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to

GoAn obvious objective of this paper is to examine the effectiveness of reducing the lateral vibration of a jacket offshore platform by means of improving the layered soft soil. Soil reactions on a unit length pile are described by dynamic Winkler spring coupled dashpot. Based on the PSD of the deck displacement, amplitude frequency response and the time histories response, the influence of the soil properties on the vibration properties of the platform are analyzed.

Pile foundations are extensively used to support offshore and onshore structures. The super-structure forms an integral part of the pile-foundation system. Very little information is available on the behavior and analyses of the total system (Prakash et al, 1992). Fixed jacket platforms are most prolific and prevalent in the offshore industry today. Under dynamic excitations due to earthquake, wind, operation of machines and wave attack, offshore structures are unceasingly, therefore, an analysis of the lateral vibration properties of the jacket platforms system are desirable. The jacket platforms addressed in this paper is a living one located at a mean water depth d=11.2m of BoHai.

ISOPE-I-02-011

The Twelfth International Offshore and Polar Engineering Conference

For the global and fatigue structural strength analysis of a semisubmersible platform, the wave loads of design conditions are calculated by using the three-dimensional boundary element method. The maximum of vertical bending moment, torsion moment and horizontal split force are determined from a serious of design waves with limited wave periods and positions of incident wave crest, indicated by the wave phase from 0° to 360° in one wave period. The extreme wave loads under the combination of wave parameters and the transfer functions of wave loads are used as the input of hydrodynamic pressure in the three-dimensional FEM analysis process.

In the practice of engineering design for ships and ocean structures the direct calculation procedure is wildly applied in structure verification, in which the three-dimensional FEM analysis is used more and more commonly. The hydrodynamic pressure distribution on hull surface induced by waves is the dominant component of the input loads of the FEM analysis. Ordinary three methods are used in the calculation of hydrodynamic pressure: the Morison formula method, the strip method and the three-dimensional panel method. Considering complex structure and large scale for the semi-submersible platform, the panel method is used in this computation. To assume the fluid is irrotational, the problem of prediction for the motions and loads of floating body in waves can be expressed in the form of Laplace''s equation with propriety boundary conditions. For the frequency domain, the evaluation of Green function without forward speed is well discussed by Newman(1985) and Stergios(1992). The evaluation of Green function of the translating and pulsating source is much more complex because of a double integral. Zong and Huang(199l) give a form of single integral for this function but the kernel function is oscillated in some parts of integral field.

ISOPE-I-02-324

The Twelfth International Offshore and Polar Engineering Conference

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (0.89)

A new Office of Naval Research program is focusing research on processes associated with the burial of mines in shallow water. Liquefaction due to surface waves, and possibly due to other loadings such as the rocking of mines due to hydrodynamic loads, constitutes one of the potentially important mechanisms responsible for the sinking of mines in certain environments. The basic equations required for a quasi-static modeling approach are reviewed and finite element predictions are presented for the case of ‘momentary’ liquefaction associated with surface water waves. The predictions are shown to match the corresponding analytical expression remarkably well, which lends confidence to the overall numerical methodology.

The accurate prediction of mine burial in shallow water is one of the most urgent needs of United States and North Atlantic Treaty Organization (NATO) naval forces (Brown and Foxwell, 1991; Tusa, 1991; Richardson and Tooma, 1993). Current mine counter-measures (MCM) are hampered by a lack of robust burial models. For the most part, existing algorithms were developed some two to three decades ago and do not incorporate the scientific progress that has been made since in modeling and testing (Brandes, 1999). For example, the current mine burial prediction model in use by United States MCM forces relies on crude seafloor maps that classify the seabed into a few soil types based on overall gradation, i.e. clay/silt, sandy, and rocky bottoms. Other than texture, the potential for mine burial is assessed by very crude penetration resistance measurements conducted by divers who punch the seabed with their fists and report the amount of penetration in ‘arm lengths’. The current model is an ‘impact’ model that attempts to estimate the amount of burial upon mine placement but does not attempt to make any predictions as to time-dependent burial.

ISOPE-I-02-220

The Twelfth International Offshore and Polar Engineering Conference

burial, condition, consolidation, earthquake loading, equation, excess pore, liquefaction, model, Offshore, prediction, Reservoir Characterization, reservoir description and dynamics, sediment, seismic processing and interpretation, stress, surface, surface water wave, surface wave, Upstream Oil & Gas, water, Wave

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.35)

Matsunaga, Nobuhiro L. (Dept. of Environmental Fluid Science & Technology, Kyushu University) | Hashida, Misao (Dept. of Civil Engineering, Nippon Bunri University) | Uzaki, Ken-ichi (Dept. of Earth System Science & Technology, Kyushu University) | Uragami, Yukiko (Dept. of Earth System Science & Technology, Kyushu University) | Kanzaki, Takayuki (Saiki Iron and Steel Industry Cooperation)

A new type of steel floating breakwater, which is comprised of a boxtype pontoon and truss structure, was designed for incident waves to be broken efficiently by the front truss and for the pontoon to suppress the transmission of the small broken waves. The performance of wave absorption is investigated by changing systematically the experimental parameters and the dimension of the floating breakwater. The transmission coefficients are normalized by introducing a representative dimensionless parameter, and a universal expression for the transmission coefficients is obtained. The relationships between the introduced representative parameters and the dimension of the breakwater or the wave parameters are investigated with the aid of a dimensional analysis. The universal expression for the transmission coefficients and the quantification of the representative parameter enable us to estimate the transmission coefficients of the steel floating breakwater constructed in an arbitrary sea area.

