”
Authors: Suzuki Hiroyoshi , Watanabe Yoshitaka , Inoue Tomoya , Yamamichi Atsushi , Kitamoto Risa , Yoshida Hiroshi
Published: November 2011

This paper deals with the improvement of AUV/UROV’s hydrodynamic performance. Required hydrodynamic performance of AUV/UROV can be divided into propulsive performance and kinematic performance/maneuverability. Within these, propulsive performance of AUV/UROV is focused on this paper. Firstly, numerical and experimental methods are used to evaluate resistance performance of the original and changed body shape of a sample UROV. Secondly, we investigated the performance of a thruster equipped on the sample UROV. Finally, the balance point of the resistance of the bodies and thrust generated by thrusters is investigated and evaluate the efficiency for cruising.
Structural Integrity Management Framework for Mobile Installations
Authors: Stacey A. , Sharp J. V.
Published: November 2011

This paper presents a primary integrity management (PIM) framework for mobile installations (semi-submersibles and self elevating installations) and permanently moored floating installations (FPSOs, FSUs, etc.). The primary integrity of self-elevating and floating installations depends on both the primary structure and additional systems. The framework is based upon the UK regulatory requirements for offshore installations, including the need for a thorough review of the safety case accounting for any changes in condition and future plans and verification of the primary integrity management (PIM) process. Requirements and guidance are provided for all aspects of the integrity management process covering: • primary integrity hazard identification and risk control; • resources, organisation and management, including competency assurance; • information management and documentation; • primary integrity management policy, objectives and strategy; • inspection, examination and testing; • evaluation of structure and other primary systems; • maintenance, repair and upkeep; • audit, review and continual improvement. The framework also contains guidance based on the application of existing standards and industry published documents. Finally, guidance is given on the implementation of the framework.
Stochastic Response and Stability Analysis of Two-Point Mooring System
Authors: Banik A. K. , Datta T. K.
Published: November 2011

The stochastic response and stability of a two-point mooring system are investigated for random sea state represented by the P-M sea spectrum. The two point mooring system is modeled as a SDOF system having only stiffness nonlinearity; drag nonlinearity is represented by an equivalent linear damping. Since no parametric excitation exists and only the linear damping is assumed to be present in the system, only a local stability analysis is sufficient for the system. This is performed using a perturbation technique and the Infante’s method. The analysis requires the mean square response of the system, which may be obtained in various ways. In the present study, the method using van-der-Pol transformation and F-P-K equation is used to obtain the probability density function of the response under the random wave forces. From the moment of the probability density function, the mean square response is obtained. Stability of the system is represented by an inequality condition expressed as a function of some important parameters. A two point mooring system is analysed as an illustrative example for a water depth of 141.5 m and a sea state represented by PM spectrum with 16 m significant height. It is shown that for certain combinations of parameter values, stability of two point mooring system may not be achieved.
Operational Scour Management for Safe Jack-Up Operations
Authors: de Sonneville Ben , Raaijmakers Tim , Rudolph Daniel , Hunt Rupert , Rietema Klaas
Published: November 2011

