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GoThe stress corrosion cracking (SCC) resistance of two types of AI-Zn-Mg-Cu system alloys, including of the superplasticity material of fine grain structure prepared by thermo-mechanical treatment and the commercial material of coarse gram prepared by conventional process, was evaluated. The SCC resistance of two types materials was greatly different AI-Zn-Mg-Cu system alloy with come grain was superior to the alloy with fine grain. In tins study, the effect of X-ray residual stress and micro strain to the SCC resistance in two alloys were discussed on the basis of experimental results. The main results obtained in the present work are as follows (I) The values in macro residual stress of AI-Zn-Mg-Cu system alloys with fine grain and coarse gram measured by X-ray analysis were compression. The compression stress in coarse grain was higher than that in fine grain. The SCC life of the test materials existing on macro residual stress was longer with increasing compression one. (2) The micro strain were estimated by X-ray method. The values in micro strain of the alloys with fine grain was larger than that of the coarse gram. The SCC life of the alloy was longer with decreasing micro strain (3) The SCC resistance of the materials can be estimated by the residual stress and micro strain by X-ray analysis

AI-Zn-Mg-Cu system alloys are well known as an aluminum alloy with both of excellent workability and tensile properties. However, in tin series of the alloys, the resistance of stress corrosion cracking, SCC, became to be lower with increasing the strength. It was very Important to know that relation between the SCC resistance and the characteristic of the alloys. The AI-Zn-Mg-Cu system alloys evaluated in tins study were made by the thermo-mechanical treatment Therefore, the alloys will be exist on the macro residual stress and micro strain.

ISOPE-I-96-332

The Sixth International Offshore and Polar Engineering Conference

This paper is to investigate experimentally and theoretically the topographical change around the submerged moored structure under wave action in shallow water depth. Elaborate laboratory experiments on movable sandy bed have been carried out and revealed that the topographical changes under the structure are mainly classified into two patterns such as a partial scouring and an overall scouring. In addition, the wave-induced circulation current is revealed to occur around the structure, which is characterized by the on-shoreward current above the structure and the off-shoreward current below the structure. Next, a numerical calculation method is proposed to predict the bottom topographical change. The change of bottom topography evaluated numerically with the proposed method is shown to be in good agreement with experimental measurements.

Submerged offshore breakwaters have been constructed in order to protect the sandy beach from severe erosion as well as to prevent the wave-caused disasters in coastal zone. Most of the submerged structures constructed in the field is the bottom-seated structure made with concrete armor blocks or natural stones. This kind of the submerged bottom-seated structure has been frequently reported to suffer from severe movement of armor blocks or stones resulting in washing out the filling rubble stones by severe storm waves. The submerged moored structure is one type of the submerged structures and has been verified to be an effective countermeasure work against beach erosion, and cuspate spits are formed onshore side of the structure (Iwata et al.(1990)). The local scouring under the submerged moored structure, however, has been also pointed out to take place (Iwata et al.(1990)) The characteristics of the local scouring have not been discussed in depth yet, and therefore, there are many rooms to investigate the bottom configuration change around the structure. With the above-mentioned in mind, the bottom topographical change around the submerged moored-floating structure is studied experimentally and numerically in relation to wave characteristics and structural shapes and mooring conditions.

ISOPE-I-96-235

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)

Lei, Hin-Chi (Dept. of Civil Engineering, National Central University) | Chang, Huei-Wen (Dept. of Civil Engineering, National Central University) | Hung, Ming-Jui (Dept. of Civil Engineering, National Central University)

It was believed that the Lagrangian coordinate system is the most appropriate one to be used in finite strain theory of soil consolidation. The disadvantages of using the Eulerian and convective coordinate systems were described in the papers by Gibson et al. (1967 and 1981). In fact, the convective coordinate of a material point is a function of time and the Lagrangian coordinate, and thus it is an unknown in a consolidation problem. This, as is well-known, will cause mathematical inconvenience. However, in this paper it is shown that, when formulated in a coordinate system which differs from the convective coordinate system only by a function of time, the equation proposed by Gibson et al. (1967 and 1981) becomes linear if the effect of the self-weight of solids and pore fluid are neglected and the function which plays the role of a coefficient of consolidation is chosen properly. Using this fact we can obtain exact solutions to the equation developed by Gibson et al .. In view of the nonlinear character of the finite strain theory of soil consolidation, any exact solutions are important and noteworthy because they frequently reveal interesting phenomena and serve as a benchmark for numerical schemes.

