bluuebunny/crossref_metadata_2025 huggingface dataset:
Synergistic Effect of Seawater Environmental Factors on Carbon Steel Corrosion Rate
Authors: Atashin Sanam , Pakshir Mahmood , Yazdani Arash
Published: January 2011

Seawater is an aggressive, very corrosive, complex composition of different minerals covering about 70% of the earth’s surface that affects nearly all structural materials to some extent. Since seawater is a complex solution of many salts with various levels of physical and chemical parameters, the individual effect of each factor affecting the corrosion behavior is not readily separated, as is the case for a simple salt solution and an alteration in one may affect the relative effect magnitude of others, which illustrates the importance of synergistic analysis of dominant parameters. The synergistic effect of environmental factors on corrosion rate of carbon steel (AISI 1045) has been assessed in aerated synthetic seawater, using potentiodynamic polarization scan. The major environmental parameters considered are salinity, velocity, pH and temperature. A quantitative full two-level factorial experimental design method was applied to study the individual contribution percentage of each parameter on changing the average value of corrosion rate, as well as their interactive contributions. Because of the significant weakness of quantitative analysis in description and justification of variation direction the qualitative analysis has been assessed. The results show that the most contribution factor obtained by quantitative analysis is not always the most effective one obtained by qualitative analysis.
Synergistic Analysis of Seawater Parameters’ Effect on Corrosion Rate of Austenitic Stainless Steels 304 and 316
Authors: Pakshir Mahmood , Atashin Sanam , Yazdani Arash
Published: January 2011

In this research the synergistic effect of environmental factors on corrosion rate of austenitic stainless steels 304 and 316 has been assessed. The behavior and resistance of these alloys are studied in aerated synthetic seawater, using potentiodynamic polarization scan. The salinity, velocity, pH and temperature are the considered parameters. To study the individual and interactive contribution percentage of parameters on changing the average value of corrosion rate, a quantitative full two-level factorial experimental design method is applied. Beside this quantitative analysis, qualitative analysis has been used to predict the variation direction. By means of these two analyses we can predict the magnitude and quality of each parameter’s effect. This research has a potential in prediction of alloys’ behavior, which is really valuable in marine engineering designs.
Large-Scale Wave Kinematics Measurements of Regular Waves and Large-Amplitude Wave Groups
Authors: Minnick Lisa , Bassler Christopher , Percival Scott , Hanyok Lauren
Published: January 2011

An experiment was performed to measure and characterize wave kinematics in an experimental basin. The experiment is part of an ongoing effort to improve predictions and measurements of ship motions in waves, including more accurate characterization of the near-field wave environment and its influence on ship motions. The primary objective of this experiment was to measure and characterize the wave kinematics of regular waves of varying steepness and scaled irregular seaways, including irregular waves with embedded wave groups. Measurements, including free-surface elevations and velocity field measurements under the free surface, are presented and discussed.
Analysis of Marine Accident and Its Current Status in South Korea
Authors: Long Zhan Jun , Lee Seung Keon
Published: January 2011

More recently, there is a clear tendency to consider the improvement of safety as a vital factor in the marine industry. In this paper, general statistics of ship accidents in South Korea are considered and the main objective of this research is to investigate the causes and circumstances of all maritime accidents in the country from 1990 to 2007. The research carries out the most common causes of accidents on marine operation finally. This study result shows that safety problem really exists in the whole ocean industry and prevention of fatal accidents should focus on the research for the risk assessment and prediction methodology.
Study on Joint Return Period of Wind Speed and Wave Height Considering Lifetime of Platform Structure
Authors: Liu Wei , Dong Sheng , Chu Xinjie
Published: January 2011

Summarize the definition of design return period in existent codes and industry criteria. Joint return periods of different ocean environmental conditions are determined from the view of project life and risk probability. Based on equivalent bivariate maximum entropy distribution, joint design parameters of wave height and wind speed are estimated occurred in some place of Bohai Sea. The calculating results show that even if the return value of each environmental factor, such as wave height or wind speed, is small, their combinations usually lead to larger joint return periods. This will make the investment of ocean platform lower.
Prediction of the Depth of Shoe Pits After the Jack Up Penetration Into Seabed
Authors: Feng Han , Duan Menglan , Song Linsong , Zhang Qiyi
Published: January 2011

The penetration of the jackup platform will be much deeper, and the weight of the backfill above the spudcan will make more contribution to the resistance of jacking up of the platform. The prediction of the depth of the shoe pits is most important in estimating the weight of the backfill over the spudcan. This paper presents a method for predicting the depth of the shoe pits on the basis of superior limit theorem of ultimate analysis by comprehensively investigating the non-drained shear strength of backfill soil, the penetration depth and the spudcan shape. An experimental device is set up to verify the predicting formula, and very good results are obtained.
Experimental Study and Numerical Simulation on Slamming of High-Speed Trimaran
Authors: Kong Xiangshao , Wu Weiguo , Li Xiaobian , Xu Shuangxi , Zheng Yuanzhou , Huang Yanlin
Published: January 2011