Scour is an imminent threat for jack-up operations in shallow waters with sandy seabed conditions, strong tidal currents and/or a harsh wave climate, such as the North Sea. Jack-up operations in scour-sensitive areas require jack-up operators to evaluate the risk of scour and to adapt a scour management strategy in order to safeguard against foundation failure. Jack-up deployments are characteristically short term operations. This can be in the range of one day (construction project jack-ups) to several months (drilling units). Often, the strategy is to monitor scour and take remedial measures if and when required. An operational scour forecast and hindcast system was developed in order to assist jack-up operators with their management of scour. The system is based on automated importing and processing of metocean data (water levels, waves and currents) from operational metocean models or measurement stations and calculating forecasts for the temporal scour development with semi-empirical relations, derived from physical model tests for various types of foundations. During an operation, the results provide the basis for a periodic assessment whether, how much and where scour protection is required and when surveys should be performed. After an operation, the hindcast results serve as calibration for the scour prediction model and as evaluation of the scour management strategy. This paper presents two case studies for which the system was applied in the southern North Sea. In the first case study, the system was used to forecast scour around unprotected spudcans. A few weeks into the drilling operation, the operator decided to apply scour protection based on the warning that the predicted scour depth was reaching a critical value. A field survey performed after the scour protection installation confirmed that the predicted scour depth had been in line with the measured scour depth. The second case study comprised a drilling operation before which scour protection had been installed. The main objective of the system was to predict the stability of the scour protection and provide recommendations for scour protection maintenance and scheduling of scour inspection surveys. The field survey performed after the main storm event revealed that the predicted scour depth had been overestimated. A hindcast was performed to calibrate the scour model for future operations. It was concluded that the improved scour forecast system is an important milestone for scour management and contributes to improved safety in future jack-up operations.
CFD Simulation and Experimental Validation of a Vertical Axis Turbine: Toward Variable Pitch Cross-Flow Marine Turbine for Maximizing Hydropower Extraction—The SHIVA Project
Authors: Paillard Benoit , Astolfi Jacques-Andre , Hauville Frederic
Published: November 2011

The paper describes the numerical simulation of a cross-flow axis water turbine, widely known as Darrieus turbine or VAWT. The numerical solver is the RANSE solver CFX. The method of resolution aims at calculating the instantaneous forces on the blades of such a turbine, and the energy produced. Due to the specific blade kinematics that can result of pitch variable systems and the complex flow particularly in the centre part of the turbine, a meshing strategy based on the mixing of both sliding or/and deforming mesh were used. Due to the moderate Reynolds number involved in such systems, various fluid models were used including laminar flow, fully turbulent model as k–ω SST model and a laminar-turbulent transition model. A convergence study was carried out for time step, which yielded to courant number lower than 5 and angular step below 1° with about 600.000 cells with y+ = 1. Fixed pitch devices were simulated for comparison with experiments data available in the literature to validate the numerical model. The normal and tangential forces were compared for various flow conditions. The number of blades ranged from 1 to 3, the Tip Speed Ratio ranged from 1.5 to 7.5, the Reynolds number was about 4×104. It was observed that the agreement between the experiments and the numerical results is very good with the turbulent model in all cases excepted for one low TSR case for which the blade section incidence is maximum. Next step will consist in running simulations with variable pitch.
Can the Offshore Industry Benefit From Developments in the Dredging World?
Authors: Plat R. Robert , Hakkert M. P. Joti
Published: November 2011

The offshore and dredging industry increasingly converge. In this lecture we analyse the control tasks on board two trailing suction hopper dredgers and one multipurpose offshore construction vessel. Nowadays control and presentation systems on dredgers have evolved into highly automated systems which can be operated by only one person. — eliminating any chance of miscommunications or similar problems. This approach will be explained in full here. Given the proven benefits of the approach in the dredging industry, we make suggestions to apply it to control, automation and operation in the offshore industry. Our aim is to generate discussion about the real issues relating to the control of offshore vessels, and to obtain feedback.
Development of Biomimetic Underwater Vehicle for Offshore Investigation
Authors: Yamamoto Ikuo , Nakamura Tomokazu , Hanahara Hidemasa
Published: November 2011

The authors envisages a marine system network based on AUVs, offshore vessels, and air-crafts for realize sustainable development of the ocean. Then, a biomimetic underwater vehicle is expected to collect oceanographic data and water samples even in the complicated geographic area. The authors design and develop a flapping wing type underwater vehicle with flexible tail fin as a new biomimetic underwater vehicle. The flapping wing consists of multi-joints mechanism to get lift force and rotation moment for high maneuvering characteristics of motion. The tail fin is designed by elastic oscillating theory and developed to produce strong propulsion force for high speed maneuvering. In addition, a trim balance mechanism is designed to get the trim of pitch motion. The developed biomimetic underwater vehicle has higher maneuverability by strong lift force of flapping wing and propulsion force of tail fin. Also, the underwater vehicle can cruise quietly and avoid twining by seaweeds. The paper firstly introduces the next generation marine systems network concept. Then, it focuses on biomimetic underwater vehicles for mineral resource sensing and acquisition including the history of robotic fish development. Finally, it describes design method, numerical simulation, and tank test of the underwater vehicle with flapping main wing and elastic oscillating tail fin.
Application of Groebner Basis Methodology to Nonlinear Analysis of an Underwater Cable
Authors: Liu Y. Jane , Buchanan George R.
Published: November 2011

