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**Industry**

**Oilfield Places**

**Technology**

**File Type**

The nonlinear viscous flow problem associated with the high frequency heave motion of a vertical column of a Tension Leg Platform (TLP) has been investigated numerically in a previous paper by the authors. It was found that the hydrodynamic damping force of a TLP column is very small. Adding appendages to the TLP columns is one of the choices to increase the heave damping force. The effect of an appendage in the form of a disk attached to the bottom of the vertical cylinder has been investigated in the present paper. Numerical simulation shows that the form drag component of the heave damping is changed dramatically compared to the skin friction component in the presence of the disk. The heave damping induced by the disk is linear with the amplitude of oscillation in the range of

The resonant oscillations of a Tension Leg Platform (TLP) in heave, pitch and roll excited by sum-frequency wave forces are referred to as "springing" (Faltinsen 1990) and can contribute to fatigue in tethers. The oscillations are typically of small amplitude and high frequency. Previous investigations (Huse1990, Huse & Utnes 1994, Chakrabarti & Hanna 1991,Thiagarajan & Troesch 1994, Thiagarajan & Troesch 1998, Tao et al 1998) have shown that for a lightly damped offshore structure like the TLP, increasing the damping level of the system in order to control the resonant springing oscillations becomes critical for design. The two main governing parameters for small amplitude oscillatory flow induced by the vibration of a vertical cylinder are Keulegan- Carpenter number and the frequency parameter.

ISOPE-I-99-297

The Ninth International Offshore and Polar Engineering Conference

SPE Disciplines:

Bolted flane-plate connections have always been a suitable solution for tension member joints. The main disadvantage is the unpredictability of prying action in these joints. The research for this paper focuses on measuring and predicting the praying forces for square hollow structural sections (HSS) with bolts surrounding all four sides of the hollow section member. Since the prying forces are of primary interest in this project, the bolt forces are monitored using an ultrasonic bolt gauge which ensures very precise measurements during the tests. The experimental study consists of six specimens with three different bolt arrangement and two different flange-plate thicknesses. The results of both these tests and earlier tests on the same subject are compared with existing design formulae and analytical models. Depending on the number of bolts, bolt configuration and flange thickness, tentative recommendations are give for the future design of flange-plate connections between square hollow sections bolted on all four sides.

Spliced members are a common type of structural connection such as in connections of truss segments of long-span truss. A convenient way of splicing hollow section members consists of a connection with flange-plates, shop-welded to the ends of the members which are then field-bolted together. Difficulties arise in estimating the static strength of these splices due to the unpredictability of prying forces in the bolts. Prying forces occur if the flange-plates lever against each other due to deformation of the plates under tensile loading. Hence, the bolt loads are increased by these prying forces, which results in an early failure of the splice. Although a lot of research on the phenomenon of prying has been published, most of the studies are restricted to prying of T-sections or prying in the tensile region of beam-to-column end-plate connections.

ISOPE-I-99-351

The Ninth International Offshore and Polar Engineering Conference

This paper presents in a first part, the operational feedback of the SIRENE self positioned free swimming vehicle tele-operated through a bi-directional long range acoustic communication system. This vehicle, designed by IFREMER for the management of benthic loads on the sea floor, had demonstrated the possibilities of deep sea Intervention ( Up to 3000m depth) with AUV. The SIRENE experience leads a team driven by the CYBERNETIX company In collaboration with IFREMER (France) to propound a new concept of intervention in the scope of new deep sea challenges for the oil offshore industry. This new concept named SWIMMER Sub-sea Works, Inspection and Maintenance with Minimum Environment ROV, will be introduced taking into account the SIRENE experience and the industrial requests.

ISOPE-I-99-184

The Ninth International Offshore and Polar Engineering Conference

SPE Disciplines:

In some past discussions in literatures, the roots of the bending differential equation of a ring-stiffened cylindrical shell acted under the homogeneous water pressure were taken to be complex numbers. In this paper, the existence of five cases was verified using model experiment, theory and a series of computation. The paper shows that it is unreasonable to use internal pressure test of the submarine pressure hull specified by the current rules for submarine construction as the pressure corresponding to the extreme depth of submergence. The errors of stress caused by the internal pressure test would be dangerous, and the internal testing pressure should be raised.

The pressure hull structure of submarines is usually described as a series of ring-stiffened cylindrical shell. There are tour roots of the characteristic equation derived from the bending differential equation of a ring-stiffened cylindrical shell acted under the homogeneous water pressure. These roots may be real, or complex numbers, or purely imaginary. Although some of these possible forms of roots were recognized in theory, only one possible root corresponding to the case r