The study on slamming of high speed trimaran is a very complicated and significant topic. Ship slamming is a nonlinear unsteady problem in which dynamic boundary and coupling among structure, air and water should be considered. It is a key issue in the ship research field. Unlike the slamming of ordinary monohull, trimaran slamming include not only main hull bottom slamming, but also slamming of trimaran cross structure, which makes trimaran slamming more complicated. In this paper, a reduced scale model of trimaran was constructed and an experiment was carried out in order to study the slamming pressure distribution on main hull and cross structure. By using nonlinear simulation software Autodyn, a finite element model was established to simulate the process that trimaran model enters into water. The accuracy and reliability of numerical simulation is validated by comparing experimental data and numerical simulation results. Furthermore, some valuable conclusions on trimaran slamming are obtained.
Harmonic Wave and Steady Current Effects on Plane Fishnets
Authors: Balash Cheslav , Colbourne Bruce , Bose Neil , Binns Jonathan , Raman-Nair Wayne
Published: January 2011

Individual and interaction effects of parallel current and waves on three plane nets were empirically examined. A current opposing the direction of the waves was shown to shorten the wavelength while a current in-line with the direction of the waves stretched the wave length. Due to these wave modifications, the combined loads produced by a current and waves were significantly less than the sum of current and wave forces applied individually. Applying a vector approach, the unsteady loads were split into drag forces and inertia components. Both components contributed considerably to the hydrodynamic loads for wave-only cases. For combinations of waves and current, the inertia force was significantly greater than the drag force. Further insights were also provided into the concepts of effective thickness and the modified Keulegan-Carpenter number as parameters quantifying inertia force and drag force for fishnets.
Numerical Simulation of Large Amplitude Sloshing in FPSO Tanks Under Irregular Excitations Based on Youngs VOF Method
Authors: Liu Yong-Tao , Ma Ning , Gu Xie-Chong
Published: January 2011

Recently, with the increasing demand for oil and natural gas in the sea promoted, large FPSOs (Floating Production, Storage and Offloading System) win people’s popularity. Large FPSOs with liquid tanks of large volume may suffer from random waves at real seas frequently, and this results in 6-DOF motions, such as roll and sway. Due to the excitations from irregular 6-DOF motions, liquid sloshing in tanks shows complicated behaviors. In severe sea states, violent sloshing yields great impact load to tank structure, even cause damage of tank structure. Since it is important to evaluate safety performance on liquid sloshing and its effects for large FPSOs, effective simulation of large amplitude liquid sloshing, including turning, merging, breaking of free surface et al, attracts researchers’ attention. Among all capturing methods for free surface, VOF is widely used for its simplicity as well as effectiveness. For the method to solve the VOF equation, Youngs method approximates free surface by oblique line in a cell, and possesses advantage of higher accuracy and higher sharpness for free surface capturing. Based on the establishments of basic control equations and boundary conditions, the authors establish numerical model for liquid motion using finite difference method. To solve the VOF equation, Youngs method [1] is adopted. And the velocity boundary conditions in free surface are specially analyzed. Finally a computer code for 2-D sloshing in time-stepping format is developed taking the above conditions into account. Considering characteristic FPSOs’ motions, roll, pitch and heave affect tank sloshing dominantly than others. In this paper, the authors predict such kinds of ship motions based on the strip theory, and take them due to irregular long-crest waves as compulsive external excitation, and numerically simulate large amplitude sloshing phenomenon in rectangular tanks of different filling level. Furthermore, the sloshing load to structure is also computed and some simulation results are compared with published experimental data.
Towards the Prediction of Hull Springing Response
Authors: Vidic-Perunovic Jelena
Published: January 2011

Research on wave induced vibration in ocean going ships has been undergoing the revival during the recent years. The increased flexibility in hulls owes to increase in ship size, primarily the ship length. Springing vibration is induced by unsteady pressure field on the hull and it decays slowly due to low structural damping and the recursive wave excitation. Due to its large number of cycles springing vibration may represent a fatigue problem in different ship forms — e.g. full form ships in ballast condition, ultra large containerships, fast passenger ships. Springing was a subject to many theoretical and experimental investigations during the last decades. In order to become a part of the hull design practice and to be considered explicitly springing calculation procedure must be well defined with a reasonable CPU time and accuracy. In the present study results from two different strip theories have been compared for an example ship. Further, the hydrodynamic pressure solution obtained by the radiation-diffraction panel method program has been employed by a hydroelastic strip theory in order to obtain the vertical wave excitation force on the hull. The influence of the diffraction wave pressure on springing prediction has been analyzed.
Prediction of Wave Crest and Height Distributions and Wave Groups Using a Numerical Wave Tank
Authors: Schmittner Christian , Kosleck Sascha , Hennig Janou
Published: January 2011

