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**Industry**

**Oilfield Places**

**Technology**

This paper presents a result of an analysis of the nonlinear Interaction and response of the coupled ISSC-TLP System to the random seas In the time domain The environmental load also includes the effect of the concurrent steady winds and currents. The first- and second-order wave-exciting forces are calculated using a robust higher-order boundary element method (HOBEM), while the nonlinear tendon dynamic analysis is performed using the three-dimensional hybrid element method with the updated Lagrangian formulation. The Monson equation is employed for the wave and current load on slender structures The analysis is focused on the nonlinear responses due to the nonlinear environmental load and nonlinear interaction between the platform and tendons that Includes the offset, setdown, large coupled surge-heave motion In the low frequency and Resonant heave/pitch responses with the springing loads In the high Frequency.

This paper presents an analysis of the nonlinear interactions and responses of the coupled ISSC-TLP In the long-crested random seas m concurrence with the steady action of the wind and current The TLP system is a compliant platform whose mooring system has soft lateral and stiff vertical restoring forces, which create the lateral and vertical mode resonance motions m the low and high frequencies, respectively. The responses of the TLP system near the resonance frequencies are activated by the second-order nonlinear wave exciting forces. The nonlinear lateral environmental load induces a large drifting oscillation and brings the platform to Its mean drifted position (offset) and the setdown of the platform. The TLP system then oscillates around the mean shifted position. Under the circumstances, the tendons may non-linearly respond due to its large geometrical displacement the heave/pitch resonant motions induce the springing tension loads m the tendons which are Important for the fatigue estimate.

ISOPE-I-94-008

The Fourth International Offshore and Polar Engineering Conference

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (0.34)

For an accurate analysis of the forces during ice-structure interaction it is necessary to use a correct material model for the Ice. An elasto-viscoplastic constitutive material model is able describe elastic, plastic and viscous deformations, which all are present during ice-structure interaction. The creep behavior of the material model is usually assumed to be purely viscous (i.e. secondary creep) and governed by Glen''s law. Neglecting primary creep will lead to an underestimation of creep strains in the initial stages of the deformation process. How this affects the indentation force is not known. In the present study, both primary and secondary creep deformations are considered. Different mathematical models for creep deformations in ice are investigated. These models are adopted in analysis of ice indentation problems using the finite element method. The numerical results show that the effect on the maximum indentation force of including primary creep in the material description is negligible, whereas the effect on the creep process itself is large.

Since ice is present in nature at a very high homologous temperature the mechanical behavior is rate and temperature dependent. Time-dependent deformations, usually referred to as creep, play an important role in a wide variety of ice mechanics problems. At low stresses and high homologous temperature creep strains usually dominate over other components of strain. Numerous publications have dealt With the experimental determination of creep deformations in ice under various loading and environmental conditions. One of the first constitutive models describing creep in ice was Glen''s law, Glen (1955), and is still widely used. Glen''s law neglects primary creep or delayed elasticity and only considers the viscous part of the creep process. Ashby and Duval (1985) reviewed several creep equations given in the literature and separated between phenomenological equations, where macroscopic variables are related, and constitutive equations which are more based on physical models.

ISOPE-I-94-152

The Fourth International Offshore and Polar Engineering Conference

Oilfield Places: Europe > Denmark > North Sea > Danish Sector > 7/89 License > Block DK 5604/29 > South Arne Oil and Gas Field (0.97)

The development and use of an expert system to recommend coatings for flue gas desulfurization (FGD) plant is described. The system ranks coatings by their material properties, experimental test and plant performance scores when the component to be coated and its working environment are specified. The user interface, the inference engine, the knowledge base and the implementation of the expert system are presented with comments on its suitability and application for corrosion consultations.

