bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematically Varied Rogue Wave Sequences for the Experimental Investigation of Extreme Structure Behavior
Authors: Clauss Gu¨nther F. , Schmittner Christian E. , Hennig Janou
Published: October 2008

For an improved design of ships and offshore structures with regard to their behavior under severe weather conditions, wave height and steepness as well as the shape of the wave profile have to be considered. In this paper, the extreme New Year Wave as documented in numerous publications is varied with respect to wave height and period. These varied wave sequences are realized and measured in a model tank and applied to the investigation of motions and bending moments of an FPSO ship. The results are compared to the responses in the original wave train. An investigation of the riskiness of extreme wave sequences in comparison with existing rules concludes the paper.
A Numerical Feasibility Study of a Parametric Roll Advance Warning System
Authors: McCue Leigh Shaw , Bulian Gabriele
Published: October 2008

This work studies the practicality of using finite-time Lyapunov exponents (FTLEs) to detect the inception of parametric resonance for vessels operating in irregular longitudinal seas. Parametrically excited roll motion is modelled as a single degree-of-freedom system, with nonlinear damping and restoring terms. FTLEs are numerically calculated at every integration time step. Using this numerical model of parametric roll and through tracking trends in the FTLE time series behavior, warnings of parametric roll are identified. This work serves as a proof-of-concept of the FTLE technique’s viability in detecting parametric resonance. The ultimate aim of the research contained in this paper, along with future work, is the development of a real-time, on-board aid to warn of impending danger allowing for avoidance of severe, even catastrophic, vessel instabilities.
Front Tracking Approach and Application to Multi-Fluid Flow
Authors: Behera Manasa Ranjan , Murali K.
Published: October 2008

Multiphase flows simulations using a robust interface-tracking method, are presented. The method is based on writing one set of governing equations for the whole computational domain and treating the different phases as single fluid domain with variable material properties. Interfacial terms are accounted for by adding the appropriate sources as δ functions at the boundary separating the phases. The unsteady Navier-Stokes equations are solved by finite volume method on a fixed, structured grid and the interface, or front, is tracked explicitly by a lower dimensional grid. Interfacial source terms are computed on the front and transferred to the fixed grid. Advection of fluid properties such as density and viscosity is done by following the motion of the front. The method has been implemented for interfacial flow problems, depicting the interface and topology change capturing capability. The representation of the moving interface and its dynamic restructuring, as well as the transfer of information between the moving front and the fixed grid, is discussed. Extensions of the method to density stratified flows, and interfacial movements are then presented.
On the Non-Linear Analysis of Pipeline-Soil Interaction Dynamics on the Ocean Bed
Authors: Olunloyo Vincent O. S. , Osheku Charles A. , Damisa O.
Published: October 2008

The non-linear dynamic response interaction of a pipeline on a non-stationary ocean-bed is herein investigated where the pipeline is idealized as a beam on a non-linear elastic foundation. By employing regular perturbation and integral transform approach, this paper presents generalized closed form expressions for the natural frequency of vibration and the dynamic interaction response profile. In particular, the modulation of the natural frequency by flow parameters such as, the internal fluid transmission velocity, pipeline sediment cover and the geo-mechanical behaviour of the ocean bed are highlighted while the design implications for such transmission pipelines are analyzed.
Inventory of Canada’s Offshore Wave Energy Resources
Authors: Cornett Andrew M.
Published: October 2008

Global warming, the depletion of conventional energy reserves and the rising cost of electricity generation have sparked renewed interest in renewable wave energy within Canada and internationally. Significant advances in wave energy converters have been made in recent years, and there is a growing realization in many countries, particularly those in Europe, that these technologies will be ready for large scale deployments within the next five to ten years (ABP, 2004). Despite these recent developments, very little effort has been directed to quantifying and mapping wave energy resources in Canada in the past. This paper presents results from a recent study in which the wave energy resource in Canada’s Pacific and Atlantic waters is quantified by analysing a large quantity of data obtained from four sources: direct wave measurements; two wind-wave hindcasts of the North Atlantic; and a single hindcast of the Northeast Pacific. Each data source is described and the methods used to analyse the data sets are explained in detail. The derived wave power estimates, including their seasonal and spatial variability, are presented and discussed. Results obtained from the direct measurements and the wind-wave hindcasts are also compared. The paper also includes a review of the theoretical background required to estimate wave energy. The waters off Canada’s Pacific and Atlantic coasts are endowed with rich wave energy resources. The results presented here define the scale of these resources, as well as their significant spatial and seasonal variations.
On the Dynamic Behaviour of Offshore Foundation Footings in a Moving Ocean Bed
Authors: Olunloyo Vincent O. S. , Osheku Charles A.
Published: October 2008