In this paper we study the nonlinear theory of soil consolidation developed by R. E. Gibson and his co-workers (cf. Gibson et al. (1967 and 1981)). We concentrate on the equation of consolidation obtained by neglecting the influence of the self-weight of solids and pore fluid. We also make a special choice of the "finite strain coefficient of consolidation". A similar formula was also adopted in Feldkamp (1989). After we have expressed the nonlinear equation of consolidation in terms of the convective coordinate system we find a natural way of approximation to linearize the equation.

ISOPE-I-96-059

The Sixth International Offshore and Polar Engineering Conference

clay, coefficient, consolidation, convective coordinate, convective coordinate system, Denote, equation, function, Gibson, Lagrangian coordinate, management and information, material point, nonlinear, paper, Pore Fluid, reservoir description and dynamics, Soil Consolidation, solution, system, theory

SPE Disciplines:

Kozakiewicz, A. (BMT IBW Polska Sp. Zo.o.) | Sumer, B.M. (Institute of Hydrodynamics and Hydraulic Engineering, Technical University of Denmark) | Fredsoe, J. (Institute of Hydrodynamics and Hydraulic Engineering, Technical University of Denmark) | Hansen, E.A. (Danish Hydraulic Institute)

The study concerns the vortex-flow regimes around a cylinder exposed to an oscillatory flow and undergoing vibrations in the cross-flow direction. The flow of vortices was visualized, using the aluminum-powder technique. The study focuses on the lock-in regions. The tests have been carried out for the values of the Keulegan-Carpenter number KC=10 and 20, and for a range of reduced velocities. The identified vortex-flow regimes were compared with the fixed cylinder case. The changes to the vortex-flow patterns were discussed with regard to their influence on the lift force. To complement the results of the experimental study, an attempt has been made to simulate the flow numerically, using the discrete vortex model. The numerical results agree with the experiments.

The vortex-induced vibrations of slender structures can occur in both steady currents and wave flows. In steady currents, in the lock-in region, the vibrating structure takes control of vortex shedding, which leads to the amplification of the lift force; this, in turn, generates higher amplitude vibrations (see, ego Blevins 1976). When the amplitude of cross-flow vibrations reaches a certain value, the mode of vortex shedding changes. This apparently leads to a decrease of vibration amplitudes and jump in the phase between the vibrations and the lift force (Williamson and Roshko 1988). In wave flow, the cross-flow amplitude response of a freely-vibrating cylinder reveals the multi-peak behaviour; the lock-in occurs not only once but rather several times. Each of these peaks occurs at a certain value of the reduced velocity, V

ISOPE-I-96-227

The Sixth International Offshore and Polar Engineering Conference

amplitude, amplitude response, case, cylinder, fixed-cylinder case, frequency, inline, LIFT, management and information, numerical simulation, oscillatory, production control, production monitoring, reservoir description and dynamics, Reservoir Surveillance, Response, shed, Sumer, transverse, Upstream Oil & Gas, vibration, vortex, vortex-flow pattern, vortex-flow regime, vortice

SPE Disciplines:

This paper presents recent results of parametric studies on uniplanar and multiplanar K-joints with gap made of rectangular hollow sections. This analysis is based on Finite Element calculations verified by experiments. The investigations cover thin-walled rectangular hollow sections of commonly used dimensions and manufacture as used e.g. in crane constructions, conveyor belts, masts, etc. The finite element model employed has been optimized and checked carefully in two research programmes sponsored by the Deutsche Forschungsgemeinschaft DFG (German Research Foundation) dealing with uniplanar and multiplanar K-joints with gap. Compared to previous investigations, the influence of axial load, in-plane bending moments (IPB) and out-of-plane bending moments (OPB) are considered independently. Based on these results, parametric formulae for the calculation of the maximum strain concentration factors can be developed which are accurate enough from the Engineering point of view. Subsequently, characteristic SNCF diagrams for different load cases and in dependence of the main geometrical parameters are given.