Flue Gas Desulfurization (FGD) (NACE 1981) has become a very common term within the utility industry and among those associated with air pollution control. As our power generation facilities continue to expand the use of coal as a primary fuel, the need for effective and reliable FGD systems becomes important if we are to have environmentally acceptable plants. It is shown in this paper that the purpose of this study is to examine typical FGD systems purely from the standpoint of corrosion. Therefore, a corrosion consultant expert system (CCES) is developed. CCES is a knowledge-based expert system, and is developed with GURU (MDBS 1991), an expert system development shell. CCES consists of a rule set and two databases (Date 1986). The rule set includes the basic rules to be used in the inference process. The first database maintains application and material property for various coatings and linings. The second database maintains historical performance data. When an FGD component and its service environment are specified, CCES can be used to obtain a list of recommended coatings tabulated in order of their ranking scores. In the system a user interface module, written in GURU''s procedural language, is used to direct the overall consultation process and to provide the link between the system and the user. The inference process is driven by GURU''s inference engine according to the expert''s knowledge stored in the rule set.

ISOPE-I-94-301

The Fourth International Offshore and Polar Engineering Conference

SPE Disciplines: Management and Information > Information Management and Systems > Artificial intelligence (1.00)

Vortex induced motion of risers in a steady, uniform flow has been investigated experimentally in subcritical flow in a water flume and under critical flow conditions in a high speed cavitations tunnel. Both experimental arrangements provided flexibility in the in-line direction as well as transverse to the flow. Considerable in-line motions were seen in combination with the dominant transverse motions, and the latter were different from those observed in the case where transverse flexibility only was allowed. The tests at critical Reynolds number showed some 80% increase in the average drag coefficient, compared to the results for a fixed cylinder. This is oil much more modest increase than for the subcritical flows where an increase of 2-300% was found. The transverse motion amplitude reached a maximum of almost one diameter, which was slightly smaller than for the subcritical case.

Flow-induced motion of flexibly supported circular cylinders in steady currents is a classical problem, and one that is o~ great practical significance in many fields. It has been the subject of numerous papers. Though progress has been made and several aspects of the problem are reasonably well understood, there are still very important unresolved questions. For general reference Blevins (1990) or Griffin (1985) may be consulted. The present paper is based on an experimental investigation which was performed as a joint industry project in 1984. A draft of this paper was written in 1985, but it had to be withdrawn from publication at that time. The engineering problem that motivated this investigation was the dynamics of riser lines from the seafloor to floating oil or gas producing platforms in considerable waterdepths, say 300-1000 m. The approach used was model tests of short, spring supported pipe sections in steady flows. The idea was to treat the full length risers as a series of such flexibly supported sections.

ISOPE-I-94-248

The Fourth International Offshore and Polar Engineering Conference

SPE Disciplines:

The present paper deals with the development of a testing device for quick offshore geotechnical investigations. The equipment, at present, consists of a penetrometer, mounted on a sea bed platform, a handling frame and a control cabin; a further development will include a drill rig and a geotechnical laboratory. All this is designed so as to be an autonomous unit that can be handled by various types of non-specialized ships which have the necessary deck space. The sea bed platform can operate in 2000 m of waterdepth and is provided with an hydraulic penetrometer, with a thrust capacity of 400 kN, able to carry out cone penetration type testing until a depth of more than 100 m, as well as shallow ,depth continuous sampling_ The penetrometer can be equipped with a series of probes (piezocone, pressiocone, total radial pressure transducer, seismic cone) allowing the execution of the wide range of direct geotechnical measurements normally performed during on-land penetration tests.

The present paper deals with the development of a new and powerful testing device, named "ABYSSIE" (ABYSsal Soil Investigation Equipment), for exhaustive and quick offshore geotechnical investigations. With this new equipment, designed to operate at very deep sites, Ismes S.p.A. (Bergamo, Italy) has imp Loved its capabilities in Offshore Activities, being the offshore field the natural extension of its decennial experience in the execution of in-situ testing and the development of new geotechnical testing equipment. An equipment for testing very deep soils finds its reason for existence in the general consideration that offshore activities are moving rapidly out off the continental shelf, onto the continental slope and into great water depths, say more than 1000 m, where new developments entails more than a mere extension and adapt ion of familiar principles and procedures (Hoeg K., 1986).

ISOPE-I-94-060

The Fourth International Offshore and Polar Engineering Conference

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (0.61)

Kamoi, Norriyuki (Kawasaki Heavy Industries, Ltd.) | Taniguchi, Tomokazu (Kawasaki Heavy Industries, Ltd.) | Kiso, Takashi (Kawasaki Heavy Industries, Ltd.) | Kada, Kazuo (Kawasaki Heavy Industries, Ltd.) | Motoi, Tatsuya (Kawasaki Heavy Industries, Ltd.) | Nakamura, Shinichi (Kawasaki Heavy Industries, Ltd.)