A major goal in current model test practice is the correct modeling of the environmental conditions, as they denote the starting point for all further hydrodynamic analyses. As a standard, wave power spectra are calibrated prior to the actual model tests whereas the corresponding wave group spectra follow from the arbitrarily chosen wave seeds and are not being predicted in advance. Wave crest and height distributions can be determined from the measured wave time traces at different reference locations in the basin but they are not calibrated purposely either. In this paper, a numerical wave tank based on a boundary element method is used to predict wave time traces measured in the wave basin. Resulting wave crest and height distributions are compared with theoretical distribution functions and wave measurements in MARIN’s Offshore Basin. Some thoughts on a possible application to the generation of “deterministic wave seeds” conclude the paper.
Experimental Investigation and Numerical Modeling of Hydrodynamic Force Characteristics of a Heaving Net
Authors: Ito Sho , Kinoshita Takeshi , Kitazawa Daisuke , Bao Weiguang , Itakura Hiroshi , Nishizawa Shinya
Published: January 2011

With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore sea cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. We investigated the hydrodynamic force properties of a heaving sea cage in the previous work and its results proved that the deformation of net much affects on sea cage’s motion characteristics. To study the most fundamental problem, we investigated the hydrodynamic force properties of an undeformable net in the present study. Nine net models are arranged. These models have square-shaped frame and its inner dimensions are 216 × 216 mm. In these net models, three different twine diameters and three different twine intervals are arranged. The porosities of these models are in the range of 0.39 to 0.91. In addition, an impermeable plate model is also arranged. Forced heaving tests and wave exciting force tests are carried out on each net and plate model. Added mass and damping coefficients, as obtained by forced heaving tests, differ according to porosity of net and oscillation frequency and amplitude. Wave exciting forces, as obtained by wave exciting force tests, also differ according to porosity of net and wave slope and the forces increase with wave amplitude in higher order than one. To compare with experimental results, we theoretically calculate the hydrodynamic forces from a linearized potential flow approach supplementing the effect of porosity. In the boundary condition on the net surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface.
The Application of Knee Brace Structure in the Design of Tension Leg Platform
Authors: Zhang D. , Deng Z. , Yan F.
Published: January 2011

Since its first use in offshore project for drilling and production platform in 1984, more than two dozens of Tension Leg Platform (TLP) structures have been installed in oil and gas fields. The trend for using TLP structure in the exploration of deepwater oil fields has also gained momentum in recent years. The major driving force behind this is because the TLP structure has relatively smaller heave motion, thus it can be used for dry tree application in deepwater. Knee brace has found applications in the design of TLP structures. These vertically diagonal structure members are mainly used to support heavy vertical loads when the column spaces are large. The applications of knee braces have been used for two different stages: the integration stage and the in-place stage. For large topsides, the integration of the platform is usually performed in two or more separate lifting. The knee brace is used to temporarily support the pieces of the topsides before they are integrated together. For conventional type of TLP structures, the top tensioned vertical risers (TTRs) are placed in the middle of the platform to stay away from the mooring system and other subsea systems. The large column-to-column space and heavy TTR loads create some technical and economic challenges for the design of deck structures. To effectively take these vertical loads, knee brace is used to cut down the span of the deck supports. The challenge for this application is how to effectively share the vertical loads while at the same time not to induce much global dynamic action on the knee brace structure. This paper will review the application of knee braces in TLP projects, study the impact of the knee braces to the global action of the hull and topsides structures, and discuss the results of the analysis through a project example. The study will concentrate on the global load distribution through the knee braces, and the interaction between the knee braces and the hull structure under the global load action. Analysis results will be presented and the impact of the knee braces to the global structure will be discussed. These results will show that with proper configuration layout, the knee brace can be designed mainly to take the vertical static load, thus minimize the participation of the dynamic effect. The Author will also discuss the pros and cons of the knee brace structure in TLP application and some key issues which deserve attention during the application.
Mechanical and Thermal Qualification of an Electrically Heated Pipe in Pipe (EH-PIP) and Application to Subsea Field Development
Authors: Denniel Sylvain , Hall Scott , De-Naurois Hever , Parenteau Thomas , Gooris Franc¸ois
Published: January 2011