The construction of floating breakwaters is restricted in relatively calm sea areas, because the performance of wave absorption lowers rapidly as incident waves become bigger and they are much weaker than gravity-type breakwaters. However, they have some advantages, e.g., the performance of wave absorption is not influenced by the change of sea level, seawater exchange and fish migration are not hampered so much, their construction is not influenced by sea-bed conditions and so on (see Sorensen (1997)). Therefore, various kinds of floating breakwaters have been developed and used widely to control the waves coming into small sea areas of fishing ports, fish farms, marine resorts, etc. Sorensen(1997) reviewed three types of floating breakwaters as common ones in his text book, i.e., prism, catamaran and flexible structures, and gave the relationships between their transmission coefficients and the ratios of the width of the structures to the wavelength of incident waves.

ISOPE-I-02-377

The Twelfth International Offshore and Polar Engineering Conference

From a view of fatigue strength, a critical review on thermo-mechanically controlled process (TMCP) steel was shown with picking up comparative test results in the past on fatigue strength for TMCP steels, including welded joint, to that of conventionally rolled plates and with introducing key experiments about important effect of softened HAZ on welded joint fatigue behaviors, for the purpose to bring greater attention for structure designer to obtain maximum advantages of TMCP steels such as excellent weldability, high toughness at HAZ and good performance in cost efficiency.

At present TMCP steels are widely used in large-size welded structures. With comparing to conventionally rolled steel, TMCP steels has strong advantages such as better weldability and high toughness at heat affected zone (HAZ), that means with no preheating to heavy welding and reduced weld cracking at HAZ etc.. On the other hand, combination of low carbon equivalent and large heat input welding may result in softened HAZ growth, of which tensile strength is lower than that of the base metal so that it could reduce the welded joint strength locally. There are several types of TMCP plates, say accelerated water cooling type (Type-III) and non-water cooling type (Type-I and –II), and being low carbon equivalent is a common feature to all the types of TMCP steels. So that the effect of softened HAZ on the weldment strength had been an issue of wide importance to make clear and hence many studies and tests have done on the subject in Japan. In this paper from the viewpoint of fatigue, results of critical review will be shown on the past comparative fatigue tests on TMCP steels to conventionally rolled plates and the key experiments that deal with the effect of softened HAZ on the welded joint fatigue behavior.

ISOPE-I-02-449

The Twelfth International Offshore and Polar Engineering Conference

Kinoshita, Takeshi (Institute of Industrial Science, University of Tokyo) | Bao, Weiguang J. (Institute of Industrial Science, University of Tokyo) | Yoshida, Motoki (Institute of Industrial Science, University of Tokyo) | Ishibashi, Kazuko (Institute of Industrial Science, University of Tokyo)

When a body is slowly oscillating in waves, there exists another source of added mass and damping, i.e. the so-called wave drift added mass and wave drift damping. They are resulted from the nonlinear interaction between the slow oscillations and the waves. Different from the conventional added mass and wave-radiating damping, they are quadratic forces in wave amplitude. The wave drift added mass is measured in the present work from a free decay test or a forced slow oscillation test. The model is either a circular cylinder or an array of four circular cylinders. Experimental parameters are systematically changed to examine their effects on the wave drift added mass. A calculation based on the potential theory is also carried out.

Ocean structures are usually constrained by mooring systems, which supply relatively weak restoring forces in horizontal plane. Under the slowly varying drift forces exerted by ocean waves, these structures may undergo low-frequency resonant oscillations in the horizontal motion modes, i.e. surge, sway and yaw. Conventional added mass and damping can be obtained by solving a linear radiation problem in which the body of the structures is forced to oscillate in the calm water. In the case when the frequency of the resonant motion is very small, the wave-radiation damping is negligibly small, while the added mass is the same order of the displaced water mass. However, with the presence of the incident waves, there exists another kind of added mass and damping that is caused by the nonlinear interaction between waves and slow oscillations. As part of the nonlinear wave loads, their magnitude is proportional to the square of the wave amplitude, which is different from the conventional added mass and damping, and they are called wave drift added mass and wave drift damping respectively.