ISOPE-I-99-443

The Ninth International Offshore and Polar Engineering Conference

A very few literature exists up to now analysing force development acting on perforated caisson and presenting liable tools for determination of design parameters. This paper based on 2D model tests presents quantification of the distribution of forces bearing on the different faces of the caisson and shows effect of phase difference in development of total peak force. Comparison is made between data of model tests and results obtained by calculation of total peak forces using Takahashi method. Field measurement recorded on Dieppe breakwater give an illustration of the force development mode on the structure. INTRODUCTION A very few literature exists up to now in the particular field of analysis and determination of horizontal forces acting on perforated caisson. The present work, performed within the framework of MAST III- PROVERBS, is based on 2D model tests as well as on feed back from field measurement at Dieppe (France). It aims to bring a contribution in the improvement of the common knowledge and design of this kind of structure. 2D MODEL STUDY OF HORIZONTAL FORCES Description of 2D model tests Model tests were achieved in 25 m long wave flume (0.80m x 1.00m x 25.0m). The model is a perforated caisson, representing Dieppe breakwater scaled at 1/25, put on a flat bottom. Chamber width is B= 54 cm and perforations are due to circular holes φ 40 mm giving total porosity of perforated wall ε = 0.28. Seven wave characteristic sets were applied using monochromatic wave generation. Wave periods vary from ls to 7s (5s to 35s in prototype) and wave heights vary from 2 cm to 20 cm (0.5 m to 5.0 m in prototype). Two water depths were used in the wave flume d= 40 cm and d= 50 cm (respectively 10 m and 12.50 m in prototype).

ISOPE-I-99-329

The Ninth International Offshore and Polar Engineering Conference

A three dimensional, nonlinear, dynamic finite element analysis (FEA) technique has been developed for computing the time domain response of a semi-submersible structure to ocean wave and current loading using a modified Newmark algorithm. Airy wave theory is used to characterize the ocean model. Morison''s equation is used to develop the fluid loading on the structure. A threedimensional finite element model has been developed for a very large, modular, articulated semi-submersible platform of interest. This platform is a candidate concept for a Mobile Offshore Base. The full three-dimensional response is computed and parameters of interest are reported for various sea states and wave incidence angles. The results are compared with experimental data from physical scale model hydrodynamic testing. Agreement of the computed results with experimental data is found to be very good, but the internal forces required to maintain integrity of the intermodule connections are found to be very high. In order to examine techniques for reducing the intermodular connection forces, studies were conducted to determine the sensitivity of the predicted structural response to variations in connector structural stiffness on the internal forces of connection, the natural frequencies, and the mode shapes of the finite element model. The results represent an original approach, based upon a commercially available FEA code, which conclusively establishes the importance of flexibility in intermodule connector design for control of internal forces of connection, natural frequencies and mode shapes in large, articulated ocean structures. The work described was performed under the Mobile Offshore Base program supported by the Office of Naval Research.

Certain economic, social and military changes in the world have created interest in the concept of large floating structures. Such platforms have been considered for uses including airports, factories, fish farming facilities, and relocatable military bases.

ISOPE-I-99-115

The Ninth International Offshore and Polar Engineering Conference

Industry:

- Government > Military (1.00)
- Energy > Oil & Gas > Upstream (0.69)

SPE Disciplines:

Kumakura, Yasushi (Kinki University) | Takanashi, Masahiro (Ishikawajima-Harima Heavy Industries Co.) | Fuji, Akio (Ishikawajima-Harima Heavy Industries Co.) | Kitagawa, Masaki (Ishikawajima-Harima Heavy Industries Co.) | Kobayashi, Yuki (Ship Research Institute)

Corrosion fatigue tests were carried out in synthetic seawater in order to clarify the temperature effect on the corrosion fatigue strength of coated steel and the effectiveness of coating films of welded joints for the corrosion fatigue strength, which ship classification societies'' rules stipulate. Specimens, made of NK class KA32 TMCP steel plate in 10mm thickness had the notches of stress concentration factor 2.0 at both sides to simulate the stress concentration due to welding at the welded joints. They were exposed to air for 20 days, sprinkled water twice a day to simulate the shipbuilding practice, made surface preparation and finally coated with tar epoxy resin paint. As the results of the tests, the fatigue strengths of the coated specimens in seawater were almost equivalent to those of non-coated ones in lower cycle region, while they were improved in higher cycle region.

1. INTRODUCTION

Ocean is the severest environment for steel structures. Especially the ballast tanks in ships are subject to the worst corrosion circumstances by the repeat of full loading of water ballast on the voyage to the loading port and empty loading on the return voyage. To prevent the corrosion of steel structures of ballast tanks, heavy duty painting, mainly of tar epoxy resin painting, is required by the classification rules. In addition to the corrosion, ship structures receive cyclic wave loads during voyages. For these reasons the structures of ballast tanks must be designed and evaluated from the view point of corrosion fatigue strength. So far many researchers have studied the effect of coating on the corrosion of steel plates. These studies have been concerned with mainly deterioration of coating films, by measuring alternating impedance, adhesive forces or by bending tests (SR182, 1981), (SR201, 1990).