The reliability of partly submerged production storage platforms deployed for the exploitation of geo-resources in deep and ultra-deep offshore locations is strongly influenced by the dynamic stability and performance of their foundation footings under hydrodynamic loading and external excitation. This paper presents an integral transform approach for investigating the effects of the three-dimensional motion of the gripping ocean bed subsoil layer under pressurized external excitation. For this, the fluid-foundation-soil dynamic interaction boundary value problem is modeled as an elastic plate on an elastic foundation. In particular, closed form expressions for the dynamic response profiles and the natural frequency of vibration as modulated by the ocean bed poro-mechanics are analysed and presented.
Qualitative Sloshing Computations for the Assessment of Membrane LNG Cargo Containment System Design
Authors: Park Tae-Hyun , Lee Young-Woo , Lee Hyun-Ho , Shin Hyun-Soo
Published: October 2008

Long duration numerical sloshing simulations and model tests have been carried out to assess membrane LNG cargo containment system design. In the sloshing model tests, resonance periods of the tank were taken into consideration for the selection of critical sea states in viewpoint of sloshing loads. For the sloshing scenario of the most probable highest extreme impact pressure used in sloshing model tests, impact pressures were calculated and statistically post-processed for critical locations in a cargo hold of LNG carrier using full scale 5-hour numerical simulations. In the numerical simulations, violent sloshing behaviors could be reproduced using a general-purpose commercial CFD code which uses PLIC VOF method to capture the free surface evolutions. For validation of the numerical calculations, 2-dimensional sloshing simulation was first performed for a rectangular tank and a good agreement with experimental data was shown. For use in the assessment of the tank design, 3-dimensional numerical sloshing simulations were performed using four degrees of freedom irregular ship motions and the statistically processed impact pressures were compared with those of the sloshing model tests. The comparison showed that the 3-dimensional long duration numerical sloshing simulation can be a qualitative computational tool for use in the assessment of the membrane LNG cargo containment system design.
Effect of Tensile Property Distribution on Strain-Based Design Application of High Strength UOE Line Pipe
Authors: Shinohara Yasuhiro , Tsuru Eiji , Hara Takuya , Asahi Hitoshi , Terada Yoshio , Doi Naoki
Published: October 2008

For line pipe to which a strain-based design is applied, control of mechanical properties such as yield to tensile strength (Y/T) ratio, yield strength (YS) and flow stress at a low strain is required. These mechanical properties generally change during thermal coating treatment. A high strength UOE line pipe that is less susceptible to strain aging has recently been developed. In UOE pipes, mechanical properties change along the circumferential direction. However, the strength distribution has received little attention. Furthermore, the extent to which the change in strength along the circumferential direction affects the strain limits in strain-based design application is unclear. In this paper, firstly, the pipe forming strain variation and mechanical properties distribution along the circumferential direction of the X80 UOE line pipe suitable to the application of strain-based design are presented. Secondly, change in the properties distribution after thermal coating application is examined. Finally, the effect of strength distribution on the strain limits in strain-based design is discussed.
Numerical Simulation of Small-Scale Turbulent Diffusion for Injected CO2 in the Deep Ocean
Authors: Hirabayashi Shinichiro , Sato Toru
Published: October 2008

Small-scale turbulent diffusion is numerically simulated in relation to its time variability dependent on tidal current. From time series of 3D (3-dimensional) velocity and temperature measured at the depth of 2000 m, main constituents of internal tides are extracted. Wavenumbers of eddies, the scale of which is O (102) m, are determined by Taylor’s frozen eddy hypothesis with time-varying tidal speed taken as advection velocity. Large eddy simulation was applied to generate turbulence numerically by forcing the measured low-wavenumber components in the computational domain. The result shows that the energy dissipation rate varies in time, ranging from O (10−11) to O (10−7) m2 s−3. These values of energy dissipation correspond with vertical diffusivity of 10−6 to 10−4 m2 s−1 in this area, with temporal average value of 6.9 × 10−5 m2 s−1.
Experimental Feasibility Study on CO2 Sequestration in the Form of Hydrate Under Seafloor
Authors: Inui Masayuki , Sato Toru
Published: October 2008

A new concept for CO2 geological sequestration is proposed here as one of promising countermeasures against the global warming. For general geological sequestration technologies, there are still some issues we need to tackle, such as the expansion of amount of sequestrated CO2, reduction of environmental risks caused by CO2 leakage, and cost saving. In order to solve these problems, we propose CO2 sequestration system to sequestrate a large amount of CO2 in the form of gas hydrate under the seafloor safely. In this system, we inject CO2 + N2 mixed gas recovered from flue gas of a coal-thermal power plant into marine sediments at high pressure and low temperature, where CO2 forms clathrate hydrate. Besides, by using CO2 + N2 mixed gas, we can reduce the cost for its sequestration and avoid blockage in marine sediments at the same time. In this work, we assessed the potential amount of sequestrated CO2 and the cost of this system. From the results, the amount of CO2 that can be sequestrated offshore Japan by this system was estimated to be twice and the sequestration cost can be reduced by 14.3%, compared with those of the CO2 aquifer storage.
The Dynamic Response of Gravity Type Quay Wall During Earthquake Including Soil-Sea-Structure Interaction
Authors: Gharabaghi A. R. M. , Arablouei A. , Ghalandarzadeh A. , Abedi K.
Published: October 2008