TOTAL and TECHNIP have decided to undertake the Evaluation Qualification (LEVEL 2) of the innovative technology of ELECTRICAL HEAT TRACE (EHT) as a solution for active heating of subsea flowlines within Electrically Heated Pipe-In-Pipe (EH-PIP), in order to face the production challenges of oil reservoirs with high flow assurance constraints (wax, gel and critical hydrate appearance temperatures). The EH-PIP is a standard reelable PIP system complete with trace heating cables wrapped in a helical pattern around the inner pipe (flowline), below the insulation. This paper reviews some of the processes that were undertaken to provide resolution of the identified uncertainties and demonstrate the high reliability of the system during construction, reel-lay installation and then during the various phases of operation, including line preservation and restart after planned or un-planned shut-down. The thermal qualification tests assess the thermal behavior of the EH-PIP, confirming its high heating efficiency (around 90%), and demonstrating its ability to maintain a uniform flowline temperature in all cases, including in the “degraded mode” with only one trace heating cable remaining operating. The Numerical Computational Fluid Dynamics (CFD) tools were validated against the full scale (OD) thermal test results, and allow the simulation of EH-PIP behavior in all field development conditions allowing further evaluation of the system performance. Furthermore, long term ageing tests on cables and associated connections have confirmed the long term integrity of the heating products.
Deepwater Seafloor Resource Production: Development of the World’s Next Offshore Frontier
Authors: Smith Glen
Published: January 2011

A new seafloor resource industry is today focused on the exploration and recovery of high-grade copper and gold in seafloor massive-sulphide (SMS) mineralization. Work is in progress to commercially develop the first such deposit (Solwara 1) in 1,600 meters water depth in the benign Bismarck Sea, Papua New Guinea. Environmental, geological and engineering studies conducted to date have culminated in a number of world firsts, including the first Environmental Permit granted for the extraction of SMS deposits and the first NI 43-101 compliant SMS deposit resource statement. Design of the mining system has been based on proven deepwater technologies from the oil and gas industry. Pipeline trenching units, ROVs, deepwater production risers and drill cuttings removal systems will be adapted to initiate this new and exciting industry.
Comparison Between Theoretical and Experimental Flexible Pipe Bending Stresses
Authors: Sævik Svein
Published: January 2011

This paper presents alternative finite element formulations for predicting the dynamic stresses of tensile armour in un-bonded flexible pipes. Shear interaction in terms of friction stick-slip between layers is treated in two alternative ways; either by considering the cross-section resultant in terms of the friction moment or by applying a sandwich beam formulation for each individual tendon. For both formulations, the boundary condition in terms of initial contact pressure from static loads are treated by a separate model. Experimental studies applying fibre-optic Braggs are presented to validate the performance of the formulations in terms of dynamic stresses.
Design Analysis of a Weight Added Wave Configuration of a Flexible Riser in Shallow Water
Authors: Zhang Yanqiu , Tan Zhimin , Hou Yucheng
Published: January 2011

A flexible riser configuration design in shallow water, having a large variation in riser content density, can pose a real challenge and results in significant riser immersed weight alternation particularly evident in pipes with large internal diameters. In this scenario, it is extremely difficult, if not impossible, to meet the minimum clearance at both the top (to the vessel bottom or the water’s surface) and bottom (to the seabed) in an extreme environment by using a traditional wave configuration. An innovative riser configuration concept based on the traditional lazy wave, referred to as weight added wave (WAW), has been developed with a proactive self-control mechanism to ensure riser configuration compliance during excessive weight changes [1]. The self-control mechanism consists of the traditional buoyancy modules with the addition of strategically positioned weight chains. This paper presents both an advanced and a simple structural model utilized in the WAW riser configuration study. The advanced model accounts for the individual buoyancy module and weight chain in detail.
The Bearing Capacity of a Skirted Two-Foundation System
Authors: Yun G. J. , Oliphant J. , Maconochie A. , Ahmad A.
Published: January 2011

A foundation system comprising two closely spaced skirted rigidly connected foundations has been developed for in-line subsea structures on a number of offshore deepwater development projects off the west coast of Africa. Here the pipeline and its holding system are placed between the foundations and allowed to rest on the seabed during operation. This type of foundation system produces benefits during installation as the hydrodynamic forces on the structure are reduced and in operation a greater stability is achieved through a lower system centre of gravity. In addition, as the pipeline interacts with the seabed between the foundations, some of the pipeline loading is carried by the soil rather than the foundation system. There is no established design methodology for these foundation systems. Full interaction between the skirted two-foundation system occurs as the soil between them is constrained. Therefore, efficiencies in the vertical bearing capacity of a spaced skirted foundation system can be mobilised through foundation interaction provided by the structural connection. Previous work on uniform clay found that a maximum vertical bearing capacity efficiency of 1.05 was observed when the spacing between the two foundations or footings was approximately 0.25B. A series of plain strain FE analyses have been conducted to investigate the vertical bearing capacity of a skirted two-foundation system. Both uniform and non-uniform clay models have been studied. A parametric study has also been done to investigate the influence of the size of the spacing between foundations and skirt lengths on the overall foundation capacity.
Hydrodynamic Behavior of Overtopping Wave Energy Converters Built in Sea Defense Structures
Authors: Victor Lander , Kofoed Jens Peter , Troch Peter
Published: January 2011