There are few actual ship measurement data showing the propriety of the design loads given by classification societies rules or other relevant rules Therefore, we measured acceleration of ship motion and fluctuating loads on tank supports and chocks of a 75,000 m

1.INTRODUCTION

Kawasaki Heavy Industries, Ltd has delivered a total of eight 75,000 m3. Independent prismatic tank type LPG carriers since July 1990. In designing them, the authors carried out extensive structural strength analyses by most advanced FEM and very close fatigue strength analyses, and verified the propriety of such designing and analysis methods through stress measurement, etc. done In the tank test. In these ships'' designs, the authors used the dynamic loads provided for in classification societies'' rules, etc, but actual ship measurement data showing the propriety of these dynamic loads are few. Therefore, for the purpose of making clear the dynamic loads acting on the hull structure and their frequency and verifying the propriety of the design loads used in designing these ships, the authors measured ship motion accelerations, stresses of the tank support structure, etc on board "Tsugaru Gloria" over about 1~3 years.

2.OUTLINE OF THE SHIP

(1) Principal Particulars and General Arrangement The ship''s principal particulars and general arrangement are shown In Fig 1 (2) Tank Structure and Tank Support Structure The cargo tank structure and the tank support structure are shown In Fig 2.

(Fig 1,2 are shown in the paper)

ISOPE-I-94-345

The Fourth International Offshore and Polar Engineering Conference

ABSRTRACT

The treated soil plant barge, Hakuren-go, and treated soil placing barge, Hakusei-go, have entered into service to construct a slope embankment (length 800m, breadth 83m, water depth 31 to 3m) on the sea bottom around the Kisarazu artificial island of Trans-Tokyo Bay Highway. The embankment will be formed with 993000m treated soil. The soil mixture prepared on the plant barge is pumped out by ten concreat pump units onto the placing barge. 6000m/day of the soil mixture is placed on the sea bottom using two sets of ten guide and tremie pipings alternately under the monitoring and controlling in the integrated operation room on the placing barge.

PREFACE

Trans-Tokyo Bay Highway shall have a connection between Kawasaki city, Kanagawa Prefecture and Kisarazu City, Chiba Prefecture passing through the center of Tokyo Bay, by under sea bottom tunnel (length 9.5km) and bridge (length 4.4km). The bridge connects to the under sea bottom tunnel through sloped embankment of artificial island. (Fig. 1) The treated oil paInt barge Hakuren-go and the treated soil placing barge Hakusei-go are newly planed and fabricated to be used for construction of the sloped embankment in February 1992.

OUTLINE OF THE TREATED SOIL EMBANKMENT

The sloped embankment shall be mounted on the sea floor With the treated soil which consists of pit sand, mud-stone slurry. cement and seawater. (Fig. 2) After construction. the embankment shall be bored by sealed boring machine for tunnel. Mixture proportion and strength of the treated soil shall be decided by the following performance; To hold the shape of the embankment. Easy execution of tunnel boring works. Therefore. the treated soil is required to keep constant mixing proportion during mixing and placing. The construction period was allowed two years only for placing. Both barges were planed and built newly for completion of the embankment under the above service condition.

ISOPE-I-94-033

The Fourth International Offshore and Polar Engineering Conference

arrangement, barge, cement, component, construction, control, embankment, Fig, pit sand, plant, pump, slurry, SOIL, soil mixture, Soil Plant, stage, tremie pipe

A direct version of the Boundary Element Method (BEM) based on the fundamental solution of the Laplace operator is formulated and implemented to analyse hydrodynamic interaction phenomena of closely situated bidimensional floating bodies in linear beam seas of finite depth. Added mass, radiation damping coefficients and amplitude response as a function of the exciting wave length for one and two half circular cylinders are reported Compared to a Greeen''s function implementation (Chen and Mahrenholtz,1992) this approach avoids the so called irregular frequencies and presents the possibility to incorporate variable seabed depth in the neighborhood of the bodies.

