bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibration of Mobilized Soil Strength During Installation of Suction Piles
Authors: Burg E. C. , Frankl B. A. , Metz L. M. , Bang S.
Published: October 2008

An innovative breakwater system has been introduced for use in areas with thick soft seafloor, utilizing suction piles as the foundations. Gravity-type concrete caissons are placed on top, which resist the lateral loads caused by the wind and waves to protect the harbor behind. In Dec. 2004, four large concrete suction piles were prefabricated and installed successfully in southern Korea. During the installation of suction piles, detailed measurements were made on one pile, including the suction pressure vs. pile penetration relationship. They were used to estimate the mobilized soil strength during the suction pile installation. The calculated mobilized soil strength variation was then expressed as a function of a non-dimensional parameter that included the most essential parameters governing the behavior of suction piles during installation.
Dynamic Modeling of Deepwater Offshore Wind Turbine Structures in Gulf of Mexico Storm Conditions
Authors: Zambrano Thomas , MacCready Tyler , Kiceniuk Taras , Roddier Dominique G. , Cermelli Christian A.
Published: October 2008

A Fourier spectrum based model of Gulf of Mexico storm conditions is applied to a 6 degree of freedom analytic simulation of a moored, floating offshore structure fitted with three rotary wind turbines. The resulting heave, surge, and sway motions are calculated using a Newtonian Runge-Kutta method. The angular motions of pitch, roll, and yaw are also calculated in this time-domain progression. The forces due to wind, waves, and mooring line tension are predicted as a function of time over a 4000 second interval. The WAMIT program is used to develop the wave forces on the platform. A constant force coefficient is used to estimate wind turbine loads. A TIMEFLOAT computer code calculates the motion of the system based on the various forces on the structure and the system’s inertia.
A New Approach of Piping Dynamic Response Considering Plastic Effect
Authors: Yao Yanping , Lu Ming-Wan , Zhang Xiong
Published: October 2008

Dynamic response of piping system is significantly affected by plastic deformation. Based on the behavior classification of the pipe subjected to a steady axial force and a cyclic bending moment, the absorbed energy per semi-cycle due to plasticity is calculated for different elasto-plastic behavior. A new efficient piping dynamic response analysis method, plastic dissipation equivalent damping method, is proposed to consider the plastic effect on the basis of equivalence principle of energy dissipation. The proposed scheme is implemented in the finite element analysis code FEAP by introducing the equivalent damping which causes the same energy loss per semi-cycle. Numerical examples indicate that the results obtained by the present method show good agreements with those of elasto-plastic FEM analysis, and that this method can reduce the required computational effort significantly.
Numerical Modeling of Local Scour Below a Piggyback Pipeline in Currents
Authors: Zhao Ming , Cheng Liang
Published: October 2008

Local scour under two pipelines of different diameters in steady currents is investigated numerically. The two pipelines are arranged in the so-called piggyback configuration where the small pipeline is located directly above the large pipeline (as shown in Fig. 1). The Reynolds-averaged Navier-Stokes equations and the transport equation of the suspended sediment concentration are solved using a finite element method. The sediment mass conservation equation is solved for predicting the bed scour profile. The numerical model is firstly validated against the scour below a single pipeline where the experimental data are available. Then the model is employed to simulate the scour below two pipelines in steady currents. Computations are carried out for the diameter ratio (the small pipe diameter (d) to the larger one (D)) of 0.2 and the gap (G, between the two pipelines) to the large diameter ratio G/D ranging from 0.0 to 0.5. It is found that the flow and the scour profiles are influenced significantly by the gap ratio.
Simulation of Vortex Induced Vibration Around Offshore Pipeline
Authors: Bakhtiary Abbas Yeganeh , Ghaheri Abbas , Valipour Reza
Published: October 2008

The flow around a pipeline laid on the uneven seabed causes Vortex Induced Vibration (VIV), which in turn increases significantly the potential of fatigue damage of a pipeline at the free span sections. In general, the Morison equation is employed for estimating the averaged hydrodynamic force acting on an offshore structure; however, to elaborate the vibration forces due to VIV effects, simulation of vortex shedding and its induced time dependent pressure and velocity distribution is very essential. In this paper, it is intended to provide a numerical model to simulate the VIV effects on the offshore pipelines, by calculating numerically the vortex shedding and its induced turbulent pressure and velocity field. Finally, the unsteady pattern of dynamic drag force is obtained by the model, which is constructed based on the Reynolds Averaged Navier-Stokes (RANS) equations in conjunction with a standard k–ε turbulence model for turbulence closure.
A Reliability Assessment of Collapse Safety Factors for Tendon Design
Authors: Rinehart Adam J. , Buitrago Jaime
Published: October 2008