Many sea defense structures need to be adapted to the rising sea water level and changing wave climate due to global warming. The accordingly required investments open perspectives for wave energy converters (WECs) — that are built as part of the sea defense structures — to become economically viable. In this paper the average overtopping discharges q of overtopping wave energy converters built in sea defense structures are studied. Physical model tests with this type of devices have been carried out in a wave flume leading to experimentally determined values for the average overtopping discharge q. These experimental data are compared with predicted average overtopping discharges using existing empirical formulae from literature — derived mainly for sea defense structures. Overtopping WECs have small relative crest freeboard heights and smooth slopes to maximize overtopping, which is contradictive to the basic role of sea defense structures. As a consequence, the experimentally achieved average overtopping discharges are situated in a range that is not well covered by the existing traditional prediction formulae. The presented results for linear-slope overtopping WECs fill the gap between those for smooth dikes and those for plain vertical walls. The overtopping behavior in that particular range is discussed in this paper.
Site Specific Wave Characterisation for Marine Energy Applications
Authors: Davey Thomas , Venugopal Vengatesan , Ingram David M. , Smith Helen C. M.
Published: January 2011

In order to conduct effective resource assessment for the marine energy industry the applied analysis techniques must be consistent and practicable. It is therefore important to establish the parameters of interest when characterising a sea state. A number of parameters for describing the shape of individual waves in the time-domain are examined. These parameters are used to characterise wave records from three selected sites: The European Marine Energy Centre (EMEC), UK; The Wave Hub test site, UK and the North Alwyn platform east of the Shetland Islands.
An Application of Design Load Generator to Predict Extreme Dynamic Bending Moments
Authors: Kim Dae-Hyun , Troesch Armin Walter
Published: January 2011

Two important components of dynamic bending are wave-induced bending and impact-induced whipping. Traditionally, dynamic loading has been incorporated into design load estimations via rule-based design approaches, most of which are inherently empirical. However, rule-based approaches may not guarantee a robust design in an unconventional system where experience is limited or operational requirements are rather special. To address this limitation, a Design Load Generator (DLG) is applied to construct an ensemble of short input time series that will return target extreme events at a preset time. To calculate the target extreme events, the DLG utilizes optimized non-uniform Fourier phase distributions. For nonlinear simulations, the current DLG requires an additional nonlinear simulator. To account for the nonlinearity associated with the dynamics of ship motion and to calculate the whipping response due to hull bottom slamming, the Large Amplitude Motion Program (LAMP) developed by Science Applications International Corporation (SAIC) is used. A Joint High Speed Sealift (JHSS) concept of the U.S. Navy is chosen to illustrate the current DLG methodology. The target extreme midship bending moments from the DLG are compared with the results from a short-term Monte Carlo simulation in the Weibull space to demonstrate the potential of the methodology.
CAD Software for Cable Design: A Three-Dimensional Visualization Tool
Authors: Provasi Rodrigo , Meirelles Christiano Odir Cardoso , Martins Clo´vis de Arruda
Published: January 2011

The concept and project of umbilical cables and flexible pipes are not simple tasks, due to the great variety of components and possible arrangements. The design of those elements is based on the functions they are intended to perform. Also, some structural characteristics determine which component will be selected, including electrical cables and hydraulic hoses, to control underwater equipment, protective sheaths, helically wounded tensile armors, anti-wear layers, interlocked carcasses; pressure armors and so on. The modeling process consists on defining the cable features and selecting the elements that will compose it. The process should take into account the desired structural characteristics, such as axial stiffness, and must respect some constraints, such as weight. To have an operational cable, one must follow a number of steps from definition to validation of the cable and any tool that provides a easier way to deal with this process is highly desired. In this scenario, Computer Aided Design software was conceived. It enables the definition of cable elements and set its relative arrangements in a cross-section view. Post-processing features are also part of the program, enabling users to visualize the geometry, determining possible interferences only visible in a three-dimensional visualization module. Although a solver is also available to determine stress and displacements and, as a sub-product, the cable weight and equivalent stiffness, the CAD software can be easily integrated to other solvers, to provide pre and post processing resources. This paper gives a general description of the whole CAD system but focus on the three-dimensional module. Through the paper, an overview of the software is shown, pointing out the system requirements. Next, the user interface is described, showing its features and, to conclude, modeled cables geometries and some results are shown.
Proposal for a Shipborne AUV Refuel System
Authors: Blanco Max
Published: January 2011