The dynamic response of gravity type quay wall during earthquake including soil-sea-structure interaction is calculated using ADINA finite element techniques. The main objective of this study is to investigate the effects of fluid-structure interaction on the residual displacement of wall after a real earthquake. A direct symmetric coupled formulation based on the fluid velocity potential is used to calculate the nonlinear hydrodynamic pressure of sea water acting on the wall. The doubly asymptotic approximation (DAA) is used to account for the effects of outer fluid on the inner region. The non-associated Mohr-Coulomb material behavior is applied to model the failure of soil. The full nonlinear effective stress analysis is performed in this study and the soil-pore fluid interaction effects are modeled using porous media formulation. Viscous boundary condition is implemented to model the artificial boundary in direct method analysis of soil-structure interaction system and sliding contact condition was modeled in the interface of wall and surrounding soil. A typical configuration of gravity quay wall is used for analysis and three real earthquakes excitation are applied as base acceleration. The results show that influence of fluid-structure interaction effects on the permanent displacement of a gravity quay wall constructed on relatively non-liquefiable site is not considerable.
The Robustness of the Added Mass in VIV Models
Authors: Cunha Leandro D. , Pesce Celso P. , Wanderley Juan , Fujarra Andre´ L. C.
Published: October 2008

In this paper we show that added mass coefficient, Ca, is robust, i.e., is a first measure of model consistency. Regardless of the model type, phenomenological as well as CFD models, the general trend of the added mass coefficient plot is always the same.
Application of Aluminium Alloys in a Structural Joint With Great Shear Deformation Capacity
Authors: Khonsari S. V. , England G. L. , Ghahramaninezhad-Gharehlar M.
Published: October 2008

A new structural connection, already discussed in previous papers, with very special and, in some respects, unique, features, such as having very high rotational capacity in bending, and high shear deformation capacity under shear, hence high energy-dissipation capacity under either type of loading, was developed. Specimens of either variant of this joint, fabricated with steel components, were already tested under bending and shear in a mainly separate manner. However, due to the particular shape of the connection, and its ability to be extruded in aluminium, in the most recent work the behaviour of its aluminium specimens under shear loading was studied. A series of specimens fabricated from various classes of aluminium alloys were tested whose results are reported here. All of the specimens except one were tested under ‘monotonic’ loading, and one specimen was tested ‘cyclically.’ Despite the deficiencies in the specimens caused by poor welding of their components, the results show the high shear deformation capacity of the aluminium specimens which was accompanied by appreciable strength.
Combination Factors Suitable for Semi-Probabilistic Design of Floating Production, Storage and Offloading (FPSO) Vessels
Authors: Huang Wenbo , Moan Torgeir
Published: October 2008

The paper derived new probabilistic models for still-water loads and the combined still-water and wave load effects of FPSOs. A procedure for determining load combination factors, which is suitable for semi-probabilistic and probabilistic design of FPSOs, is established. The most relevant load combination factors in harsh and benign conditions are derived.
Numerical Prediction of Bare and Straked Cylinder VIV
Authors: Constantinides Yiannis , Oakley Owen H.
Published: October 2008

The prediction of deepwater riser Vortex Induced Vibrations (VIV) is one of the most challenging areas in the offshore industry. Numerous experimental and numerical studies have been performed in an effort to improve the understanding and prediction of cylinder VIV behavior. This paper presents the numerical simulation of rigid circular sections, both bare and fitted with strakes, using a second order accurate finite element computational fluid dynamics (CFD) method. Two turbulence models are examined: the Spalart-Allmaras Reynolds Averaged Navier Stokes (RANS) and the Detached Eddy Simulation (DES). Pragmatic high Reynolds number simulations of fixed and moving cylinders are presented and compared with laboratory experiments. Flow visualization provides insights on how strakes mitigate VIV. Comparisons between RANS and DES results are also presented and discussed.
Do Winkler Models Work: A Case Study for Ice Scour Problem
Authors: Konuk Ibrahim , Yu Shenkai , Fredj Abdelfettah
Published: October 2008

The Arbitrary Lagrangian Eulerian (ALE) Finite Element (FE) ice scour model and two Winkler models are applied to different diameter pipes. One of the Winkler models is based on an empirical scour displacement function. The second Winkler model utilizes the soil displacements obtained from the continuum ALE model. The results from the Winkler models show that the strains and displacements experienced by the pipe are subject to large variations depending on how the soil is characterized. The results also illustrate that there are significant differences in the displacements and strains predicted by the ALE and Winkler models. It is shown that the Winkler models can be sometimes conservative and sometimes they calculate strains and displacements less than those predicted by the continuum ALE model.
Analysis on the Hull Girder Ultimate Strength of a Bulk Carrier Using Simplified Method Based on an Incremental–Iterative Approach
Authors: Ozguc O. , Das P. K. , Barltrop N. D. P.
Published: October 2008