Since its first edition in 1987, the tendon system design section of The Recommended Practice for Planning, Designing, and Constructing of Tension Leg Platforms, API RP 2T, has not been materially revised. An entirely new draft of that section, including both strength and fatigue recommended practices, has now been completed. One key aspect for future designs is the maximum depth in which tendons can be installed while still maintaining adequate and consistent reliability. The new strength guidance recommends the axial tension-hydrostatic collapse interaction equation currently used by API RP 2A LRFD, coupled with a working stress design format with explicit tension and collapse safety factors. The latter factor controls the water depth applicability. To establish a basis for a hydrostatic collapse safety factor, ExxonMobil performed an independent reliability study to arrive at a safety factor consistent with the new interaction equation accuracy and current fabrication and design tendon practices. This paper presents the data gathering, analysis procedure, and interpretation of results leading to a safety factor that is consistent with standard practices. The analyses were conducted via Monte Carlo simulations for a number of design cases across a range of safety factors. Results indicate that a collapse safety factor of 1.67 for the Category A operational load case that controls tendon design in deep water yields levels of reliability consistent with those historically sought by design codes such as AISC and API.
Behaviors of a Very Large Floating Structure Supported With Dolphins Under Earthquake Loading: The Second Report — In Cases of Actual Earthquake Wave and Existence of Gaps Between Fenders and Dolphins
Authors: Watanabe Yoshiyasu
Published: October 2008

In recent years, tremendous research efforts have been directed toward developing very large floating structures (VLFSs) for the purposes of airports, terminals etc. on the sea to utilize ocean space. There is a VLFS which has a pontoon type structure supported with many dolphins and it is important to investigate sufficiently the behaviors of such VLFS under earthquake loading, because large reaction forces will be exerted on the dolphins and fenders that connect the dolphins and the floating structure. The preceding paper reported the behaviors of the floating structure, fenders and dolphins obtained from the time history response analyses of the structure with varying the period and velocity of the sinusoidal earthquake wave, when the horizontal rigidity of the floating structure was elastic and rigid and when the gaps between the fenders and dolphins were assumed to be zero. This paper reports, succeeding to the preceding paper, the results of the time history response analyses of a VLFS supported with 49 dolphins with varying the period and velocity of the applied actual earthquake wave in both cases where gaps between the fenders and dolphins are equal to zero and non-zero. In the analyses, the floating structure supported with dolphins is modeled as both a horizontally elastic and rigid plate supported with linear springs and dashpots through gap elements.
Forced Oscillation Experiments for VIV of Circular Cylinders and Behaviors of VIV and Lock-In Phenomenon
Authors: Masuda Koichi , Ikoma Tomoki , Kondo Norio , Maeda Hisaaki
Published: October 2008

This paper describes a model test to examine characteristics of vortex-induced vibrations (VIV) of tubing in water, e.g. a marine riser, and gives consideration of VIV characteristics from experimental results. Rigid circular cylinders are used for the model experiment because the authors assume that the model is a part of a marine riser. The test models are suspended into still water through a flat spring, and hence VIV can be found with hydroelasticity in spite of a rigid circular cylinder. This is a forced oscillation test in still water. The circular cylinders for the model test have drafts of 30cm, 60cm and 80cm, and diameter of 5cm and 8cm. The models are oscillated with periods of 0.5s to 4.6s and with about 7cm amplitude of the oscillation. In uniform flow, there is just one velocity of which flow causes the VIV lock-in. However, it is confirmed that there are several cases to experimental models, cases in which the VIV lock-in occurs in oscillatory flow. In addition, it is found that power spectra of VIV can be approximately classified into four patterns according to the number of spectral peaks and its property. Power spectra of VIV behavior from the model tests are compared with two-dimensional CFD computations.
A B-Spline Time Domain Solution for the Forward Speed Diffraction Problems
Authors: Datta Ranadev , Sen Debabrata
Published: October 2008

A B-spline based panel method is developed for the solution of the forward speed diffraction problem in time-domain. The body geometry is defined by an open uniform B-spline, and the unknown potentials and the source strengths are described by the same B-spline basis functions. The 3D potential flow boundary value problem is formulated based on a transient (time domain) Green’s function. Computed results are validated by comparing them with a wide variety of available results, including 3D numerical computations and experimental results. The present method agrees well with published results. Many of the existing 3D codes for the forward speed ship motion problem require high computing resources. The present method is however capable of producing the time simulation results over long duration using only a presently available PC, which is the main advantage of the proposed development.
Large Eddy Simulations of a Brine-Mixing Tank
Authors: Mousavi S. Mohammad , Zamankhan Piroz
Published: October 2008