Autonomous Underwater Vehicles (AUVs) are limited by the quantum of energy they can carry. Contemporary operational strategy is either to remove and replace the fuel source, or to refuel on-deck. Both strategies require the vehicle to surface, be recovered and be relaunched. This proposal obviates the time inefficiency by a novel arrangement of a shipborne electromechanical cable combined with a deepwater vehicle dock, similar to the concept of aerial refuel. A theoretical prototype is analysed with the aid of a steady-state three-dimensional cable mathematics. Its aim is to predict the length of cable required to place the device at a fixed depth below the ocean surface. A steady-state vibrational analysis predicts the natural frequencies of the device. The vortex-induced vibrations that can impact the device depend on velocity and cable diameter are prevented by the suitable choice of physical parameters.
A Fleet of Autonomous Underwater Vehicles to Locate Flight 447
Authors: Blanco Max
Published: January 2011

The recent accident of Flight 447 in the mid-Atlantic will serve as backdrop to this document. An introduction to the field of Autonomous Underwater Vehicles is produced and the present limitations therein. A proposal is made based on a near-term forecast of developments in this field to improve the location and recovery of the emergency beacons.
Effects of Hydrostatic Nonlinearity on Motions of Floating Structures
Authors: Cao Yusong , Tahchiev Galin , Zhang Fuwei , Aarsnes Jan V. , Glomnes Einar B.
Published: January 2011

This paper presents a method to account for nonlinear hydrostatic restoring force/moments on vessels of arbitrary hull shape. The method calculates the time-dependent hydrostatic load on a vessel based on the direct numerical integration of the hydrostatic pressure over the instantaneous “wetted” portion of the vessel’s hull surface. The 6-DOF equation of motion with the nonlinear hydrostatic load (replacing the linear hydrostatic load) is solved. The effects of the hydrostatic nonlinearity are investigated for a few practical hull shapes (including a cylindrical SPAR, a conical BUOY, and a VLCC-converted FPSO). The nonlinear hydrostatic loads are compared with the corresponding linear ones and the importance of the hydrostatic nonlinearity and couplings on the vessel motions is assessed.
Modeling of Spud-Can Penetration and Uplift Using the Coupled Eulerian-Lagrangian Technique
Authors: Datye Deepak V.
Published: January 2011

The penetration of spudcans in soil is associated with large plastic deformations of the soil. Finite element methods that are based on Lagrangian techniques often fail when large strain gradients in the soil lead to excessive distortions of the finite elements. Eulerian methods, on the other hand, allow material to flow across the finite element mesh and, hence, can be used to model such problems. In this work the Coupled Eulerian-Lagrangian technique, which is available in the Abaqus finite element code, has been used to model the penetration of spudcans in soil. The spudcan has been modeled as a Lagrangian body, and the soil as an Eulerian material that interacts with the Lagrangian body. Data on the resistance offered by the soil as the spudcan is uplifted, rotated, and moved horizontally are obtained. These resistance values can potentially be used as elastic-plastic joint stiffnesses in analyses in which the soil is not physically modeled.
Freak Waves Within the Third Order Model
Authors: Zheng Xiang Yuan , Moan Torgeir
Published: January 2011

After the New Year Wave was recorded in January 1995, considerable works have been devoted to explore the definition, physical nature and occurrence probability of freak waves. Within the frame of classical wave theories, the linear and 2nd-order random wave models have been chosen most often in the numerical simulations to study the occurrence of freak waves. This paper employs the 3rd-order random wave theory in simulation to investigate the effects of higher-order wave interaction on the freak wave occurrence. The New Year Wave is used as the case study herein. Its crest is 18.5 m, a criterion applied to categorize the simulated wave trains. To efficiently simulate a wave train with complicated wave interactions, a 1D FFT method is suggested. It is pointed out that the high values of skewness and kurtosis excess of New Year Wave cannot be captured by the 2nd-order model. The 2nd-order model is more suitable for reproducing events of high crests. Extreme events need a higher-order wave model. This work extends the study by Prevosto and Bouffandeau (2002). With totally 75,000,000 waves simulated the occurrences of freak waves of crest > 18.5 m are compared among linear, 2nd- and 3rd-order wave models. The comparative study also includes the predictions by Forristall (2000), Prevesto (2000) and the one derived based on Mori and Janssen (2004). The simulation once again reveals the inadequacy of the 2nd-order model to generate freak waves. The occurrence probability of freak waves under the 3rd-order model is more than 6 times higher than that under the 2nd-order.
Modelling the Effect of Sloshing on Ship Motions
Authors: Bunnik Tim , Veldman Arthur
Published: January 2011