Hollow sections can be very advantageous in certain fields of application and have been used in mechanical engineering as well as in structural engineering for a long time. Problems mainly occur at of joints and connections, particularly in the case of welded hollow section structures subjected to fatigue stresses. Hollow section joints exhibit local variations of stiffness, which lead to geometrical stress concentrations. The determination of the stress concentration factors (SCF) is essential for predicting the fatigue life of a structure on the basis of the hot spot stress range (S

ISOPE-I-96-253

The Sixth International Offshore and Polar Engineering Conference

In this paper, an undersea pipeline with different gap ratios(e/D=0.0, 0.2) in a regular wave field is solved numerically based on Large Eddy Simulation method (LES), using a hybrid method between a finite-difference method(FDM) and a finite-element method(FEM).A structured block grid system suitable for pipeline with different gap ratios(e/D=0.0, 0.2) is built up. The boundary condition is approximately the particle velocity calculated based on the stream function theory at the depth of the pipe center. The numerical results coincide with those of the physical model test quite well.

Pipelines are often used for offshore oil, gas development and other offshore applications. The wave forces acting on pipelines are the most important exciting forces, which depend on the flow behaviors around the pipes. Since the flow behaviors around pipeline are not so well understood and the designers can not determined the wave forces acturately, it is usually required to run model tests.B.M.Sumer etc.(1991) and A.Jamo-Druaux etc.(l995) have made much significant experimental progress in this field. With the development of hydrodynamics, it becomes possible to solve directly this problem numerically(Lee,Y.G. and Miyata,H. 1990). Numerically, the methods we have commonly used are finite-element method, finite-difference method, and finite-analytic method. As well known, the forces acting on pipeline by regular waves are mainly caused by viscous effect, namely, surface friction, flow seperation, wake and vortex effect. In such case, Reynolds number is quite high which usually cause the computation unstable and expensively. In the meantime, to build up a versatile grid system suitable for different gap ratios is also another challenging problem to solve. To overcome the problems, in this paper, firstly we build up a structured block grid system(Ge Wang,1994a) by the Thompson body co-ordinate transformation method suitable for pipeline with e/D=0.0 and 0.2. Secondly, we use large eddy simulation method to solve directly the N-S equations(Ge Wang,1995).

ISOPE-I-96-103

The Sixth International Offshore and Polar Engineering Conference

acceleration, Artificial Intelligence, circular cylinder, coefficient, Comparison, different gap, directional, experiment, model test, numerical simulation, oscillatory, pipeline, profile, Reservoir Characterization, reservoir description and dynamics, resultant force coefficient, solid line, subsea system, technology, University, Upstream Oil & Gas, Wave

SPE Disciplines:

New Seoul International Airport is being constructed on the West Sea between Yongjong Island and Yongyu Island, 52 km west of Seoul, in Kyunggi Bay. The construction work has begun since November, 1992 and the airport will be partially opened in the year of 2000 with completion of 1st stage of work. This project will be completed by the year of 2020. The total area of site development is about 56.168 km

New Seoul International Airport (NSIA) was first discussed around July 1988 because the rapidly growing air-traffic, noise level and other environmental effects. The Ministry of Transportation made a decision to construct a new airport on January 1989. The feasibility study of 22 sites located within a 100 Km radius of Seoul was carried out in the period of June 1989 through April 1990. Seven sites were selected and narrowed down to three sites, Yongjong Island, Shiwa I & II. A comparative analysis of the given three sites was carried out with considering various factors including airspace, obstacles, weather conditions, noise level, land usage, accessibility, and future expandability. The airport design criteria and standards recommended by the International Civil Aviation Organization (lCAO) were followed. After reviewing, analysis, and consultation with all concern parties, Yongjong Island was selected on June 14, 1990, as the [mal site for the New Seoul International Airport (NSIA).

ISOPE-I-96-060

The Sixth International Offshore and Polar Engineering Conference

Industry:

- Transportation > Infrastructure & Services > Airport (1.00)
- Transportation > Air (1.00)

SPE Disciplines: Health, Safety, Security, Environment and Social Responsibility > Environment (0.49)

The strength parameters of ice features on sea water areas have the high changeability in space and tune. It is a reason of it indefinition which can lead to big errors in ice force analysis. Therefore not only the parameters of ice structure interaction but the parameters of inhomogeneity of ice features must be considered in evaluation of design ice strengths. The necessity to account separately the three-dimensional inhomogeneity of ice cover. The program of experimental study of three- dimensional ice cover inhomogeneity is proposed accounting for the features of existing analysis method for ice force analysis. The test results will give the base for simple procedure to account the three- dimensional inhomogeneity of ice cover in design ice strength calculation.