Traditionally, solid-liquid mixing has always been regarded as an empirical technology with many aspects of mixing, dispersing and contacting where related to power draw. One important application of solid-liquid mixing is the preparation of brine from sodium formate. This material has been widely used as a drilling and completion fluid in challenging environments such as in the Barents Sea. In this paper large-eddy simulations, of a turbulent flow in a solid-liquid, baffled, cylindrical mixing vessel with a large number of solid particles, are performed to obtain insight into the fundamental aspects of a mixing tank. The impeller-induced flow at the blade tip radius is modeled by using the dynamic-mesh Lagrangian method. The simulations are four-way coupled, which implies that both solid-liquid and solid-solid interactions are taken into account. By employing a soft particle approach the normal and tangential forces are calculated acting on a particle due to viscoelastic contacts with other neighboring particles. The results show that the granulated form of sodium formate may provide a mixture that allows faster and easier preparation of formate brine in a mixing tank. In addition it is found that exceeding a critical size for grains phenomena, such as caking, can be prevented. The obtained numerical results suggest that by choosing appropriate parameters a mixture can be produced that remains free-flowing no matter how long it is stored before use.
Reliability Based Optimization of Submarine Pressure Hulls With Inelastic Interstiffener Buckling Failure
Authors: Radha P. , Rajagopalan K.
Published: October 2008

Uncertainties that exist in modelling and simulation, design variables and parameters, manufacturing processes etc., may lead to large variations in the performance characteristics of the system. Optimized deterministic designs determined without considering uncertainties can be unreliable and may lead to catastrophic failure of the structure being designed. Reliability based optimization (RBO) is a methodology that addresses these problems. In this paper the reliability based optimization of submarine pressure hulls in which the failure gets governed by inelastic interstiffener buckling has been described. The problem has been formulated to minimize the ratio of weight of shell-stiffener geometry to the weight of liquid displaced, subjected to reliability based inelastic interstiffener buckling constraint. Since the methods of analysis of inelastic buckling failure of submarine pressure hulls are inadequate, in the present study the Johnson-Ostenfeld inelastic correction method has been adopted for formulating the constraint. By considering spacing of the stiffener, thickness of the plating and depth of the stiffener as the design variables, Sequential Unconstrained Minimization Technique (SUMT) has been used to solve the design problem. RBO has been carried out to get the optimal values of these design variables for a target reliability index using Interior Penalty Function Method for which an efficient computer code in C++ has been developed.
Updated Design Procedure for Free Spanning Pipelines DNV-RP-F105: Multi-Mode Response
Authors: Fyrileiv Olav , Mo̸rk Kim , Chezhian Muthu , Sigurdsson Gudfinnur
Published: October 2008

In search for new gas and oil fields, the trend in offshore development points towards deeper waters, harsher environment, increased use of subsea installations and use of pipelines to transport the hydrocarbons to processing facilities onshore or in shallower waters. This also implies installation of pipelines at very uneven seabed causing a high number of spans that can be difficult and very costly to intervene. Conventional free span design according to the DNV Recommended Practice DNV-RP-F105 (2002) allows for vortex induced vibrations (VIV) as long as the integrity of the pipeline is within acceptable limits. However, the 2002 issue of the design code mainly covers short and moderate spans. As the knowledge about very long and/or multiple spans, where several vibration modes may be activated, has been limited, such cases have been treated in an assumed conservative way. This paper discusses the technical advancements in free span design in general and with respect to both long free spans and multi-spanning sections where several vibration modes may be activated simultaneously in particular. These advancements form the basis for the updated DNV-RP-F105 (2006). Changes from the former 2002 version are illustrated by an examples and the technical background is discussed.
Investigation of Constrained Viscoelastic Layers Efficiency to Increase Damping of Steel Risers Systems
Authors: Roitman Ney , de A. Pitella Bruno D. , Magluta Carlos
Published: October 2008

One of the most important problems in steel riser systems is the VIV phenomena (Vortex Induced Vibration), associated to high levels of structural vibration and stress concentration, and possible cause of considerable fatigue damage and reduction in lifespan. Based on constrained viscoelastic layers experience, a structural damping test was conducted on a representative model of steel riser in air with a damper mechanism application. It was done in an attempt to quantify and evaluate the damping coefficients. These structural damping tests were developed at the Structure Laboratory of COPPE/UFRJ, in Rio de Janeiro, Brazil. The test arrangement consisted of a vertically cantilevered pipe fixed at the base with the top end allowed to move freely. Two 18m long pipes, of 6-5/8in and 3in outer diameter, were used in the test to simulate single pipe and multi-pipe riser systems. Approximately 100 dynamics tests were satisfactory performed and the capability to reduce vibrations was clearly demonstrated. The experimental results obtained in the structural damping tests showed increases of 16 times for the new damping coefficients.
Implementation and Application of Modal Analysis During Time Domain Dynamic Simulation of Floating Offshore Systems
Authors: Correˆa Fabri´cio Nogueira , Jacob Breno Pinheiro
Published: October 2008