Ships with partially filled liquid tanks, such as LNG carriers or FPSOs, are sensitive to sloshing in case they are exposed to waves. The effect of sloshing can have a pronounced effect on the ship motions, in particular roll in oblique seas. In this paper several methods are described which can be used to quantify this effect. The first is a linear diffraction method in which the effect of the liquid in the tank is modeled as a solid inertia of the fluid mass, an added mass and damping of the sloshing fluid and a hydrostatic free-surface correction to the GM. The response is easily computed in the frequency domain. The second is a time domain method in which the sloshing liquid in the tank is modeled with the CFD code ComFLOW. The forces exerted by the liquid on the tank walls are included in a time-domain simulation of the ship motions, based on linear potential flow for the outer domain (ship hull and ocean). The computed ship motions are again input for the motions of the liquid tank, generating a 2-way coupling between the dynamics of the tank and the ship. Both methods are applied to sloshing model tests, published by Molin (2008). In these tests, the response of a barge was measured with a completely filled and partially filled tank in beam seas. The results of the linear diffraction method agree reasonably well, but some differences in the roll response near the first sloshing mode are observed. The coupled time-domain method gives very good results for both low and high sea states.
Deepsea Pilot SMS Mining System for Harsh Environments
Authors: Espinasse Philippe
Published: January 2011

Following the trend of oil and gas production in deep waters, ore mining is about to start in the deep waters of the Pacific Ocean. If the first system will most probably be installed in the quiet though deep waters of Papua New Guinea, other prospects lie in the more turbulent areas of New Zealand and the Tongas. The ore accumulations to be mined are high grade hydrothermal mineral deposits rich in copper, gold, zinc, lead and silver located directly on the seabed. However, the excavation techniques need to be quite different from what had been envisaged for manganese nodules due to the morphology of the deposits. Based on its deep water construction experience, Genesis France, a company of the Technip Group has been contracted to perform a screening study of the various technologies to be applied to cut, crush, lift to the surface and pre-process the massive seabed sulphide deposits in a safe, efficient and profitable manner while minimizing the environmental impact of such work. This paper presents the conceptual screening study, the systems that have been evaluated, the selection criteria and the resulting operating system.
Practical Design Process for Flowlines With Lateral Buckling
Authors: Jin Joe , Audibert Jean M. , Kan Wan C.
Published: January 2011

In the past decade, lateral buckling has received growing attention in flowline design. Joint Industry Projects (JIPs) have led to publications of design guidelines, such as the SAFEBUCK design guideline and DNV recommended practice F110. Safe design of flowlines with lateral buckling involves complex considerations. Inadequate or late recognition of such complexities often results in major impacts on project execution. Experience gained in recent projects allowed us to improve the design process and design methods with incorporation of practical considerations. This paper presents three key aspects in developing robust flowline design with lateral buckling issues: 1) understand and reduce uncertainties in design basis for lateral buckling assessment, including operating conditions, characterization of geotechnical properties and flowline installation; 2) determine flowline-soil interactions with incorporation of field observations and engineering judgment; 3) manage impacts of lateral buckling through all project phases. This paper shares several key engineering considerations successfully used in recent flowline projects in deep waters where the seabed soil is characterized as soft clay. First, calculation of flowline embedment based on remolded shear strength instead of undrained shear strength eliminates the need to guess the embedment dynamic amplification factor. This approach is based on cyclic degradation of the soil shear strength and field observations. Second, a simple engineering model of axial resistance is proposed. The axial resistance is a cumulative behavior and hence only the average undrained shear strength is used for the calculation. Third, a robust engineering solution takes alignment in establishing quality design basis, engineering judgment to avoid unrealistic design load combinations, and trade-off among lateral buckling design effort, flowline construction and installation, and qualification of flowline capacities. And last, early recognition of lateral buckling issues and development of mitigation strategies are keys to project solutions. This paper also suggests that lateral buckling is very complex in reality and requires more investigations.
Average Flow Inside and Around Fish Cages With and Without Fouling in a Uniform Flow
Authors: Gansel Lars , McClimans Thomas A. , Myrhaug Dag
Published: January 2011

The average flow field inside and around the bottom of porous cylinders in a uniform flow is explored using Particle Image Velocimetry (PIV). Tests were conducted on six cylinders with porosities of 0%, 30%, 60%, 75%, 82% and 90% in a flume tank where the flow field inside and around the models is time averaged over 180 seconds. The models had a height-to-diameter ratio of 3 and were made from metal mesh. The Reynolds numbers ranged from 5,000 to 20,000 based on the diameter of the models and from 75 to 300 based on the diameter of individual strands of the mesh, which corresponds to the Reynolds numbers occurring at salmon fish cage netting used along the Norwegian coast. The porosities of 82%, 75% and 60% correspond to those of a fish cage netting in Norwegian Salmon farming with no, light and heavy biofouling, respectively. The results from this study are discussed with respect to the instantaneous flow field in and around the same cylinders at identical Reynolds numbers. The focus is on the effect of porosity on the ventilation inside the cages and the vertical transports within the near wake. It is shown that heavy fouling of aquacultural nettings can lead to internal circulation inside fish cages and therefore has the potential to reduce the ventilation of the net pens dramatically. The description of the time-averaged flow field inside and around porous cylinders can be used as benchmarks to validate and adjust numerical models of the flow past porous cylinders. The results from this study can be valuable also for the fish farming industry, as bio-fouling and the reduced porosity of fish cages can be monitored and controlled directly by fish farmers.
Warm Pipeline in Permafrost: A Sensitivity Study of the Major Thermal Properties
Authors: Xu Jianfeng , Eltaher Ayman , Jukes Paul
Published: January 2011