The governing equations for a large deflection cable analysis have a highly nonlinear and coupled nature. As a result, analytical solutions are unavailable or limited to a few simplified cases. The present study is to apply the Groebner Basis methodology combined with the Galerkin method to a geometrically nonlinear analysis of an underwater cable as an example.
The Motion Characteristics of Crawler Driven ROV Moving Over Bumps
Authors: Katsui Tokihiro , Akashi Masanari , Kajikawa Satoshi , Inoue Tomoya
Published: November 2011

Seafloor exploration and seabed resources development are important missions for solving international energy issues. The crawler driven ROV which is capable to do heavy works is considered as one of the probable systems for those missions and some have been developed already [1][2][3][4][5][6][7]. It is well known that the movability of actual ROVs on the sea floor is worse compared with the terrestrial crawlers [8][9][10][11][12]. Therefore it is important to make clear what conditions have to be satisfied for the stable running of a ROV on the sea bottom. The experimental investigation on the crawler based ROV’s movability suggests that light weight ROVs are easy to run in bow up condition and sometimes turn over. The authors have shown the condition for the normal running of the ROV which moves on the horizontal and inclined flat water bottom by means of a simple dynamic model [13][14][15]. This normal running condition is represented by the relation between the locations of gravity and buoyancy centers to be satisfied, in case of the weight, displacement, geometry and speed of the ROV are fixed. The model experiments have shown the validity of this normal running condition. However, the sea bottom is not flat and it is very important to know the moving performance of ROV over the bumps for the practical design point of view. In this paper, a method to estimate the ROVs’ ability to climb up the bumps is shown and it is validated by model experiments. The ROV model has two sets of crawlers; the rear crawlers are set horizontally and fore ones are inclined to climb up the bumps. The requirements to climb up the bumps for the design parameters of ROV such as crawler length, weight and displacement of ROV, location of gravity and buoyancy center, derived from present method agreed with the experimental results qualitatively.
Reliability Based Factors of Safety for VIV Fatigue Using NDP Riser High Mode VIV Tests
Authors: Fontaine E. , Marcollo H. , Vandiver K. , Triantafyllou M. , Larsen C. , Tognarelli M. , Constantinides Y. , Oakley O.
Published: November 2011

Understanding the level of conservatism in a riser system design for vortex-induced vibration (VIV) fatigue is an important issue for operators. This study represents a demonstration of the calibration methodology to derive consistent values for the Factor of Safety (FoS). The exercise is performed here based on medium scale VIV data and utilizing the most commonly used VIV prediction software by industry. The results emphasize the need for (i) a coherent approach to estimate the FoS to be used and (ii) monitoring/measurement of software improvements as this may increase risk of failure if the influence of such improvements on the FoS is not quantified.
Prediction of Water Wave Breaking Height and Depth Using ANFIS
Authors: Delavari Ehsan , Gharabaghi Ahmad Reza Mostafa , Chenaghlou Mohammad Reza
Published: November 2011

Wave height as well as water depth at the breaking point are two basic parameters which are necessary for studying coastal processes. In this paper, the application of Fuzzy Inference System (FIS) and Adaptive Neuro-Fuzzy Inference System (ANFIS) and semi-empirical models are investigated. The data sets used in this study are published laboratory data obtained from regular wave breaking on plane, impermeable slopes collected from 22 sources. Results indicate that the developed ANFIS model provides more accurate and reliable estimation of breaking wave height, compared to semi-empirical equations. However, some of semi-empirical equations provide better predictions of water depth at the breaking point compared to the ANFIS model.
Hydrodynamic Analysis of Semisubmersibles for a Large Scale Desalination Plant
Authors: Saravanan R. , Bhattacharyya S. K. , Panneer Selvam R. , Chandrasekaran Srinivasan
Published: November 2011

