bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure And Possible Petroleum Traps Of Lower Cook Inlet, Alaska
Authors: Fisher Michael A.
Published: October 2008

The regional structure of lower Cook Inlet is a large northeast-trending syncline that extends the width of the inlet. The syncline, which involves Mesozoic and Tertiary rocks, is divided into two oppositely-plunging synclines at the latitude of Augustine Island by the Augustine Seldovia arch. This arch trends east-west, transverse to the axis of the lower Cook Inlet basin, between Augustine Island and the Kenai Peninsula near Seldovia. A number of anticlines have their axes parallel to the basin axis and intersect the arch at oblique angles. Domical structures could be formed where the two structural trends intersect, providing a possible setting for petroleum entrapment. The northeast-trending anticlines also may be structural traps. Seismic data reveal a number of unconformities in the offshore area. In particular, a regional angular unconformity interpreted to separate Mesozoic and Tertiary rocks extends northeastward along the southeast coast of lower Cook Inlet. Truncated strata beneath this unconformity may contain combined structural and stratigraphic traps.

INTRODUCTION

Lower Cook Inlet is the southern half of an intermontane basin in south-central Alaska (Fig. 1). On the southeast side of the inlet are the towns of Homer and Seldovia, along the northwest coast are Cape Douglas; Augustine Island, and the Iniskin Peninsula.

Two seismic surveys that provide public information were conducted in lower Cook Inlet. In July, 1975, the U. S. Geological Survey contracted with Western Geophysical, Inc. to collect 480 km of common-depth-point (COP) seismic data using a 2,700-m, 72-channel streamer, Aquapulse guns, and DDS-888 digital instruments. The grid of seismic lines is about 30 km square. A combined Raydist/RPS navigation system located shot seismic data was processed by Petty-Ray Geophysical, Inc. Copies of the 36-fold final stack sections and shot point maps are available to the public through: National Geophysical and Solar Terrestrial Data Center, Code D-62l, Boulder, CO, 80302.

A second seismic survey was conducted in July 1976 aboard the R/V SEA SOUNDER, a vessel operated by the U. S. Geological Survey. A 30-kiloJOUle sparker system obtained data along track lines that form a grid about 15 km square. Some sparker lines are in the same locations as the CDP lines. Although the sparker data has about one-tenth of the sub bottom penetration of the COP data, axes of structures in Tertiary rocks can be clearly seen. The COP lines are too widely spaced to define the extent of structural axes, but show the regional configuration of deep strata beneath lower Cook Inlet.

Three seismic horizons were correlated throughout the grid of COP lines; all three are too deep to be seen on the sparker data. In order of increasing depth, the horizons are labeled A, B, and C. The A-horizon is believed to be at the base of Tertiary strata; the B horizon might be at the base of Upper Cretaceous strata; the C-horizon may be near the base of Upper Jurassic strata.
Extending Seismic Design Provisions For Buildings To The Design Of Offshore Structures
Authors: Sharpe Roland L. , Newmark Nathan M.
Published: October 2008

The philosophy and background of seismic design provisions for buildings are discussed. The applicability of design assumptions and provisions used for buildings to extremely tall, slender, and flexible offshore structures is reviewed. Offshore structures are much bigger in plan than most buildings and do not have a common foundation. Hence they may respond in torsion as well as translation to seismic motions. Moreover they are surrounded by water that causes different types of actions and response to dynamic inputs. The significance and possible effects on offshore structures of major earthquake motion characteristics are presented. Areas that require detailed study are described.

INTRODUCTION

Earthquakes are of special interest because they can affect most components of a structural system and the equipment supported thereon. Earthquakes occur at irregular time intervals and transmit transient dynamic ground motions which can induce large forces in man-made facilities. The response of structures and their contents to such dynamic motion is a very complex phenomenon.