The hull girder ultimate strength of a typical bulk carrier is analyzed using simplified method based on an incremental–iterative approach. First, vertical bending moment is examined by seven different methods. The moment versus curvature curves and the values of the ultimate longitudinal moments at collapse states are determined for both hogging and sagging cases. Secondly, the ultimate strength under coupled vertical and horizontal bending moment is accounted. An interaction curve is obtained corresponding to the results of series of calculation for the ship hull subject to bending conditions with different angles of curvature. It is found that the interaction curve is asymmetrical because the hull cross-section is not symmetrical with respect to horizontal axis and the structural response of the elements under compression is different from that under tension due to nonlinearity caused by buckling. The angles of the resultant bending moment vector and that of the curvature vector are different in investigated cases. The interaction design equations proposed by other researches are also addressed to discuss the results presented by this study.
Wave Forces on a Single Surface-Piercing Column: Comparisons Between Theory and Experiment
Authors: Masterton Stephen , Swan Chris
Published: October 2008

This paper concerns the nonlinear wave loads acting on a vertical, surface-piercing, column. New laboratory data is presented describing the loads acting on three columns, of varying size, subject to both regular and irregular wave fields; the latter corresponding to realistic JONSWAP spectra. In all cases the flow fields are such that the potential flow forces dominate; with the smallest column diameter lying well outside the linear diffraction regime (D/λ << 0.2, where D is the diameter and λ the wavelength) and the largest just within it. In each case a variety of nonlinearities are considered, together with a range of directional spreads. The measured data, describing the total base shear, and over-turning moment are compared to a second-order diffraction solution and a number of higher order potential force models. The results of these comparisons highlight those flow regimes in which the greatest uncertainty remains. Earlier work, reported by Swan et al. [1], corresponding to the smallest column diameter considered here, showed that the unexpected scattering of high-frequency waves may lead to additional nonlinear loading. The present data shows that the earlier results are in no sense typical of those occurring across the diffraction regime. Indeed, by considering a number of column diameters it is possible to demonstrate that there are a wide range of flow conditions in which the existing potential flow models provide an adequate representation of the applied loading; even in relatively steep waves. Nevertheless, there are also important flow regimes where unexpectedly large nonlinear or high frequency forcing can arise. The purpose of the present paper is to demonstrate both of these cases, to highlight the flow conditions in which each exists, and to comment on the wave conditions leading to the most extreme loading.
Time-Domain Simulations of Multi-Body Systems in Deterministic Wave Trains
Authors: Jacobsen Katja , Clauss Gu¨nther F.
Published: October 2008

A growing amount of reports on heavy lift operations involving huge crane vessels prove that investigations on the motion behavior of multi-body systems are vital regarding the combined aspects of safety and economics. In this paper a method of transforming frequency-domain into time-domain results is presented. With the panel program WAMIT (WAMIT Inc.) the Response Amplitude Operators (RAO) of the motions in six degrees of freedom of the structures involved in a lift operation are calculated. The multi-bodies RAOs differ significantly from those of the single structures (without interaction effects). The consideration of hydrodynamic coupling is therefore essential for the prediction of accurate relative motions between the structures. Frequency-domain results are still important when determining operational limitations. But only with simulations in time-domain the relation between cause and reaction can be studied in detail. Results from simulations provide for example decision support for finding uncritical starting points of the lift off operation. By Fouriertransforming the RAOs the impulse-response functions are obtained. Having the impulse-response function the time-dependent system responses in arbitrary deterministic wave registrations are determined by convolution. This method allows fast and effective time-domain simulations of multi-body systems. Results are presented for a crane semisubmersible and a conventional transport barge. The influence, particularly the sensitivity of wave height and wave length on the response is shown in wave packets.
Use of Supermartensitic Stainless Steel Pipe for Offshore Flowline Applications
Authors: Woollin P. , Kostrivas A.
Published: October 2008

Supermartensitic stainless steels (SMSS) have high strength and good resistance to corrosion in produced fluids containing CO2 and are cheaper than other competing corrosion resistant alloys. Hence, they are attractive flowline materials and they have been successfully used in a number of offshore applications. Nevertheless, service failures have occurred and two failure mechanisms in particular have caused difficulties at welds: (i) hydrogen embrittlement/ hydrogen induced stress cracking resulting from hydrogen picked-up under cathodic protection and (ii) intergranular stress corrosion cracking (IGSCC). This paper presents experimental data on each of these two failure phenomena and gives details of the currently available ways of avoiding these problems, highlighting where further information is required.
Experimental Evaluation of the Dynamic Air Gap of a Large-Volume Semi-Submersible Platform
Authors: Simos Alexandre N. , Fujarra Andre´ L. C. , Sparano Joa˜o V. , Umeda Carlos H. , Rossi Ronaldo R.
Published: October 2008