The estimation of the motion response of a floating semi-submersible type offshore platform for a desalination plant, of capacity 10 million litres per day (MLD) of fresh water, is the focus of the study. The platform needs station keeping by a mooring system using a spar moored in deep water. To cater to these requirements, several design configurations of the semi-submersible were tried out for their hydrodynamic performance in order to choose the best among them, in all cases keeping the cost of components at reasonable levels. The hydrodynamic analysis of the platforms was carried out using the software WAMIT. The natural heave period was the main criterion in finalizing the configuration of the semi-submersible because it has greatest impact on keeping the downtime of platform operation to a minimum. WAMIT yields unrealistically high RAO that is attributed to the effect of viscous damping not being incorporated in the analysis. Experimental investigation was carried out to find the viscous damping coefficient of the configuration of the semi-submersible that was finally chosen among a few alternatives. A 1:50 scale model was tested in the 4m flume at the Department of Ocean Engineering, I.I.T Madras. Free oscillation tests were carried out to find the damping coefficient and natural heave period. Use of experimentally obtained damping values in WAMIT yielded excellent comparison with experimentally obtained response values (RAOs). On the basis of the present work, configuration of a semi-submersible having six rectangular columns and two rectangular pontoons has been finalized for the desalination plant.
Comparison of Different Approaches for Fatigue Damage Accumulation in Steel Risers
Authors: Takafuji Fernanda C. M. , Martins Clo´vis A.
Published: November 2011

Fatigue is one of the main concerns of the offshore industry nowadays, since the failure of equipments could put not only the environment but also some people’s lives in danger. As described in DNV-RP-C203 and in DNV-RP-F204, the aim of fatigue analysis is to verify if a certain structure — in this case, a riser — will be able to operate adequately during a desired period of time, as well as to obtain information to program inspections. In a riser, the efforts vary along its length and also around its circumference. If one considers the stress around the circumference, the maximum stress point may change. To be realistic, one approach is to calculate the stress and fatigue life around the circumference. To be more conservative and also simplify the calculation, one could consider that the maximum stress always occurs at the same point. The purpose of this paper is to compare the fatigue life obtained with both approaches in order to verify the differences between them and verify how conservative that simplification can be. To perform the task, a steel riser is considered and the dynamic analysis is executed in time domain using Orcaflex 9.4. The fatigue is analyzed through the S-N Curve approach and the Miner’s rule is used to accumulate the damage.
Collisions Between Platforms and Ships in Norway in the Period 2001-2010
Authors: Kvitrud Arne
Published: November 2011

Since 1982, 115 collisions have been reported on the Norwegian Continental Shelf, with varying degree of severity. In the period 2001–2010 there have been 26 reported collisions. None of the collisions has caused loss of lives or personnel injuries. The economic consequences however have been significant, especially one collision in 2009. This paper will give statistical summaries of the events, and compare the development of events with previous periods. The focus will be on the six most severe cases, describing each case, the damage and emphasise the most common causes of these events.
FE Simulation of Cold Cracking Susceptibility in X70 Structural Steel Welded Joints
Authors: Olden Vigdis , Akselsen Odd Magne
Published: November 2011

Fracture mechanics SENT testing and FE simulation to establish hydrogen influenced cohesive parameters for X70 structural steel welded joints have been performed. Base metal and weld simulated coarse grained heat affected zone have been included in the study. The base metal did not fail at net section stresses lower than 1.29 times the yield strength and reveals low sensitivity to hydrogen embrittlement. The weld simulated coarse grained heat affected zone was prone to fracture at stresses above 64% of the yield strength, which indicates hydrogen embrittlement susceptibility. The cohesive parameters best fitting the experiments are δc = 0.3 mm and σc = 1700 MPa (3.5·σy) for the base metal and δc = 0.3 mm and σc = 2100 MPa (2.6·σy) for the coarse grained heat affected zone.