There has been a tendency in most parts of the United States to view earthquakes as a California problem. However, over 70 million people in 32 states are subject to major and moderate earthquake risks, that is, earthquake motions with effective peak ground accelerations exceeding 0.l0g. If it is assumed that the seismic design regionalization maps recently developed by the Applied Technology Council (ATC) can be extended offshore, about 41 percent of the East Coast, 80 percent of the West Coast excluding Alaska, all of the Gulf of Alaska including the Aleutians, the Bering Sea coast up to about 60 degrees north latitude about one half of Hawaii, and much of Puerto Rico are subject, to effective peak ground accelerations exceeding 0.10g.1

Until recently few offshore structures have been built in active earthquake areas. Most offshore structures have been constructed in the Gulf of Mexico, a re1atively Quiescent seismic area. A few structures have been built off the southern California coast and in Cook Inlet, Alaska. For the Cook Inlet structures, the forces exerted by ice packs were more severe than those from earthquakes. The design of most of the southern California structures followed the Uniform Building Code (UBC) requirements for buildings, with each company using earthquake engineering consultants, as appropriate.

The increasing energy crunch and impending future shortages have sparked an upsurge in interest in developing the potential oil reserves existing in the outer continent shelf (OCS). Activity is largely centered in the Gulf of Mexico, southern California coast, Gulf of Alaska, and the mid-Atlantic coast. Of these areas, those off southern California and the Gulf of Alaska are in seismically active areas. The earthquake problem is not unique to the United States, and offshore developments near New Zealand, Indonesia, and the Philippines are also subject to major earthquake motions.
A One-Hundred-Ton Oil Recovery Vessel for Bantry Bay
Authors: Neal R.W. , Bianchi R.A. , Marcus E.W.
Published: October 2008

As part of a world-wide program. to provide complete oil-spill response capabilities to its operating facilities, the Gulf Oil Corporation has acquired a newly developed oil recovery ship for its deep-water oil terminal in Bantry Bay, Ireland. Besides requiring a highly effective oil recovery unit, Gulf also required a ship to patrol the waters near Whiddy Island, where the terminal is located, and periodically to patrol the full length of Bantry Bay, a round trip of about 50 miles.

Located on the southwest coast of Ireland, the Bay is exposed to the North Atlantic Ocean, and sea conditions are frequently severe the year round. In winter, rough to high seas (5 to 20 feet in height) are at a maximum., occurring 33 to 67 percent of the time. During spring, rough seas are at a minimum., but still occur 18 to 24 percent of the time.

Half-scale oil recovery tests were conducted in Boston Harbor and at EPA I s oil spill control test facility. A description of the facility, the procedures used and surface and underwater photography of several of the tests -are presented in the paper.

Seakeeping properties of the ship designed for use in Bantry Bay, Ireland, were investigated using the "5-D Seakeeping Program.". The program. was run for nine wave spectra which fully covered the range of sea conditions in which the vessel could expect to operate.

The vessel christened the "Bay Skimmer", is a fully equipped, 68 foot, 100-ton ship designed to patrol at speeds up to nine knots and to recover oil up to three knots.

INTRODUCTION

Gulf Oil Terminals (Ireland) Ltd., operates a deep-water oil terminal located on Whiddy Island in Bantry Bay, Ireland. Very large tankers (VLCC?s in excess of 250,000 DWT) unload crude oil from. the Middle East here, and smaller tankers are loaded for shipments to refineries throughout Europe.

Bantry Bay is located on the southwest coast of Ireland, which is characterized by bold mountainous peninsulas. Bantry itself is a minor port, significant primarily as a local fishing harbor and port of call for small. coastal vessels. The entire area, which is picturesque and unspoiled, is becoming increasingly attractive to tourists.

The Gulf terminal was built in 1968. Great care was taken to assure that storage tanks were strategically placed to avoid visual "pollution" altogether. Operations of the terminal have been conducted with equally great care to prevent accidental oil spills, and an excellent safety record has been established. Nevertheless, because of the number and size of the ships handled here, Gulf selected Bantry as one of the terminals worldwide to be equipped with a complete oil-spill response capability.

After evaluating several alternatives, Gulf selected the type of skimmer which it felt would be best suited to the needs in Bantry Bay. An oil recovery ship, which is the subject of this paper, was then developed to meet the specific requirements of this location and service.
Simultaneous Passive And Active Microwave Observations Of Near-Shore Beaufort Sea Ice
Authors: Campbell W.J. , Gloersen P.J. , Zwally H.J. , Ramseier R.O. , Elachi C.J.
Published: October 2008

The use of active and passive microwave imagery in combination is the optimum way to observe the morphology and dynamics of near shore ice. Active and passive microwave data from aircraft that are described in this paper are also compared to the ESMR (Electrically Scanning Microwave Radiometer) imagery of the Nimbus-5 satellite. The information thus obtained shows how the data to be received from the SAR (Synthetic Aperture Radar) and SMMR (Scanning Multichannel Microwave Radiometer) and on Seasat A and Nimbus G have the potential of providing a vastly increased understanding of the near shore ice of the Beaufort Sea.