Definition of air gap is an extremely important issue in the design of floating offshore systems such as semi-submersible or TLP platforms. For these systems, any unnecessary increase in the static value of air gap generally demands the payload to be decreased or leads to a larger buoyant hull, which, in any case, has a negative effect on the project economics. Designers face a difficult challenge since there is no well-established methodology for predicting the air gap demand in the early stages of the design. This is a consequence of the inherent complexity involved in the problem of predicting the free-surface elevation around large structures in steep-waves, such as the largest wave expected during a design storm-sea spectrum. Non-linear diffraction models are usually called for a more consistent evaluation of the wave field under the deck and the wave run-up upon the columns, but even second-order analysis is not free of uncertainties. Therefore, air gap evaluation still relies heavily on experimental analysis. This paper presents some towing-tank results performed for the evaluation of the dynamic air gap of a large-volume semi-submersible platform. Regular wave tests were performed for the small-scale model in both restrained and moored configurations and results were confronted with numerical predictions. Air gap response at different locations of the hull was evaluated under three different sea states and results were compared to some semi-analytical models proposed in literature for preliminary air gap estimation. The role of dynamic coupling provided by a taut-leg mooring system on the air gap results is also discussed based on the experimental results.
Modelling of Periodic and Random Wave Forces on Submarine Pipelines
Authors: Aristodemo Francesco , Tomasicchio Giuseppe R. , Veltri Paolo
Published: October 2008

A numerical model for the prediction of the time variation of the flow field and the hydrodynamic forces on bottom submarine pipelines is proposed. The model is an extension for periodic and random waves of the Wake II hydrodynamic forces model (Soedigdo et al., 1999), originally proposed for sinusoidal waves. An extensive laboratory investigation has been carried out in order to calibrate the model. The numerical model is based on an analysis of the time history of the velocity field at each wave semi-cycle. A modified relationship of the wake velocity is introduced and the time history of the drag and lift hydrodynamic coefficients are obtained using a Gauss integration of the start-up function. The laboratory investigation was performed at the large wave flume of the Centro Sperimentale per Modelli Idraulici at Voltabarozzo (Padua, Italy). The tests were carried out by measuring the pressure values at 8 transducers mounted on a cylinder subjected to different periodic and random waves. The experiments refer to the range 4 ÷ 12 of the Keulegan-Carpenter number for periodic waves and to the range 4 ÷ 9 for random waves. The empirical parameters involved in the extended Wake II and in the classical Morison models were calibrated using the results of the sampled velocities and force time histories under different wave conditions. The comparisons between the experimental and numerical results indicate that the extended Wake II model allows an accurate evaluation of the peaks and of the phase shifts of the horizontal and vertical forces and is more accurate than the Morison model.
Sloshing Response of LNG Tank
Authors: Arswendy A. , Moan Torgeir
Published: October 2008

Static and dynamic stress analyses of Mark III insulation system for LNG containment considering sloshing impact pressures have been carried out. Various time and spatial characteristics of the loading was considered. A direct implicit time integration method was used for the dynamic analysis. Two structural models were applied, one in which the steel structure was modeled with a realistic flexibility and one in which the insulation was supported on a rigid foundation. The main focus was on the vertical stresses in the lower fiber of R-PUF, bottom plywood and mastic ropes. It was found that the static stress level of the lower part of the Mark III system based on the rigid steel plate support differed from one that based on the flexible steel plate support. The static stress level of the lower part of the Mark III system supported by a flexible steel structure varied and was higher above the stiffeners and less over the middle part of the plate. The largest natural period is about 1.5–8 milliseconds and, based upon the experimental results, the sloshing pressure is approximated by triangular function in time, with a characteristic duration of a few milliseconds. The effects of sloshing impact rise time and load patch on the maximum dynamic stress level of the lower part of the Mark III system based on the rigid and flexible steel plate support have been investigated. The results are presented in the form of the dynamic amplification factor. For impulse type sloshing pressures relative to the steel plate, the steel plate behaves as a rigid support, resulting in vertical responses that exhibit a limited variation over the area.
Status of the Atlas Elektronik’s Modular AUV Family
Authors: Hornfeld Willi
Published: October 2008

