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to

GoAfter six years of negotiation the Antarctic Treaty Consultative Parties (ACTPs) reached agreement on a Convention for the Regulation of Antarctic Mineral Resource Activities (CRAMRA). The agreement is not a code of detailed regulations, but rather a set of standards and criteria upon which decisions about possible future Antarctic mineral resource activities must be based. Five institutions are established to administer the entire process. Activities must proceed in three distinct stages: prospecting, exploration and development. No activity can proceed beyond prospecting unless there is a unanimous decision by the Commission to open an area for exploration and possible development. Decisions for mineral resource activity cannot be made until there is adequate informat10n to make informed judgements on the possible environmental impacts. No activity can ta~e place unless the technology and procedures are available to: meet the strict standards of the treaty, to monitor the impact of the activity, and to respond effectively to accidents. The agreement contains many restraints and controls on mineral resource activities. Any operation that poses an environmental threat can be shut down. It 1S apparent from all the checks and balances in the convention that it is not an open invitation to develop the mineral resources of Antarctica. Although the future of the agreement is somewhat clouded, what is clear is that it will be many years before there is any significant mineral resource activity in Antarctica, if ever.

ISOPE-P-90-006

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

activity, agreement, antarctic mineral resource activity, Antarctica, Commission, Convention, decision, development, exploration, Exploration Development, health safety security environment and social responsibility, management, metals & mining, mineral, operator, regulatory committee, resource, Treaty

Country:

- Europe (1.00)
- North America > United States (0.35)

Industry:

- Materials > Metals & Mining (1.00)
- Law (1.00)
- Government (1.00)

SPE Disciplines: Health, Safety, Security, Environment and Social Responsibility > Environment (1.00)

A modified load transfer (t-z) analysis for axially loaded piles is presented in this paper. The method can be used to predict the full load-displacement behaviour of a pile, and unlike the conventional t-z analysis It IS also capable of indicating the complete mechanism of load transfer as well as the complete stress path at the pile-soil interface. It is able to do this by assuming as input a constitutive model for the pile-soil interface that permits coupling between the shear and normal modes of deformation. The use of the technique is illustrated for a driven and grouted pile in calcareous soil

INTRODUCTION

Many fixed offshore platforms used for the recovery of natural hydrocarbons are supported on pile foundations. In a number of regions of the world, e,g. off the coasts of India, Australia and in the Persian Gulf, the sub-sea soil conditions Consist of significant deposits of calcareous soils. This soil type has posed a number of difficult problems for designers of these offshore platforms. These low values of skin function are largely a result of the crushing of the Soil around the piles during driving, which gives rise to low normal stresses acting on the pile and hence low frictional shear resistance. Recently, some offshore platforms have been designed to be supported on piles which are either fully or partially grouted into the calcareous medium. In some cases, primary piles are driven to the appropriate depth, and then secondary piles are constructed by augering a cylindrical hole and grouting a steel pipe insert below the primary piles. In other cases the piles are driven and then cement grout IS injected through tubes that pass down the inside and through the walls of the pile. The latter are referred to as driven and grouted piles.

ISOPE-P-90-038

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

This paper analyzes the results of the theoritical studies of the spirally re1nforced compos1te mater1als oota1ned by using a new model of calculation of the behavior of the material unter two types of conditions: 1- auxiliary layer and inner part of the structural element are Isotropic.2-auxiliary and inner part of layer is orthotropic the element is transversally isotropic. The paper gives on est1mat1on of the influence of the layer properties on the compos1te''s state of strain as well as the calculation of carbon reinforced epoxy-bended plastic conducted for the case of planar state of stress by specially developed computer programme. The requirements to be satisfied by the composite materials have to correspond to the types of the pasts of constructions for Which they are produced. It 1S not rear that such requirements demand new types of composites for Which theoretical and experimental studies would have to be conducted in order to obtain materials with optimal caracteristiques. This paper considers the influence of auxiliary layer composite materials created on the basis of spirally wound reinforcing filling agents. Elementary structural unit of spirally reinforced material is obtained by disposition on the surface of the main reinforcing filling agent an intermediate layer formed of fibrous filaments. dimensions of winding, and characteristics of which differ from those of the main filling argent. Microstructural studies of the composite have assessed as in works [8.9] that the disposition of structural units in material is hexgonal and the main reinforcing filling agent (zone 2., ) is an infinite cylinder of a circular cross section the generating line of which is perpendicular to the plane xOy the lntermediate layer (zone 1) has a form of a void cylinder and a matrix (zone 2) represents an lsotropic body.