This paper presents the implementation and application of modal analysis during nonlinear time-domain dynamic simulations of floating offshore systems. The simulations are performed by a fully coupled nonlinear time-domain analysis methodology, which considers the interaction between the hydrodynamic behavior of the hull and the structural/hydrodynamic behavior of the mooring lines and risers. Considering the nonlinear variation of the stiffness and added mass of the floating system with time, the objective is to assess the variation of the natural periods of vibration for the 6-DOF of the floating system (surge, sway, heave, roll, pitch and yaw). To accomplish this goal, the generalized eigenvalue problem associated to the system is assembled, and the Generalized Jacobi Method is employed to solve this problem and determine natural periods of the system, at selected time intervals during the dynamic simulation. Case studies are selected to assess the variation with time of the natural periods, considering two different types of floating systems: the ITTC semi-submersible platform, for which experimental results are available; and a CALM monobuoy system. The results obtained stresses the importance of the calculation of natural periods in different positions of the system: due to the marked nonlinear behavior of the mooring lines and risers, the natural periods can show considerable variations, for instance, from the neutral design position to an equilibrium position under action of current.
Risk Based Inspection for Prioritizing Repair and Inspections of Large Numbers of Platforms in Gulf of Suez
Authors: El-Reedy Mohamed A.
Published: October 2008

GUPCO has more than hundred platforms located in Gulf of Suez that require topsides and underwater inspections on a regular basis as a part of integrity management system. Because of the high cost of underwater inspections and repair, GUPCO has developed a risk-based process to more effectively implement inspection resources. The process is based upon the critical key characteristics of each platform (year designed, number of legs, framing configuration, manning level, etc.) as well as results from previous inspections (date of last inspection, amount of inspection, flooded members, cut member, excessive marine growth, anode status, etc.). Using this information, the overall “risk” of the platform is determined using a rule-based scoring estimation of the likelihood and consequence of failure. In parallel, the severe damage platform structure is assessment by performing pushover analysis. The platforms are then ranked from highest to lowest risk, with the highest risk platforms receiving priority for repair and inspections. By calculating the likelihood of failure which is the main part of the assessment it is found that the age is the main factor affecting the structure condition. So from this paper one can calculate approximate value for failure likelihood occurring to the structure by knowing its age.
A Study on Structural Safety and Habitability of Superstructure Built on Floating Structure by Integration Analysis
Authors: Maruyoshi Koichi , Cho Yong-Soo , Song Hwa-Cheol , Saijo Osamu
Published: October 2008

The expectation of a floating structure for the ocean space utilization is increasing. In the future, when a floating structure will be used as the ocean space utilization, buildings will be constructed on a floating structure and people will be active at the building. The building is called superstructure in this paper. A superstructure is deformed by wave loads unlike the land buildings. For the purpose, it is necessary that the dynamic characteristics of a superstructure due to wave loads are grasped. The superstructure should be safe and comfortable for people. Therefore a superstructure must satisfy the requirements for the structural safety and the habitability in the step of the primary design. In this paper, the response of a superstructure is carried out by integrated analysis. The significant waves for 100 year return period and those for 10 year return period are used for the confirmation and the evaluation of the structural safety and the habitability respectively. The results on the structural safety and the habitability are discussed.
Time-Variant Reliability Assessment of FPSO Considering Corrosion and Collision
Authors: Zhang Daokun , Tang Wenyong , Zhang Shengkun
Published: October 2008

Floating production, storage, and offloading (FPSO) system has been widely used in the offshore oil and gas exploitations. Since it has long intervals of docking for thorough inspection and maintenance, and is exposed to collision risk at sea, the time-variant reliability of FPSO becomes very important as for the risks of corrosion and collision. The corrosion defect is modeled as the exponential function of time. The Idealized Structural Unit Method is also proposed to predict ultimate strength of hull girder. Still water and wave-induced bending moments are also combined into stochastic processes. Reliabilities of intact hull during the service are calculated as references to those of collided hulls with effect of corrosion defect. Collision condition is a focus in this paper, where collided hulls are modeled according to ABS instructions. According to the instructions, the section with highest bending moment, which almost locates at the mid ship, should be noticed. Therefore still water bending moments of mid section of collided hulls are achieved and divided into two groups based on collision positions. One is that the mid section is broken, which is named as “direct damage”. Another is that other else section is broken, which is named as “influence”. Result shows that “influence” condition has higher still water bending moment than “direct damage”, which is usually neglected in previous researches. Finally, reliabilities of collided hulls throughout the service life are obtained, which can become references to further inspection and maintenance plan.
Fatigue Damage at the Root of the Gate Lip of the Water Gate Under Variable Water Pressure Due to Tide and Ocean Wave
Authors: Konuma Keitaro , Toyosada Masahiro , Gotoh Koji
Published: October 2008