As opposed to ROVs (Remotely Operated Vehicles), self-propelled, unmanned autonomous underwater vehicles (AUVs) are becoming increasingly important since, unlike ROVs they can operate completely self-sufficiently, i.e. independent of the carrier platform and cable at practically any depth and for long periods of time, require only minor technical and logistic support and can be used in regions which are inaccessible to manned submersibles or ROVs (e.g. under ice regions). In other words, AUVs are distinguished by a wide range of applications, the extremely high quality of data collected, their very cost-effective operation and the large standoff capability to the carrier platform, the latter bringing about a distinct improvement in terms of carrier platform safety e.g. for military missions. Due to these advantages over conventional systems, AUVs can be employed for a whole variety of applications, such as the following in the commercial sector: • Sea Bed Mapping, • Pipeline and Route Survey, • Inspection/Control, • Site Clearance, • Debris Survey, • Science – Search – Environment – Geology, • Harbour and ship’s hull inspection. Moreover AUVs will play an important role in the military scenario like mine countermeasure as well. Obviously, one single type of AUV will be unable to cover this entire spectrum if — above and beyond the aforementioned applications — one considers the different operating depths ranging from coastal regions (about 10 m) to deep water (approx. 4000 m) and the various possible carrier platforms (helicopters, ships, submarines, shore stations). On the other hand, the development and use of one specific type of AUV for one or a very limited number of mission types would be very expensive, both in terms of costs involved and necessary logistics, and would hardly be acceptable on the market. The solution to this problem is the “modularity” of the AUV subsystems as well as a family concept for the vehicle design. To implement this strategy, ATLAS ELEKTRONIK has forced the development and marketing of an AUV family for a wide array of missions. The family starts with the SeaFox-IQ, a very small and lightweight (40 kg) AUV for 300 m diving depth, based on the extreme successful mine disposal ROV SeaFox. The big brother is the SeaStout, a 100 kg AUV, designed for 300 m too. The SeaOtter Mk1 and SeaOtter Mk2 AUVs are 1500 kg and 1100 kg vehicles for 600 m operations. The leading edge is the AUV DeepC, a 2500 kg experimental vehicle developed for 4000 m depth and up to 60 h endurance. The ATLAS AUV family offer a lot of hard- and software commonality to ensure that serviceability is maintained, while having a high degree of “customisation” in key areas like payload sensor selection ensuring they will meet customer needs.
Validation of a Three-Dimensional Large Eddy Simulation Finite Difference Method to Study Vortex Induced Vibration
Authors: Esperanc¸a Paulo T. , Wanderley Juan B. V. , Levi Carlos
Published: October 2008

Two-dimensional numerical simulations of Vortex Induced Vibration have been failing to duplicate accurately the corresponding experimental data. One possible explanation could be 3D effects present in the real problem that are not modeled in two-dimensional simulations. A three-dimensional finite difference method was implemented using Large Eddy Simulation (LES) technique and Message Passage Interface (MPI) and can be run in a cluster with an arbitrary number of computers. The good agreement with other numerical and experimental data obtained from the literature shows the good quality of the implemented code.
Airborne Electromagnetic Sea Ice Thickness Sounding in Shallow, Brackish Water Environments of the Caspian and Baltic Seas
Authors: Haas Christian
Published: October 2008

Ice engineering projects often rely on the knowledge of ice thickness in shallow, brackish water like in the Baltic and Caspian Seas. By means of field data and model results, the paper shows that helicopter-borne electromagnetic induction measurements using frequencies of 3.68 and 112 kHz can yield accurate thickness estimates with salinities as low as 3 ppt. The higher frequency yields the strongest EM signals. In addition, in shallow water the higher frequency is less sensitive to the sea floor signal, and can thus be used in water depths as shallow as 4 to 6 m, depending on flying altitude. Because the low frequency signal is very sensitive on shallow water depth, a combination of both signals will allow the retrieval of both ice thickness and water depth.
A New DNV Recommended Practice for Fatigue Analysis of Offshore Ships
Authors: Lotsberg Inge , Skjelby Tor , Vareide Kenneth , Amundsga˚rd O̸yvind , Landet Einar
Published: October 2008

During the last 10–15 years the industry has put significant focus on fatigue analysis methodologies for offshore ships. The reason for this is a larger cost consequence associated with fatigue cracks in these ships compared to traditional tankers. During these years DNV has gained experience from classification of offshore ships, experience from a number of detailed fatigue analyses of ships and FPSO’s and recommendations achieved through the joint industry project: “Fatigue Capacity of FPSOs”. Based on this DNV has found it appropriate to develop a Recommended Practice (DNV-RP-C206) for fatigue design of floating production, storage and offloading units and to link this document to classification services offered by DNV. The methodology can also be applied to other types of offshore ships. Some of the background and content of this Recommended Practice is presented in this paper.
Interaction Between Mooring Line Damping and Response Frequency as a Result of Stiffness Alteration in Surge
Authors: Johanning Lars , Smith George H. , Wolfram Julian
Published: October 2008

The design and operation of a chain mooring for a wave energy converter (WEC) is considered. Experimental measurements of a mooring line were conducted in the Heriot-Watt University wave basin at a scale of 1:10. The laboratory procedures were designed to resemble tests undertaken earlier in the year at ‘full’ scale in 24 m water depth. This paper describes and compares these measurements and relates the results to earlier work on mooring lines by Webster [1]. Measurements of both the damping and response frequencies of the mooring are described. Although the present results support partly the conclusions of the earlier work, care must be taken in how these are applied when one is considering mooring line design for WECs. It is concluded that there are significant differences for a WEC for both operational and limit state design in comparison with a more conventional offshore system such as an FPSO or CALM. Although the primary requirement is still one of station-keeping two further considerations may be of great importance. Firstly if a ‘farm’ of devices is to be considered then limitations in sea space may necessitate that the devices be relatively densely packed. This will mean that the ‘footprint’ of the mooring should be constrained, to ensure that the moorings from each device do not interfere with one another and this will have great significance for the loading experienced by the line. This can be exacerbated by variations in tidal range which will have a larger effect in comparison with a conventional deepwater mooring. A second factor may arise if the mooring system response is critical to the WEC energy extraction process. If the mooring becomes part of the ‘tuned’ system then changes in the mooring properties of damping and natural frequency could seriously affect energy conversion efficiencies.
HP-HT Pipeline Cyclic Behavior Considering Soil Berms Effect
Authors: de Oliveira Cardoso Carlos , da Costa Alvaro Maia , Solano Rafael Familiar
Published: October 2008