ISOPE-I-02-321

The Twelfth International Offshore and Polar Engineering Conference

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.48)

Prediction of smoke flow movements in marine and offshore compartment fires is still a challenging work for fire safe researchers. The research described in this paper is an effort to apply the computational fluid dynamics (CFD) model to numerically simulate such smoke flows. The present computation model involves a CFD code to solve three-dimensional turbulent buoyancy-driven flows using a set of low-Mach-number approximated governing equations, a turbulence model based on large eddy simulation, and a combustion model to calculate the heat release rate from fires. A pool fire is simulated and the results are compared to measured data of a laboratory experiment. A simulation of an engine room fire of a coastal LPG ship is also presented as an example of applications.

For most of recorded maritime history, fire has been a major cause of loss of ships and offshore platforms. To design a fire safety system for a ship or an offshore platform is therefore one of the most important problems for the functional designers. There have been a number of studies attempting to model fire phenomena, and a newest review is provided by Tieszen (2001). The zone models, in which room averaged quantities are predicted for multi-room problems, have been used extensively for engineering applications. Recently, field models, which make the simulation possible in much finer spatial and temporal resolution, are used in the study of fires. The research described in this paper is about a field modeling approach, which is being under development. A distinguishing feature of the fire problem is that the temperature difference as well as the density variation is very large while the speed of the smoke flow induced by the heat release is much slower than that of the propagation of acoustic waves.

ISOPE-I-02-460

The Twelfth International Offshore and Polar Engineering Conference

A statistical model is developed to predict wave overtopping of extreme waves on a fixed deck. The probability density function for the volume of overtopping water is based on the truncated Weibull distribution with the assumption of local sinusoidal wave profile. Sensitivity to the wave nonlinearity parameter and deck clearance are discussed. The statistical model is compared to laboratory data of the instantaneous free surface elevation measured in front of a fixed deck and the instantaneous free surface elevation and overtopping rate measured at the leading edge of the deck. The statistical theory compared well with the measured exceedance probability seaward of the deck. Conditional sampling of the crest heights seaward of the deck gave a normalized probability distribution similar to that of the maximum water level measured on the deck for each overtopping event. The model prediction of the exceedance probability of deck overtopping gave very good agreement for large overtopping values.

Many offshore platforms have suffered from significant wave loading on their lower deck (Bea et al. 1999), and floating production storage and offloading (FPSOs) systems have also suffered topside damage from “green water” on their decks during storms (

ISOPE-I-02-298

The Twelfth International Offshore and Polar Engineering Conference

amplitude, Artificial Intelligence, assumption, case, crest, deck, distribution, elevation, exceedance probability, exp, floating production system, incident wave, probability, Rayleigh, Rayleigh distribution, rayleigh weibull, statistics, subsea system, Upstream Oil & Gas, Wave, wave crest, Weibull, Weibull distribution

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Floating production systems (0.88)

Technology: Information Technology > Artificial Intelligence > Representation & Reasoning > Uncertainty (0.34)

Remote Operated Vehicle, ROV is the new concept equipment being made to replace the manned systems, both manned submersibles and deep-sea divers. The performance of ROV is strongly dependent upon its tether cable that is subjected to hydrostatic and hydrodynamic forces in addition to the gravity and inertia forces. As the operational depth of ROV increases, the behavior of tether cable becomes more and more complicated and the dynamic analysis of the cable become important as well as expensive and complicated for the safety of ROV operations. In this paper, a dynamic analysis scheme as well as the relevant computer program that is efficient and relatively simple, for the prediction of the behaviors of the cable and attached ROV system is developed. The scheme is valid for the analysis of a single, nonlinear, three-dimensional and static/dynamic model of a submersible cable and attached system. The lumped mass method with Houbolt integration algorithm and Newmark method are basically employed here. In this method, the continuous distribution of the mass of the cable is replaced by the discrete distributions of the lumped masses at the finite number of points on the cable, resulting in relatively simple and effective analysis. Consequently the external forces on the cable can be simplified and calculated only at the nodal points.

ROV is the new technology equipment being made to replace manned systems, both manned submersibles and divers. Principal task of ROV is to freely travel and steadily approach to an object in aqua-space and transmit video information of it to water surface by using tether cable, since electro-magnetic wave cannot be utilized in water, although it is very powerful means on land and in aero-space. Acoustic means is a possible substitute for wireless data transmission, but its capability is quite limited.

ISOPE-I-02-170

The Twelfth International Offshore and Polar Engineering Conference

SPE Disciplines:

On the basis of recent studies, contributions of swell to sea surface phenomena are discussed. It is shown that the attenuation of wind waves by swell depends not only on swell steepness but also on the ratio of the frequency of the swell to the spectral peak frequency of wind waves. It is also shown that the measured growth rate of swell in a wind area agrees well with the empirical formula of Hsiao and Shemdin (1983) in a region of small inverse wave age, while it approaches to the empirical formula of Mitsuyasu and Honda (1982) in a region of large inverse wave age. Finally, short discussion is given on the increase of surface drift current by opposing swell by using the result of recent study on Langmuir circulation (Mizuno, 2002).

ISOPE-I-02-268

The Twelfth International Offshore and Polar Engineering Conference

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