The steel water gate, which received variable water pressure due to gap of water level between sea and balancing reservoir, damaged in its gate lip by fatigue crack. In order to find the cause of this damage, various investigate programs, including observation with microscope and measurement of stress and water level, were performed. By the comprehensive analysis of the results of these investigation programs, it was concluded that this damage was caused by the cyclic loading on the gate lip from the ground surface, and found out the relation between sea water level and stress occur at damaged point. After then, the damaged part was replaced with new reinforced element. In addition, for checking the effect of this measure, the crack growth estimation was executed with FLARP, the numerical simulation code which was developed by the authors. As the result of the numerical simulation, the crack growth curve became visible quantitatively, and it was confirmed that the possibility of the reoccurrence of the fatigue crack was removed by the measures which we took, under the assumed loading condition.
Burst Tests on Pipeline Containing Closely Spaced Corrosion Defects
Authors: Benjamin Adilson C. , Freire Jose Luiz F. , Vieira Ronaldo D. , de Andrade Edmundo Q.
Published: October 2008

In this paper the burst tests of five tubular specimens are presented. In these tests the tubular specimens were loaded with internal pressure only. The specimens were cut from a longitudinal welded tube made of API 5L X80 steel with a nominal outside diameter of 457.2 mm (18 in) and a nominal wall thickness of 7.93 mm (0.312 in). The specimen IDTS 8 contains only one defect, herein called base defect. The base defect is an external flat bottomed defect with uniform width (circumferential dimension). The other four specimens contain groups of interacting defects constituted by the combination of three or more base defects. All the defects were machined using spark erosion. Measurements were carried out in order to determine the actual dimensions of each tubular specimen and its respective groups of defects. Tensile specimens and impact test specimens were tested to determine material properties. The failure pressures measured in the laboratory tests are compared with those predicted by five assessments methods, namely: the ASME B31G method, the RSTRENG 085dL method, the DNV RP-F101 method for single defects, the RPA method and the RSTRENG Effective Area method.
Effect of Current on Flexural Gravity Waves
Authors: Bhattacharjee Joydip , Sahoo Trilochan
Published: October 2008

The effect of uniform current on the propagation of flexural gravity waves due to a floating ice sheet is analyzed in two dimensions. The problem is formulated as an initial boundary value problem in the linearized theory of water waves. By using Laplace transform technique, the initial boundary value problem is reduced to a boundary value problem, which is solved by the application of Fourier transform to obtain the surface elevation in terms of an integral, which is evaluated asymptotically for large distance and time by the application of method of stationary phase to obtain the far field behavior of the progressive waves. The effect of current on the wavelength, phase velocity and group velocity of the flexural gravity waves propagating below the floating ice sheet is analyzed theoretically to obtain certain critical values on the speed of current which are of significant importance. Simple numerical computations are performed to observe the effect of uniform current on the surface elevation, wavelength, phase velocity and group velocity of flexural gravity waves and on the far field behavior of the progressive waves.
Numerical Prediction of Impact-Related Wave Loads on Ships
Authors: Schellin Thomas E. , El Moctar Ould
Published: October 2008

We present a numerical procedure to predict impact-related wave-induced (slamming) loads on ships. The procedure was applied to predict slamming loads on two ships that feature a flared bow with a pronounced bulb, hull shapes typical of modern offshore supply vessels. The procedure used a chain of seakeeping codes. First, a linear Green function panel code computed ship responses in unit amplitude regular waves. Wave frequency and wave heading were systematically varied to cover all possible combinations likely to cause slamming. Regular design waves were selected on the basis of maximum magnitudes of relative normal velocity between ship critical areas and wave, averaged over the critical areas. Second, a nonlinear strip theory seakeeping code determined ship motions under design wave conditions, thereby accounting for the ship’s forward speed, the swell-up of water in finite amplitude waves, as well as the ship’s wake that influences the wave elevation around the ship. Third, these nonlinearly computed ship motions constituted part of the input for a Reynolds-averaged Navier-Stokes equations (RANSE) code that was used to obtain slamming loads. Favourable comparison with available model test data validated the procedure and demonstrated its capability to predict slamming loads suitable for design of ship structures.
Non-Linear Fatigue Analysis for Jacket Offshore Structures
Authors: Gaidai O. , Naess A.
Published: October 2008

This paper presents different approaches for accounting for nonlinear effects in fatigue analysis. One approach is an application of the quadratic approximation method described in [3, 4] to the stochastic fatigue estimation of jacket type offshore structures. An alternative method proposed is based on a spectral approximation, and this approximation turns out to be quite accurate and computationally simple. The stress cycles causing structural fatigue are considered to be directly related to the horizontal excursions of the fixed offshore structure in random seas. Besides inertia forces, it is important to study the effect of the nonlinear Morison type drag forces. Since no direct method for dynamic analysis with Morison type forces is available, it is a goal to find an accurate approximation, allowing efficient dynamic analysis. This has implications for long term fatigue analysis, which is an important issue for design of offshore structures.
Investigations on the Fluid-Structure Interactions of Fishing Nets
Authors: Winkel Hans-Joachim , Paschen Mathias
Published: October 2008