This article presents a numerical study for the Petrobras HP-HT pipeline P-53/PRA-1 that will be installed at Marlim Leste field in Campos Basin offshore Brazil. This pipeline will connect P-53 platform in deep-water (1031m) to an Autonomous Platform for Intermediate Pumping (PRA-1) in shallow water (100m). HP-HT pipelines resting on seabed can develop thermal buckling, which is an important concern for the pipeline structural integrity. The aim of this study is to verify the P-53/PRA-1 pipeline behavior during lateral buckling due to thermal cycles and pressure variations, using a new approach for the pipe-soil interaction model in contrast with the traditional Mohr-Coulomb friction model. The pipe-soil interaction model considers soil berms formed due to pipe cyclic displacements, representing different phases of the soil lateral reaction force versus displacement curve: breakout force, suction release, berm formation and residual resistance. The results presented compare the traditional Mohr-Coulomb model with the proposed one for several loads cycles, analyzing displacements, stresses and strains behavior during thermal buckling.
Submarine Pipeline Installation Joint Industry Project: Global Response Analysis of Pipelines During S-Laying
Authors: Torselletti Enrico , Vitali Luigino , Bruschi Roberto , Levold Erik , Collberg Leif
Published: October 2008

The development of deep water gas fields using trunklines to carry the gas to the markets is sometime limited by the feasibility/economics of the construction phase. In particular there is market for using S-lay vessel in water depth larger than 1000m. The S-lay feasibility depends on the applicable tension at the tensioner which is a function of water depth, stinger length and stinger curvature (for given stinger length by its curvature). This means that, without major vessel up-grading and to avoid too long stingers that are prone to damages caused by environmental loads, the application of larger stinger curvatures than allowed by current regulations/state of the art, is needed. The work presented in this paper is a result of the project “Development of a Design Guideline for Submarine Pipeline Installation” sponsored by STATOIL and HYDRO. The technical activities are performed in co-operation by DNV, STATOIL and SNAMPROGETTI. This paper presents the results of the analysed S-lay scenarios in relation to extended laying ability of medium to large diameter pipelines in order to define the statistical distribution of the relevant load effects, i.e. bending moment and longitudinal strain as per static/functional, dynamic/total, and environmental load effects. The results show that load effects (longitudinal applied strain and bending moment) are strongly influenced by the static setting (applied stinger curvature and axial force at the tensioner in combination with local roller reaction over the stinger). The load effect distributions are the basis for the development of design criteria/safety factors which fulfil a predefined target safety level.
Solution of the Boundary Layer Problems for Calculating the Natural Modes of Riser-Type Slender Structures
Authors: Chatjigeorgiou Ioannis K.
Published: October 2008

The present work treats the problem of the calculation of the natural frequencies and the corresponding bending vibration modes of vertical slender structures. The originality of the study lies on fact that for the derivation of natural frequencies and the corresponding mode shapes, all physical properties that influence the bending vibration of the structure were considered including the aspect of the variation of tension. The resulting mathematical formulation incorporates all principal contributions such as the bending stiffness, the weight and the tension variation. The governing equation is treated using a perturbation approach. The application of this method results to the development of two boundary layer problems at the ends of the structure. These problems are treated properly using a boundary layer problem solution methodology in order to obtain asymptotic approximations to the shape of the vibrating riser-type structure. It should be noted that in this work the term ‘boundary layer’ is not connected with fluid flows but it is used to indicate the narrow region across which the dependent variable undergoes very rapid changes. Frequently these narrow regions adjoin the boundaries of the domain of intersect, especially when the small parameter multiplies the highest derivative.
Sorption Kinetics of High Pressure Gases in Polymeric Tubing Materials
Authors: Jaeger P. , Buchner S. , Eggers R.
Published: October 2008

A gravimetric method was applied to determine the sorption kinetics of gases into polymers. Diffusivity as well as sorption capacity are determined directly. Data of gas permeability that are required for calculating leakage rates in polymeric flexile gas and oil ducts may be retrieved by multiplying the obtained diffusion coefficients and the gas solubility. In general carbon dioxide enters polymers to the highest extent. In industrial practice, the high solubility of CO2 e.g. may lead to explosive decompression of sealings once the operating pressure is reduced to atmospheric conditions. Diffusion coefficients are presented in the range of 75 to 130°C at 2 to 30 MPa.
Dynamic Wind Response: Effect of Sea Surface Roughness
Authors: Leira Bernt J. , Myrhaug Dag , Voll Jarle
Published: October 2008