BACKGROUND

The current need for sea ice information has occurred at a time of rapid-evolution of both remote sensing platforms and sensors. These timely technical advances are beginning to eliminate the observational barriers that have limited our knowledge of a natural phenomenon existing in areas that are dark and/or cloud-covered much of the year. Furthermore, since sea ice undergoes large spatial variations on short time scales, the new sensing techniques are for the first time acquiring the sequential synoptic observations needed for cause and effect studies.

Considerable emphasis has in recent years been placed on the microwave remote sensing of sea ice because it offers the possibility of an all-weather, day-or-night, capability. Both passive and active microwave remote sensing techniques have been explored. An overview of these activities has been given in Campbell et ala (1975). Early work in this area utilized passive microwave techniques since such techniques were the first to be incorporated on board earth-viewing satellites.

The most important series of aircraft flights which demonstrated the feasibility and usefulness of ice observations by means of passive microwave sensors were those that occurred during the NASAAIDJEX (Arctic Ice Dynamics Joint Experiment) joint program. A series-of three AIDJEX pilot field experiments were performed during the springs of 1970, 1971 and 1972 in the southern Beaufort Sea. During each of these experiments, the NASA CV-990 "Galileo I " performed a variety of flights ranging in altitude from 150 m to 11 km. A wide variety of visual and infrared sensors were operated in addition to an imaging radiometer operated at a wavelength of 1.55cm and fixed-beam radiometers operated at wavelengths of 0.81, 2.8, 6.0, and 2lcm.

The 1970 data (Wilheit et al, 1972) showed that it was possible to distinguish sea-ice from liquid water both through the clouds and in the dark. This finding was useful because it pointed the way to an "all-time" ability to observe leads and polynyas. These data also showed that strong microwave emissivity differences occur on the ice surface itself. However, the lack of sufficient ground truth data prevented a determination of the reason for these differences.
New Marine Seismic Source Of The Gas Exploder Type
Authors: Reed Dale H. , Hardison Jack E.
Published: October 2008

This new marine seismic source is a gas exploder of the DINOSEIS ® class. The principle of cavitation is built upon to obtain an improved acoustic output. Previous sources of this general type were designed to produce a direct compressional pulse while suppressing cavitation. In the new device a contained detonation drives a single plate through the water at high velocity, forming a cavitation bubble. The natural collapse results in a sharp acoustic pulse with several bar-meters peak amplitude. Such a pulse is ideal for seismic surveys. Several sources can be combined in an array for greater penetration.

Underwater photographs are displayed to illustrate the mechanism of pulse generation by bubble collapse. Calibrated far-field acoustic signatures are shown. In addition, waveforms from a downhole geophone in a Gulf of Mexico well velocity survey are displayed. A preliminary single channel marine reflection survey is shown.

INTRODUCTION

Marine seismic sources of the gas exploder type have traditionally been designed to create a compressional pulse from detonation of oxygen propane mixtures. This process requires rapid volume-acceleration and usually results in relatively low peak pressures. A study of the literature on cavitation shows that high peak pressures are obtained when vapor bubbles collapse in water. Peak pressures in excess of 104 atmospheres have been reported.1

Building on the concept of cavitation we have designed, built, and tested a new broad-band seismic source. Figures 1 and 2 show pictures of current working models.

BASIC DESIGN

Cavitation of water is a well known phenomenon. Usually cavitation happens in such a way that it is destructive and undesirable. For example, pumps and propellers are designed to avoid cavitation.

Since water cannot sustain stress in tension, it will change to vapor at low pressures. Accurate theories of cavitation do not exist, but it is fairly certain that dissolved gases come out of solution and form nuclei for water vapor bubble growth. It has long been observed that when the ambient water pressure returns to normal an inward flow collapses the bubble with little or no rebound. Coincident with this collapse a transient pressure of extremely high magnitude is created which radiates as a sound wave of high intensity.