Modern nets consist of meshes made of threads or twines with spirals or helical strakes. Fluid-structure interactions have been investigated in Rostock for a long time applying different theoretical models. Because of great net flexibility there is a need of calculation methods which consider the main physical qualities. This is done by the approximation of wake of threads by results from circular cylinders and influence of circulation, which is known from measurements of transverse force. Results of measurements with two models with and without spirals are given for comparison.
Spar Deck Float-Over Feasibility Study for West Africa Environment Condition
Authors: Ji Chunqun , Halkyard John
Published: October 2008

Offshore deck installation may be performed by either derrick barges or by the float-over method. Either method involves a variety of technical challenges. The challenges are particularly severe in weather conditions such as West Africa where long period swell dominates the environment. Setting a deck on a floating platform such as a spar presents additional issues compared with operation on fixed platform. This paper provides a spar deck float-over feasibility study for a West Africa environmental condition. The design uses two existing barges in a catamaran configuration. The barges were engaged for both transportation and the float-over procedures. The weather window for spar deck installation and the importance of synchronized motion of spar, barge and deck during the deck load transfer are discussed in the paper. Four-body (two barge, spar and deck) motion simulations were applied. The study shows that the float-over and mating operation is feasible in the specified West African sea state. Rapid spar de-ballasting achieves 20% load transfer to avoid large impact during 0% to 20% load transfer. From the 20% to 85% deck load transfer using conventional ballasting the barges, deck and de-ballasting spar will have synchronized motion.
Free Surface Viscous Flow Around a Ship Model
Authors: Wanderley Juan B. V. , Levi Carlos
Published: October 2008

The present stage of viscous flow numerical analysis combined with computer technology latest advances made viable the mathematical treatment of many robust and complex engineering problems of practical interest. Some numerical problems which solutions would be just unthinkable not more than ten years ago may be now dealt with in a reliable and fairly accurate manner. A truly example of this kind of problem would be the calculation of hydrodynamic loads acting on yawing ships. The solution of such a problem raises practical interest due to applications, for instance, as in the case of stationary FPSO/FSO ships facing sea currents, commonly used in offshore deep-water oil production. In the present solution, the complete incompressible Navier–Stokes (N-S) equations are solved by means of an algorithm that applies the Beam and Warming [1] approximated factorization scheme to simulate the flow around a Wigley’s hull. The numerical code was implemented using 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 and high efficiency of the algorithm indicated its potential to be used as an effective tool in ship design.
Numerical Simulation of Roll Damping
Authors: Wanderley Juan B. V. , Ramiro Andre´ , Reis Thiago , Fernandes Antonio Carlos , Levi Carlos
Published: October 2008

The highly viscous flow problem of roll damping of a FPSO is investigated by means of numerical solution of the unsteady two-dimensional Navier-Stokes equations. The finite volume method using non-structured grid is used to solve the integral form of the governing equations. The cross section of the FPSO hull with an initial roll displacement is let free to oscillate in roll in an initially still fluid. The numerical simulation provides a realistic picture of the physics of the phenomenon, capturing the vortex formation around the bilge keel. Numerical results from roll free decay tests are compared with experimental data showing a fairly good qualitative and quantitative agreement of the roll damping.
Performance Prediction of Planing Hulls With Propeller Tunnels
Authors: Subramanyam P. V. V. , Subramanian V. Anantha
Published: October 2008

In order to study the performance of planing hulls with propeller tunnels, the resistance tests have been conducted on two models with and without tunnels in a towing tank for different forward speeds in calm water condition. Two models were provided with tunnels of different tunnel area ratios (The ratio of projected area of tunnels to the projected water-plane area of the model) of 0.07 and 0.12 by keeping the propeller immersion constant. Wetted surface area, trim angle and CG rise were measured at three different drafts as a part of the study. Pressure measurements were also conducted for a chosen case for a design draft. The extrapolation of resistance from model to prototype has been done using modified Froude’s extrapolation method, which takes the average bottom velocity and trim angle into account. The resistance was also calculated using the method given by Savitsky (1964). The results show that the resistance of the model with tunnel is less when compared to that without tunnel for the same model irrespective of the drafts in case of the model with larger tunnel area ratio. Such variation was not exhibited in the case of the model with lesser tunnel area ratio. Hence, it is observed that the model having the larger tunnel area ratio has beneficial effect due to tunnels. The Savitsky method based results have been compared with experimental results. Pressure distribution along the length of the model shows that the maximum pressure peaks occur near the forward region and reduces towards aft with undulations.
Applications of a Compound Distribution on Estimating Wind and Wave Parameters for Fixed Platforms Design
Authors: Dong Sheng , Ning Jinjin
Published: October 2008