ISOPE-P-90-126

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

The dynamic characteristics involved in the loading process in the ocean environment are complicated and difficult for exact evaluation of the response of offshore structures From the engineering point of view, it is Important to obtain reasonably reliable results by means of simplified descriptions of the complex problems. This paper investigates the effects of those simplified descriptions on the dynamic response evaluations of offshore structures Parametric studies based on the perturbation method are presented to assess the influence of uncertainties associated with various assumptions and approximations. These uncertainties are represented by the inertha coefficient, the drag coefficient, the mean wave height and the shear wave velocity of the soil it is found that among -all the parameters considered in the present study, variations in the mean wave height provide the most significant contributions to the dynamic response it is suggested that in order to perform reliable design of offshore structures, it is important to clarify the uncertain parameter effects on the response evaluation.

The environmental loads such as waves, winds and earthquakes acting on any offshore structure are dynamic and highly random in nature. On the other hand, the uncertainties in the properties of the material and in the characteristics of the foundation soil may also give use to some statistical variation in the eigen values and eigenvectors of the structure (Boyce, 1968) and consequently the dynamic response may be affected (Kareem and Sun, 1986). The analysis and design of offshore structures is an extremely complicated process and requires several assumptions and approximations. Empirical models such as the Monson equation for the wave force or the expressions for the wave energy such as the Bretschneider''s spectrum involve several coefficients which have to be determined by experiments or field observations and have to be extrapolated to a particular problem.

ISOPE-P-90-041

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

coefficient, contnbutlon, drag coefficient, dynallllc, dynamic lesponse, dynamic response, dynarmc response, effect, formation evaluation, log analysis, mertla coeffiCIent, method, Offshore, Offshore Structure, penod, platform, research, Reservoir Characterization, reservoir description and dynamics, Response, seismic processing and interpretation, structure, Upstream Oil & Gas, Wave, well logging

The recent research achievements on stress analysis of tubular joints in China are presented in this paper. Both theoretical analysis and experimental research on the elastic, elasto-plastic and rigid-plastic behaviour of tubular joints are investigated.

There are two main kinds of limit states of tubular joints in offshore structures, such as fixed platforms and semisubmersible drilling vessels. One is the fatigue failure limit state related to the damaging effect of repeated loading and the other is the ultimate limit state, corresponding to the maximum carrying capacity. The occurence of high stress is the main cause of brittle fracture (high cycle fatigue). Sometimes, in the condition of bad huge storm, the plastic deformations occurred at the large part of the intersection curve of tubular joints is the main cause of low cycle fatigue failure (ductile fracture). The recent research actives on computing methods for elastic, elasto-plastic, rigid-plastic analysis of tubular joints and experimental works on steel models, photo-elastic models of tubular joints carried in China are presented in this paper.

The elastic analysis of tubular joints by analytic method was firstly carried out by Bijlaard(1) and Dundrova (2) thirty years ago. Owing to the difficulties in mathematical analysis only the stress distribution of chord tube could be found, and the analysis is limited to tubular T-joints, meanwhile the transfer loads between branch tube and chord tube are based on assumptions. Hence these analysis are somewhat empirical. The sem1-analytic method for the stress analysis of tubular Joints was investigated firstly by A.C. ScordeliS (3). He assumed that the vertical displacements of the chord tube around the intersection curve is uniform with magnitude same as the vertical displacement of top end of branch tube, i.e. the branch tube is considered as a rigid tube.

ISOPE-P-90-144

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

SPE Disciplines:

This paper- concerns a simple calculation using the known results of uniformly distributed load, of static bending problems of some cases of axisymmetrically loaded circular plates With mixed boundaries on the entire edge The use of a Fourier series Expansion to fit a mixed boundary condition results many coupled equations for finding the Fourier coefficients An effective method i e the coefficient comparison method presented In this paper depends on a known solution for uniformly loading.

Many circular plates are widely used as one of basic elements of various Industrial plate structures Including marine structures. Therefore, a number of researchers have dealt so far with the problems of bending, vibration and buckling of Circular plates having mixed boundary conditions Leissa and Clausen (967) studied -the case of a Uniformly loaded Circular plate having clamped and simply supported portions of Its boundary by using the point-matching method Conway and Farnham (1967) studied a uniformly loaded Circular plate which have Simply supported-clamped, simply supported-free or clamped- free combinations of edge condition. Stahl and Keer (1972) treated the case of a uniformly loaded Circular plate which have clamped-simply supported and Simply supported- free combinations In their study the -problem was reduced to a Fredholm Integral Equation of the second kind for an unknown auxiliary function. More recently, Hamada, Mizushima and Mifune (1987) treated by using an Iterative method the bending problem of a circular plate whose elastic restraint for the radial slope vanes along the edge Klattikomo and Sriswasdi (1988) treated a Uniformly loaded annular Circular plate which have simply supported-clamped combination of edge condition on the outer edge and free condition on the Inner edge. The bending problem of circular plates and annular circular plates under various types of loading art Important and have many applications In structural Engineering.