If we assume a vapor or cavitation sphere in a body of water, we can calculate the potential energy. Figure 3 shows this energy, which on collapse is suddenly converted into compressive force and acoustic radiation. The conversion is quite efficient and offers an attractive method for seismic wave generation.

The concept for creating a large cavitation bubble is shown in Figure 4. A piston and cylinder is arranged so that the explosion of a propane-oxygen mixture drives a plate rapidly through the water, leaving a cavity behind. As will be shown later, a second pulse is generated as the piston rebounds from compression in the air box.
On The Strength Of New Composite Steelconcrete Material For Offshore Structure
Authors: Matsuishi M. , Nishimaki K. , Takeshita H. , Iwata S. , Suhara T.
Published: October 2008

The authors have developed a new composite steel-concrete material for the strength members of huge offshore structures, where concrete is placed between steel plates. This paper contains the results of both experimental and theoretical investigations into the strength of the new composite material. Experiments under static and repeated loadings were carried out. Four types of test models of the composite material were subjected to shear, bending or combined shear and bending. It was found that the ultimate strength of the composite material is very high and it can absorb a great deal of energy at failure. A method for the ultimate strength analysis of the composite material is developed. The calculated results are in good agreements with experimental ones. Nonlinear analysis is carried out using the finite element method. In the analysis, the material nonlinearities of both concrete and steel are fully taken into account; the propagation of a crack in concrete caused by tension, plastification and crush of concrete by compression, and plastification of steel plate. Geometrical nonlinearity caused by gaps between concrete and steel is, also considered. The analysis accurately represented the behavior of the composite material under tests.

The new composite material is found to be desirable for the construction of offshore structures because of their excellent properties; large energy absorption and strength carrying capacity.

INTRODUCTION

The utilization of concrete and/or composite steel-concrete material for offshore structures gives the advantages of low initial cost, low maintenance cost and good impact resistance. Many projects using concrete are in various stages of design for offshore structures of near future such as an offshore power station.

A huge offshore structure, if made of steel, necessitates a great deal of dead load to offset its big bouyancy, whether it is of the floating type or the gravity type. The concrete may be employed as ballast and strength members in such an offshore structure. Drawbacks of concrete associate with low tensile strength and low ductility. It is difficult to secure watertightness, once concrete cracking develops in an offshore structure used in deep water, where the pressure is very high. And this may cause serious troubles. If ordinary composite steel-concrete material, such as reinforced concrete or prestressed concrete, are employed, crack starts on the surface of concrete by bending. Drawbacks of concrete require a design with an excessive margin as the exact estimation of the external forces acting upon an offshore structure is nearly impossible.

The authors have developed a new composite steel-concrete material for offshore structures to cover up the various drawbacks of the concrete. The new composite material endures large deformation and absorb a great deal of energy at failure, because the steel plate with high strength and ductility suppresses the development of surface cracks.
Procedure For Analyzing The Fatigue And Slow Crack Growth Behavior Of a Ship Structure
Authors: Marchica Nicholas V. , Beach Jeffrey E.
Published: October 2008

A procedure for analyzing the fatigue and slow crack growth behavior of any ship structure is presented. Particular emphasis is placed on high performance ships such as hydrofoils, surface effect ships, and planning craft. Stress analyses determine the allowable fatigue design stress. A fatigue load spectrum for any particular detail is determined using in-service trials data if available or analytical techniques. An operating area analysis is performed establishing the percentage time the ship will be operating in various sea states. A fatigue analysis, using laboratory data, is performed as if the ship was operating 100 percent of the time in each sea state, the results indicating which sea states caused the greatest damage to the structure. The fatigue life of the critical area is found by summing the life predictions in each sea state based on the operating area analysis. A slow crack growth analysis, based on laboratory data, is performed using linear elastic fracture mechanics. The results of the procedure are used to determine if the structural detail analyzed should be accepted or redesigned.

INTRODUCTION

Ship structures, particularly hydrofoils, surface effect ships, and planning craft, are being built of new high strength-to-weight materials. Unfortunately, these materials are susceptible to fatigue and slow crack growth that may cause premature structural failure. An analysis approach or method is necessary to minimize this risk and insure the structural integrity of the ship structure.