The paper considers the surge-motion of a simplified dynamic system representing a FPSO exposed to wind load. The Ochi and Shin wind gust spectrum, [12], is used together with two sea surface roughness formulas: the wave age independent Charnock formula, [4], that is frequently used, and the wave age dependent Volkov formula, [16]. An example of results demonstrates the effect of the sea surface roughness on the dynamic wind response of the system.
Influence of Axial Force and Initial Curvature on the Flexural Deflection of Euler-Bernoulli Beam Structures Solved by DQEM Using EDQ
Authors: Chen Chang-New
Published: October 2008

The influence of axial force and initial curvature on the flexural deflection of Euler-Bernoulli beam structures is analyzed by differential quadrature element method (DQEM) using extended differential quadrature (EDQ). The DQEM uses the differential quadrature to discretize the governing differential equation defined on each element, the transition conditions defined on the inter-element boundary of two adjacent elements and the boundary conditions of the beam. Numerical results solved by the developed numerical algorithm are presented. The convergence of the developed DQEM analysis model is efficient. The theory presented in the paper can be used to effectively obtain accurate results in analyzing the offshore structures.
An Approximate Model for the First- and Second-Order Dynamic Response Analysis of Truss Spar Platforms
Authors: Sadeghi Keyvan , Incecik Atilla
Published: October 2008

A new simplified but efficient approximate model is developed for the first- and second-order dynamic response analysis of truss spar plarforms. The results obtained from this model are compared with the conventional numerical results and with experimental data where the validity of the model is verified.
Effects of Avoidance of Heavy Weather on the Wave Induced Load on Ships
Authors: Shu Zhi , Moan Torgeir
Published: October 2008

This paper is concerned with evaluating the effect of avoidance of heavy weather on the long term wave induced loads on ships. Two hydrodynamic codes VERES based on a 2D strip theory and WASIM based on a 3D Rankine panel method are employed to calculate the wave induced loads and motions on various vessels. Two models for heavy weather avoidance are proposed. The first is based upon the assumption that operational criteria relevant to vertical acceleration, green water and bottom slamming are fulfilled. The second one is based upon the assumption that the sea state forecasts are available to the ship master, and that rerouting is made. And based on the first model considering avoidance of heavy weather and the hydrodynamics results calculated from two codes, the wave induced hull girder loads are obtained. The results are discussed. In particular, the effect of different hydrodynamic codes and various scatter diagrams are assessed. After all, the long term prediction of wave induced hull girder loads considering the effect of avoidance of heavy weather will give a relatively more realistic evaluation of the extreme hull girder loads. Finally the results from ship rules will also be re-evaluated compared with the long term prediction with and without heavy weather avoidance.
Fatigue Damage From High Mode Number Vortex-Induced Vibration
Authors: Vandiver J. Kim , Swithenbank Susan B. , Jaiswal Vivek , Jhingran Vikas
Published: October 2008

This paper presents results from two field experiments using long flexible cylinders, suspended vertically from surface vessels. The experiments were designed to investigate vortex-induced vibration (VIV) at higher than tenth mode in uniform and sheared flows. The results of both experiments revealed significant vibration energy at the expected Strouhal frequency (referred to in this paper as the fundamental frequency) and also at two and three times the Strouhal frequency. Although higher harmonics have been reported before, this was the first time that the contribution to fatigue damage, resulting from the third harmonic, could be estimated with some certainty. This was enabled by the direct measurement of closely spaced strain gauges in one of the experiments. In some circumstances the largest RMS stress and fatigue damage due to VIV are caused by these higher harmonics. The total fatigue damage rate including the third harmonic is shown to be up to forty times greater than the damage rate due to the vibration at the fundamental vortex-shedding frequency alone. This dramatic increase in damage rate due to the third harmonic appears to be associated with a narrow range of reduced velocities in regions of the pipe associated with significant flow-induced excitation.
Anchor and Chain Reaction During Inclined Pullout in Clay
Authors: Song Zhenhe , Hu Yuxia , O’Loughlin Conleth D.
Published: October 2008

Plate anchors have attracted much attention in offshore deep water development. This paper studies anchor rotation and chain reaction during plate anchor inclined pullout when it is installed vertically in clay. Both numerical simulation of strip plate anchor and centrifuge model tests on square anchor are conducted in uniform and normally consolidated (NC) clay. In the numerical analysis, Remeshing and Interpolation Technique with Small Strain model (RITSS) is used to simulate large movements of the anchor. In the centrifuge model tests, a transparent “soil” is used to observe anchor rotation and chain reaction during anchor pullout. It is found that plate anchors reach ultimate capacity (Nc ≈ 11.7) when they are fully rotated to a position perpendicular to the pullout direction. During anchor pullout at 60° to the horizontal, the loss of embedment during keying-in ranges from 0.38 B to 0.58 B for square and strip anchors in uniform and NC soils. The loss of anchor embedment in NC clay is about 4% ∼ 23% higher than that in uniform clay depending on the soil strength profile in the NC soil.