ISOPE-P-90-162

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

Influence of the local brittle zone on HAZ CTOD was discussed. From weld HAZ CTOD tests and simulated HAZ CTOD tests, it was clarified that the local brittle zone of a multi-pass weld HAZ is intercritically reheated coarse-grained zone, where high-carbon martensitic island was formed. Factors influencing the formation and decomposition of high-carbon martensitic island (M*) in the intercritically reheated coarsegrained HAZ was investigated. Based on a simple estimation model of volume fraction of the M*, it became possible to estimate quantitatively the influencing factors on the formation and decomposition of the M*. It was clarified that combination of steel with low carbon, low microa110y chemical composition and suitable welding condition, such as application of preheating and thin weld bead placement, is important for reducing or eliminating the H*.

Since low CTOD (Crack-Tip Opening Displacement) value was obtained in a HAZ (Heat-Affected Zone) CTOD test of offshore structural steel in the early 1980s, extensive studies have been made to clarify the cause of the low CTOD value. It has been made clear that the low value was caused by the LBZ (Local Brittle Zone) in the HAZ. Factors influencing the microscopic toughness of the LBZ and measures to prevent low CTOD value have been studied (OMAE, 1988),(OMAE, 1989) and new steels which have high HAZ CTOD value have been developed (e.g. Chijiiwa et aI, 1988). For improving the LBZ toughness, selection of chemical composition which has low susceptibility to cleavage fracture is primarily important. In addition, selection of a suitable welding condition (heat input, preheating and bead placement etc.) is also important. For this purpose, it is of urgent necessity to elucidate these factors quantitatively. From this standpoint, the present paper will discuss the factors controlling the LBZ toughness.

ISOPE-P-90-120

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

chemical composition, cleavage fracture, concentration, CTOD, decomposition, factor, fraction, fracture, HAZ, high-carbon martensitic island, Influence, ircg haz, Microstructure, offshore structural, reservoir description and dynamics, simulated haz, simulated haz ctod, steel, toughness, transformation

Fatigue behavior of 2024-T3 aluminum alloy is caracterized for the role of compressive portion of constant or variable amplitude loading conditions which include single or periodic single peak compression overloads. It is found that the compressive load cycles have a remarkable effect on crack propagation as well as crack initiation. Particularly, it is noticeable that, under high baseline load ratio without crack closure, the non-propagation crack arrested by single peak tension overload recommenced to propagate by following single peak compression overload. Such results are discussed in terms of crack opening level, reversed plastic zone size, residual deformation on the crack surfaces and so on.

Conversely, the effect on fatigue crack propagation is generally considered to be minimal, since the creek is expected to be fully closed during the compressive portion of the cycle, necessitating a stress intensity of zero at the crack tip (Hudson et aI, 1974). Similarly, it is found that compressive overload cycles In general have little effect under variable amplitude loading, except when they immediately follow a tensile overload where they act to reduce the post-overload retardation (Schijve et aI, 1962; Stephens et al,1976). In such tests, however, the crack growth rates were analyzed with respect to not the effective stress Intensity range (11 K. If) but the nominal stress intensity range (11 K) which rely on only the tensile portion of the load cycle, so that one of the most Important effects of compressive portion of the cycle, I.e., reduction of crack opening level were neglected. On the other hand, some studies show compression stresses have a strong effect on the crack opening level and increase crack growth rate in both stages of near- threshold and steady- state crack propagation (Newman, 1984; Yu et al. 1984; Kurihara, 1986).

ISOPE-P-90-114

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

A brief overview is given of researches on the prediction methods of hydrodynamic force on a body moving in waves and having a steady -advance speed. Then two methods developed by the present author for computing hydrodynamic forces are presented and their results are discussed. These two methods are based on different assumptions of the steady flow field around the body.

Prediction of hydrodynamic forces on off-shore structures in current as well as in waves or towed in waves must be based on the correct understanding of current-wave interaction effect . There are other less obvious contexts in which this effect must be considered. Slow drift oscillation in waves is of so large amplitude and long period compared with wave motions that it may be considered as a quasi-steady movement. Damping of the motion may be predicted as a steady force when assuming they move at a steady speed in waves backward or forward. Tilt moment on the structures in waves is caused by vertical steady force. This will be affected when they make slow drift oscillations. That means the tilt moment is also to be predicted taking into consideration that the structures are moving in waves at steady speed. In this chapter I give a brief, I never intend it complete, review of recent researches on prediction of hydrodynamic forces on bodies moving at constant speed in waves. Description is restricted to the potential theories. Correct prediction of hydrodynamic forces on a floating body moving at steady velocity in waves has been mainly a concern of ship hydrodynamics. In the contexts-of seakeeping of ship, however, ship''s geometrical form is often assumed very slender. Prediction of those forces on bluff bodies such as off-shore structures is quite a different problem.

ISOPE-P-90-075

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

ISOPE-P-90-054

The First ISOPE Pacific/Asia Offshore Mechanics Symposium

SPE Disciplines: Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Offshore pipelines (1.00)

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