Based on the hindcast data of 21 storm processes, a Poisson bivariate Logistic extreme value distribution is proposed to estimate the joint probability of extreme wind speed and extreme significant wave height in the storms, the frequency of which can be described by a Poisson distribution. In order to calculate the structural response of an ocean platform, such as base shear, three methods are utilized, namely (I) traditional univariate frequency analysis method; (II) base shear return value method; (III) wind-wave joint probability method. Calculation results show that the proposed statistical model is suitable for the design of fixed platforms in the storm-influenced area.
Underwater Long-Term Observation at the Largest German Artificial Reef in the Baltic Sea
Authors: Niedzwiedz Gerd
Published: October 2008

The Baltic Sea is one of the most frequented regions in the world. The Baltic neighbouring states more and more see the need to adapt their economic interests to the given ecological conditions. This can not always be done sufficiently, which can be seen at the example of coastal fishery in some of these countries. Owing to the critical condition of economically important fish stocks, selective fishing and fish-stock saving measures have become main fields of research. Supported by the European Union and by the federal state government we have tried in Mecklenburg-Vorpommern during the last four years to investigate the effects of an artificial Baltic reef with respect to fishing. For this purpose more than 1300 reef elements — made of a special sort of concrete and having different shapes and size — have been arranged on an area of 200 × 200 m at a water depth of 12 m about 1.5 m away from the coast. Over a period of almost four years different methods and techniques have been applied to observe and record the effects of these structures on the natural environment in a long-term investigation. Continuous video-optical underwater observation using up to nine simultaneously controlled underwater cameras proved to be a special technical challenge. Important results have been gained from a monitoring with research divers and from a defined test and comparison fishing done once every month. Various fishing methods have been applied — also those which are normally not common in that region. A special low-cost variant of a remote controlled underwater stereo photo camera has been developed and built in order to get biometric data of the fish without catching it.
Influence of Axial Force on the Vibration of Euler-Bernoulli Beam Structures Solved by DQEM Using EDQ
Authors: Chen Chang-New
Published: October 2008

The influence of axial force on the vibration 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 eigenvalue 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.
Research Into the Extraction of the Appeal Points of Marine Space in the Okinawa Marine Resort and a Method of Estimating the Accommodated Population
Authors: Miyazaki Wataru , Kondo Takeo , Yamamoto Kazukiyo , Ootuka Motohisa , Takahashi Hideki , Miyazaki Hitosi
Published: October 2008

In the formation of a marine resort, the extraction of the various appeal points of marine space is an important issue. For this reason, this research project targeted Kumejima in Okinawa Prefecture, Japan, and considering tourists who visit the resort as the target of the study, a decision was taken to evaluate the quality of the appeal points that comprise the resort. As a result, the appeal points of marine space were found to be comprised of three main resource elements and 13 categories related to these elements. The accurate number of tourists who visit a resort, be it marine resort or otherwise, must be grasped in order to plan the promotion of the resort and reactivation of the community. For this reason, this research project proposed a method of grasping such trends utilizing tobacco tax that is a unique system of taxation in Japan. As a result, time and cost were conserved compared to past methods and it was possible to grasp the annual number of tourists with high precision. Based on these results, it is believed that materials that indicate the direction of the formation of marine resort in Kumejima in the future have been provided.
A Lagrangian Two-Phase Model for Assessing the Near-Field Impacts of CO2 Ocean Sequestration
Authors: Chen Baixin , Nishio Masahiro , Song Yongchen , Akai Makoto
Published: October 2008

A new version of a two-phase numerical model is developed to simulate CO2 droplet dissolution and the plume dynamics of CO2 enriched seawater produced by direct release of liquid CO2 into deep ocean from a towed pipe. This Lagrangian framework model consists of three sub-models. They are the CO2 droplet moving and dissolving sub-model, the turbulent dispersion of CO2 enriched seawater sub-model, and the biological impact sub-model. We performed simulations of direct injection of liquid CO2 from a release platform towed by a moving-ship into mid-depth seawater to examine the roles of injection parameters, including release platform type and initial CO2 droplet size. Results from the simulations show that a horizontal release platform can create a plume with less physical and biological impacts than a plume created by a vertical release platform. With an injection rate of 100kg/s, simulations predict that injection of small droplets (5mm in diameter) would produce up to 1.5 times the pH reduction of larger droplets (15 mm in diameter). This large pH reduction may significantly affect ambient zooplankton.
Time Histories of Wave-in-Deck Loading on Jacket Decks
Authors: van Raaij Katrine , Gudmestad Ove T.
Published: October 2008