Pipelines carrying warm contents through permafrost areas present a key challenge to the development of petroleum reserves in the Arctic region. Evaluations have to be made during the pipeline design to avoid signification thaw settlement and large-scale permafrost damage. Current practice in estimating pipeline thaw settlement is primarily based on the assumption of a complete consolidation of the thaw-unstable layer. This often results in an over-conservative estimate and costly over-design. An integrated three-dimensional (3D) finite element (FE) model, developed recently as part of J P Kenny’s in-house simulator tools, has been used successfully to simulate the thermal and mechanical interaction between the pipeline and surrounding permafrost and gives a better estimate of the heat transfer, thaw settlement and pipeline deformation over the pipeline’s service life. Given the lack of experimental data and the complex nature of this problem, the sensitivity study on the major variables, presented in this paper and based on the 3D FE model, offers an in-depth insight into the problem and provides better-based guidelines for proper design of pipelines in permafrost. A number of thermal parameters are studied in this paper and compared based on their impact on the final deformation of the pipeline, so as to identify key parameters in the pipeline-permafrost thaw settlement processes. These parameters include the hydrocarbon content temperature and the convection coefficient, inside the pipe; the thickness and thermal conductivity of the insulation layer, on the pipe exterior; and the initial temperature, soil void ratio and the surface condition of the permafrost/soil, as boundary conditions. Results of current study improve the understanding of the pipeline-permafrost interaction from the heat transfer perspective and provide better guidance to the pipeline design in the permafrost environment.
Experimental and Numerical Study on Propulsive Performance of AUV
Authors: Suzuki Hiroyoshi , Inoue Tomoya , Watanabe Yoshitaka , Yoshida Hiroshi , Kitamoto Risa , Yamamichi Atsushi
Published: January 2011

Recently, several underwater vehicles (UVs) including autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs) have been developed. The purpose that such UVs are applied is various and the required performance for the UVs are also various. For example, they are oceanographic survey with long-distance cruising, plankton investigatory with high maneuverability and so on. Therefore, suitable UV for the mission is should be designed. In the above examples, UV that has the low resistance form is suitable for long-distance cruising; UV with low added mass form is suitable for plankton investigatory. Form the above viewpoint; we began working on a project to improve the UV’s hull form. Firstly, we focus on the resistance performance of UV within the resistance performance and maneuverability of UV. Using experimental and numerical methods, the relationship between the resistance performance and the UV’s hull form are investigated. In this paper, the part of the above results is introduced.
Thermal Protection and Microclimate of SOLAS Approved Lifeboats
Authors: Mak Lawrence , Kuczora Andrew , Farnworth Brian , Brown Rob , DuCharme Michel B.
Published: January 2011

Lifeboats are used as an evacuation system on a wide variety of offshore structures and marine vehicles. Currently, International Maritime Organization (IMO) Lifesaving Appliances (LSA) Code does not specify thermal protection and ventilation criteria for lifeboats. A test program was conducted to assess the system thermal protection and microclimate of SOLAS approved lifeboats for the Arctic environment. Some of the research findings of the first phase experiments are reported in this paper. In conducting experiments with a 72-person SOLAS approved lifeboat, the study found that the lifeboat only had a ventilation rate of 2 litres per second with vents open only, which may not be adequate. Inadequate ventilation will result in high concentration of carbon dioxide, causing headache, dizziness, restlessness, breathing difficulty, sweating, and increased heat rate, cardiac output and blood pressure. All of these may adversely affect lifeboat occupants in performing survival tasks. Using a thermal manikin, only slight decrease in thermal resistance (less than 10%) was observed in many test cases, when active ventilation was implemented (ventilation rate of 31 and 42 litres per second) and when side hatches were opened (ventilation rate of 95 litres per second). This suggests that reasonable increase in ventilation rate may be implemented without trading off much in thermal protection. However, a more noticeable decreases in thermal resistance (15% to over 30%) were observed when clothing was wet. This suggests it is critical to stay dry. A mathematical model was also developed to assess heat and cold stress of lifeboat occupants under different environment, lifeboat, occupant and ventilation conditions.