The ice forces on offshore structures in many cases are basic and influence on the main parameters of structure. The oil and gas drilling platforms have the great capital and material cost and big crew. The damage of structure can lead not only to victims but to ecological catastrophe on site. Therefore the problem of correct analysis of ice forces is very important in connection with exploration of oil and gas fields in freezing seas. The ice forces on offshore structures depend on many factors: geometrical dimensions of ice features, combinations of different ice features action, drifting velocity, ice mass, added water mass, strength parameters of ice features, it structure, dimensions of offshore structure and so on. The ice strength parameters have the uncertain values depending on spatial and time changeability. So the right evaluation of ice strength have the great importance for more accurate ice force analysis. The most effective from this point of view is division of interaction process into two processes in different time scale: big and small (Bekker, 1990). It is more convenient for sea water areas with high dynamic ice regime.

ISOPE-I-96-133

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines:

The hydrodynamic properties of a dual pontoon floating breakwater consisting of a pair of floating cylinders of rectangular section, connected by a rigid deck is investigated theoretically. The structure is partially restrained by linear symmetric moorings fore and aft. The fluid motion is idealized as linearized, two-dimensional potential flow and the equation of motion of the breakwater is taken to be that of a two-dimensional rigid body undergoing surge, heave and pitch motions. The solution for the fluid motion is obtained by the boundary integral equation method using an appropriate Green function. Numerical results are presented which illustrate the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. It is found that the wave reflection properties of the structure depend strongly on the width, draft and spacing of the pontoons and the mooring line stiffness, while the excess buoyancy of the system is of lesser importance.

Floating breakwaters offer an alternative to conventional fixed breakwaters and may be preferred in relatively low wave energy environments or where water depth or foundation considerations preclude the use of a bottom-founded structure. Furthermore, in certain applications, aesthetic or water circulation considerations may require that the breakwater does not pierce the free-surface and/or extend down to the sea-bed. In the present paper, the behavior of a dual pontoon floating breakwater is studied. Various aspects of the two-dimensional problem of wave interaction with long submerged, bottom-founded or floating, surface-piercing structures of rectangular cross-section have been studied previously by several investigators. Both the diffraction (waves incident on fixed structure) and radiation (structure oscillating in otherwise calm fluid) problems have been treated. A variational formulation approach for rectangular bodies either on the free surface or on the sea bed was presented by Mei and Black (1969) and Black et al. (1971).

ISOPE-I-96-236

The Sixth International Offshore and Polar Engineering Conference

Operators are taking an increasing interest in deep water fields in the Gulf of Mexico. The reasons include discovery of better prospects and the advent of better, i.e. lower cost, technology for recovering the oil. One of the new technologies contributing to this interest is the deep draft Spar Production System. The first such system is scheduled for installation in September, 1996 at Vioska Knoll 826 for Oryx Energy Company and CNG (The "Neptune" Project). The water depth at VK826 is 1930 feet. This paper will provide a description of the production Spar, its major systems and performance. Particular attention will be placed on the design methodology. Improvements in spar technology being pursued in 2nd generation designs will be described.

A Spar consists of a vertical cylinder which provides buoyancy to support facilities above the water surface. Its stability is derived from the location of its center of gravity below its center of buoyancy. Station keeping is provided by lateral, catenary anchor lines which may be attached to the hull near its center of pitch for low dynamic loadings. Spar Buoy type structures have been used in the ocean before. For example, the Floating Instrument Platform (FLIP) was built in 1961 to perform oceanographic research (Fisher and Spiess, 1963). The Brent Spar was built by Royal Dutch Shell as a storage and offloading platform in the North Sea (Sax and de Werk, 1974). The Brent Spar was used for storage and offloading of oil. The present generation of Spars have the following features: -Full drilling and process facilities are housed on a deck supported by the spar. -Christmas trees for the wells are at the surface. -Rigid steel risers are supported in the centerwell by separate buoyancy cans. -Catenary mooring lines may be used for stationkeeping to assist in drilling, completion and workover operations.

ISOPE-I-96-039

The Sixth International Offshore and Polar Engineering Conference

SPE Disciplines:

Technology:

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