Hydrodynamic interaction phenomena play an important role in offshore angering. Examples include the interaction of vessels in the vicinity of floating or fixed harbours, the dynamic interaction between two closely situated floating bodies, connected or not. Catamaran ships and complex offshore platforms consisting of many interacting bodies may also be cited. The hydrodynamic forces acting on these structures and their amplitude response are influenced by the presence of other surrounding bodies or structures. So the dynamic analysis of floating or submerged bodies must include the diffraction-radiation effects of all nearly situated structures. A realistic analysis may only be accomplished by numerical techniques. There are two main numerical schemes to treat hydrodynamic interaction among floating bodies. The first category is represented by the Finite Element Method (FEM). The other scheme is the Boundary Element Method (BEM). Both methods present relative advantages and drawbacks. The FEM requires boundary dampers to account for the radiation condition (Leonard, 1983). The BEM offers the advantage that only the boundary of the domain under consideration must be discretized. This implies in enormous savings in data preparation efforts and processing capabilities, specially for three dimensional analysis furthermore the radiation condition is naturally satisfy in the be formulation.

ISOPE-I-94-215

The Fourth International Offshore and Polar Engineering Conference

The problem of high-frequency transient responses of Tension Leg Platforms, TLPs, under certain severe sea situations has been known for some time. Until recently, it was not known that this type of loading and response mechanism could produce tether loads of critical importance to the structural integrity of such structures. Presently, there is considerable ongoing discussion as to what causes tether ringing. NPD (1992) assembled a document where the views of the Norwegian Shelf operators and one Norwegian engineering company were summarized. At present there seems to be consensus that ringing, at least to a large extent, is caused by nonlinearities in the free surface variable wetting region of the TLP. Ringing is not predicted by linearized frequency domain analysis methods. There are a number of variable wetting contributions. Some of these are fairly obvious whilst other are less straight forward. A number of the contributions, of purely theoretical or engineering nature, identified to date are discussed in this paper. Based on this an intuitive method for ringing analysis is presented. It should be noted that the views expressed in this paper is the vies of the author and not necessarily the views of Norvegian Contractors.

There has been a number of proposals for formulating analysis models. These proposals range from simple Morison type models to a complete nonlinear formulation of the free surface interacting with the TLP columns. Jefferys (1993) shows that the use of Rainey''s

ISOPE-I-94-005

The Fourth International Offshore and Polar Engineering Conference

amplitude, analysis, coefficient, column, correction, effect, force, frequency, model, model test, not, order, Response, ringing, surface, tether, time, Wave, wave surface

Wave forces acting on the triangular roughness elements are experimentally investigated in 2-dlmenslonal wave flume. The roughness elements are modeis of ridges of the unconsolidated washboard-like rocky sea bottom surface comprized of an alternatlon of geosynclinais strata. Horizontal wave forces acting on the elements are manly composed of drag and inertia forces. The drag force is the prominent force component. Vortices separated from the roughness elements cause the drag forces. They are influenced by the shape of roughness elements and the distribution distance between adjacent roughness elements. Vertical forces are consisted of the drag, inertia and lift forces and hydrostatic pressure variation-caused forces, which are complicatedly mixed.

With increasing demand of mull-purposes utilization of nearshore sea area in recent years, the construction slate of offshore structures for control of sea environment are expanding to many places, the bottom surface conditions of which are sandy bottom, sandy and silty bottom, rocky bottom, etc. In the intermediate water depth. A washboard-like rocky sea bottom surface is found where an al iteration of geosynclinals strata, like a flysch, exists prominently under the sea. Ridges of the bottom suffer not only a skin friction but a drag force and an inertia force by wave action of strong wind waves. A prediction of the rocky sea bottom change and discussions on stability of the rocky sea bed need information’s on the wave forces acting on the ridges of the bottom surface. In particular, the wave force is very important and key factor when the rocky bottom is comprised of unconsolidated materials. The forces acting on pipelines (Shankar et al.,1988, Tsuchiya and Yamaguchi, 1974) and spheres (Iwata and Mizutani, 1989) near and on the sea bottom are investigated in detail, however, the geometrical scale of the ridges are smaller than those of the pipelines and spheres.

ISOPE-I-94-209

The Fourth International Offshore and Polar Engineering Conference