Most researchers agree that wave-in-deck loading is of dynamic nature and that the dynamic effects on the structural response are important. However, there exists no engineering practice for the determination of load time histories for waves hitting the decks of fixed offshore platforms. This applies to both the time variation and the magnitude of the loading. This paper presents the main recommendations for wave-in-deck loading with reference to wave tank experiments of a model of the Statfjord A Condeep platform subjected to extreme wave loading. The recommendations for loading from these tests comprise time variation as well as magnitude. These recommendations are used as a basis to suggest a simplified method to estimate wave-in-deck loading on jacket platform decks, for which, to the difference from Condeep platforms, the wave height amplification due to the interaction between the incoming wave and the structure (Swan et al., 1997) is negligible. The resulting ‘recipe’ for wave-in-deck time histories on North Sea jacket platforms is compared to relevant results previously reported in the literature. The method is categorised as a ‘global’ approach, that is, one uses an effective deck area as opposed to a detailed deck model. The method is suggested to be applicable for analyses where a ‘rough but reasonable’ estimate for wave-in-deck loading is sufficient.
Full-Scale Measurements on Hull Response of a Large-Container Ship in Service
Authors: Miyahara Kenichiro , Miyake Ryuju , Abe Norikazu , Kumano Atsushi , Toyoda Masanobu , Nakajima Yoshiyuki
Published: October 2008

In order to investigate hull responses of post-Panamax container ships in the actual sea, full-scale measurements on hull responses of a post-Panamax container ship in service were conducted. In linear wave domain, the probability density distributions of hull responses obtained by full-scale measurements were compared with the Rayleigh distributions to check on the range of the applicability, and comparisons with the long-term distributions of the longitudinal stress obtained by full-scale measurements and the direct structural analyses based on the wave loads analyzed by using the linear 3D Rankine source method were made to verify the accuracy. In non-linear wave domain, the measured longitudinal stresses showed the asymmetry of vertical bending moment. The long-term distributions of hull responses, which have the high harmonic components, obtained by full-scale measurements were compared with the numerical results analyzed by using non-linear methods to investigate the non-linearity on hull responses of container ship.
Numerical and Experimental Study of 3-D Sloshing in Tanks of LNG Carriers
Authors: Arai Makoto , Makiyama Humberto S. , Cheng Liang-Yee , Kumano Atsushi , Ando Takahiro , Imakita Akihiko
Published: October 2008

This paper describes a numerical analysis of sloshing in liquid cargo tanks of membrane-type liquefied natural gas (LNG) carriers in a rough sea. The numerical method used in this study is based on a finite-difference method, in which impact pressure on the tank ceiling is treated accurately by a numerical boundary condition proposed by the authors. Tank motion with six degrees of freedom was given by the response amplitude operator of a ship, and sloshing that occurs in regular and irregular waves is examined. An ISSC wave spectrum is used to generate the irregular waves. We describe the influence of 3D effects due to tank motion and tank geometry on the sloshing flow, and show the strong relation of the sloshing to the frequency of the given ship motion. Comparison of the numerical results with the measured data shows the effectiveness of the presented 3D analysis method.
Computational and Experimental Simulation of Nonbreaking and Breaking Waves for the Investigation of Structural Loads and Motions
Authors: Clauss Gu¨nther F. , Stu¨ck Robert , Stempinski Florian , Schmittner Christian E.
Published: October 2008

For the analysis of loads and motions of marine structures in harsh seaways precise information about the hydrodynamics of waves is required. While the surface motion of waves can easily be measured in physical wave tanks other critical characteristics such as the instantaneous particle velocity and acceleration as well as the pressure field, especially under the wave crest are difficult and time-consuming to obtain. Therefore a new method is presented to approximate the wave potential of a given instantaneous wave contour. Numerical methods — so called numerical wave tanks (NWTs) — are developed to provide the desired insight into wave hydrodynamics. A potential theory method based on the Finite Element method (Pot/FE), a RANSE (Reynolds-Averaged Navier-Stokes Equations) method applying VOF (Volume of Fluid) and a combination of both is utilized for the simulation of different model wave trains. The coupling of both CFD (computational fluid dynamics) solvers is a useful approach to benefit from the advantages of the two different methods: The Pot/FE solver WAVETUB (wave simulation code developed at Technical University Berlin) allows a very fast and accurate simulation of the propagation of nonbreaking waves while the RANSE/VOF solver has the capability of simulating breaking waves. Two different breaking criteria for the detection of wave breaking are implemented in WAVETUB for triggering the automated coupling process by data transfer at the interface. It is shown that an efficient method for the simulation of breaking wave trains including wave-structure interaction in 2D and 3D is established by the coupling of both CFD codes. All results are discussed in detail.