ISOPE-I-99-360

The Ninth International Offshore and Polar Engineering Conference

air, coating, coating film, corrosion, corrosion fatigue, corrosion fatigue life, crack, effect, fatigue, Fatigue Strength, film, film thickness, H2S management, machine learning, oilfield chemistry, platform design, seawater, specimen, steel, stress, sub-sea system, subsea system, temperature, test, Thickness

Industry:

SPE Disciplines:

In limit equilibrium methods (LEM), all methods employ the same definition of the safety factor as a ratio of the shear strength of the soil to the shear stress required for equilibrium, employing certain assumptions with regard to equilibrium. Also, in the conventional finite element methods of analysis, the minimum safety factor is obtained assuming certain slip surfaces after the stress states are found. Although the stress states are obtained from the finite element method (FEM), the slope stability analysis follows the conventional method that assumes a potential slip surface. In this study, a FEM slope stability analysis is developed to locate the slip surface by tracking the weakest elements in the slope based on the local safety factor considering the magnitude and direction of the shear stress. It has also been applied to compare with the slip surfaces predicted by LEM methods. A computer program has been developed to draw contour lines of the local safety factors automatically. This method is illustrated through a simple hypothetical slope, a natural soil slope, and a dam slope. The developed method is compared very weel with the conventional methods, with slightly lower low global safety factors.

Slope stability analysis methods, can be classified into two general methods: the limit equilibrium method and the finite element method. The limit equilibrium method is utilized without a prior knowledge of the location and geometry of the slip surface. A potential slip surface, either circular or log-spiral geometry or others, is then assumed and the minimum safety factor is found through iterative search. In LEM, the number of available equations is smaller than the number of unknowns. Therefore, all limit equilibrium methods of slope stability analysis need to employ assumptions to render the problem determinate.

ISOPE-I-99-071

The Ninth International Offshore and Polar Engineering Conference

Oilfield Places:

- North America > United States > Texas > Brown Oil Field (0.89)
- North America > United States > Nebraska > Anderson Oil Field (0.89)

SPE Disciplines:

- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (0.68)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.34)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid management & disposal (0.34)

Residual stresses are developed as a result of manufacturing and fabricating a steel structure, and can have a significant influence on weld cracking, strength and in-service behaviour of welded structures. In the present study a specially designed test rig has been used for assessment of residual stresses for given welding conditions characterized by the peak temperature, Tp, and cooling time, Ats/s, of the thermal cycle. A high strength low alloy quenched and tempered steel with specified minimum yield strength 690 MPa is examined. In fracture assessment of structures in the as-welded condition, the tensile residual stress is assumed to be equal to the room temperature yield strength of the material. This assumption reduces the possibility to exploit the strength benefit of QT steels and is shown to be very conservative in the case of these materials, where the residual stress level is considerably lower than the base material yield strength.

The advantages of weldable high strength steels (yield strengths exceeding 500 MPa) are being quickly recognized by the offshore industry, and the amount of high strength quenched and tempered steels used has increased significantly in recent years. This is a result of the general trend to save weight and thus to reduce costs. The''principal application in offshore construction has been in the fabrication of jackups, where legs are sometimes fabricated from steels with yield strength >700 MPa. Steels for pipelines are increasing in strength with X70 being commonly used and with significant interest being shown in X80 (HY80) and X100 (HY100) steel grades to reduce pipeline project costs (Hillenbrand, Niederhoff, Amoris, Perdrix, Streisselberger and Zeislmair, 1997). The problems experienced are connected to the HAZ strength and toughness properties, and the fracture toughness of the weld metal intended to overmatch the base metal. In addition, welding causes residual stresses.

ISOPE-I-99-364

The Ninth International Offshore and Polar Engineering Conference

The present study was performed in order to understand the effect of soil compressibility and crushability on the monotonic and cyclic undrained strength of soils. Aio sand which is a beach sand from Yamaguchi prefecture in the south-west of Honshu in Japan was used for triaxial tests preparing with a particle size distribution of 2mm down to 74gin. The triaxial specimens of 50ram diameter and 100ram height were air pluviated to a relative density of 80%. The Samples were isotropically consolidated at mean normal effective stresses of 0.1MPa, 1MPa, 3MPa and 5MPa. Monotonic triaxial shear tests were carried out at confining pressures of 100kPa, 1Mpa, 3MPa and 5Mpa while cyclic triaxial tests were carried out at confining pressures of 100kPa, 3MPa and 5MPa. Further many sieving tests were performed at several stage of shearing by terminating the triaxial tests to determine the degree of particle breakage. The fines content was increased due to particle crushing even during undrained shear process in which the effective stress decreased. It was noted that the undrained shear behaviour was greatly dependent on the particle crushing of sands.

In 1964 during the Niigata earthquake there was widespread damage due to liquefaction. This led to a large research effort on the liquefaction properties of silica sands. However in 1995 during the Great Hanshin Earthquake serious damage occured to port and harbour facilities such as Kobe Port Island and Rokko Island. Both of these were areas of reclaimed land filled with a crushable residual granite soil, Masado. In 1997 during the Kagoshima-ken Hokuseibu earthquake, the liquefaction of a crushable volcanic soil, Shirasu, was observed. Further many sieving tests were performed at several stage of shearing by terminating the triaxial tests. Variation of particle distribution curve was observed in both consolidation and shearing process.

ISOPE-I-99-118

The Ninth International Offshore and Polar Engineering Conference