This paper presents a procedure for analyzing the fatigue and slow crack growth behavior of a ship structure. A stress analysis is performed on a potential fatigue critical area of the structure to determine the allowable fatigue design stress. A fatigue load spectrum for any particular detail is determined using in-service trials data if available, or using analytical techniques. An operating area analysis is performed based on the ship's assumed deployment area, establishing the percentage time the ship will be operating in the various sea states. A fatigue analysis, using laboratory data, is performed as if the ship was operating 100 percent of the time in each sea state, the results indicating which sea states caused the greatest damage to the structure. The fatigue life of the critical area is found by summing the life predictions in each sea state based on the operational spectrum. A slow crack growth analysis, based on laboratory data, is performed using linear elastic fracture mechanics. The results of the procedure are used to determine if the structural detail analyzed should be accepted or redesigned.

STRESS ANALYSIS

A stress analysis is first performed on a critical area of the structure where fatigue and slow crack growth are of concern. This stress analysis may take many forms from the most simplified strength-of material approach to a sophisticated finite-element analysis or photoelastic analysis.
The Dynamic Behavior Of Mooring Lines
Authors: van Sluijs M.F. , Blok J.J.
Published: October 2008

In this paper the results are presented of ＿a model study into the behaviour of anchor lines as used in the offshore mooring of a wide variety of floating structures. For this study model tests have been carried out with a buoy moored to four chains. The effect of model scale, pre-tension in the lines, wave height and wave period on the line tensions is discussed. Special attention is given to the dynamic behaviour of the mooring system, resulting into higher tensions than would follow from-calculations based upon the static catenary theory. The existence and significance of dynamic effects is confirmed by the results of forced oscillation tests with model anchor-chains in calm water.

INTRODUCTION

For offshore floating structures, which are exposed to environmental conditions, station keeping above a fixed point is an important requirement. To resist the resulting external forces these structures are, in the majority of cases, anchored to the sea bottom. It will be clear that a proper design of the anchoring system is of great importance. Inaccuracies in the design of the system and in the estimation of line tensions can have serious consequences [1].

In analysing forces and tensions in anchor lines a static and a dynamic part can be discerned. The static part covers the calculation based upon the classic catenary theory, a method which is generally applied in the design of systems capable to balance the external forces- [21 and [3]. According to Alexandrov [4], this procedure yields reliable results. Also field tests have indicated that the results of such static calculations conform very well to the measurements [5], which implies that cable dynamics have a negligible contribution to the total forces.

The approximation of anchor line forces based on statics is generally valid for lines attached to structures, whose motions come close to the static case. To meet this condition it is essential for the structure to have large natural periods of motion and small amplitude responses in the frequency range of wave components. For certain structures, however, the behaviour in waves is much different. Owing to small natural periods the relatively high :frequencies of the wave components cause large amplitudes of motion.

Recent model tests in waves, carried out at the Netherlands Ship Model Basin, showed that the resulting behaviour of the mooring lines may no longer be approximated statically. Larger mooring line tensions were observed than would follow from static catenary calculations, particularly for the weather-side lines.

Dynamic effects may be analysed mathematically through application of a finite difference method, [6], [7] and [8]. Although some insight might be obtained in this way, the sensitivity of the dynamic effect to the various mooring line parameters is still not fully explained.

Therefore, two series of systematic model experiments were carried out. The first series comprised tests in waves with a cylindrical buoy moored to four chains.
The Evolution of the Earth's Crust and Sedimentary Basin Development
Authors: Green A.R.
Published: October 2008

The earth's crust is a thin, dynamic shell that changes in both thickness and composition through time. It is postulated that the changes that alter the crust are primarily the result of subcrustal processes and lateral interactions of crustal plates. The type of crust that underlies a sedimentary basin determines the physical framework, stability, manner of structuring, and conditions of sedimentation and environment throughout the evolution of the basin. Thus, as sediments are deposited, they record the tectonic history of the basin. These stratigraphic data can be used to develop conceptual, genetic models that put the evolution of oceanic, continental, and transitional types of crust into perspective. An orderly cycle of crustal evolution is proposed which suggests that oceanic crust is thick end and continental crust is thickened and thinned by a number of natural processes. The resulting transitional crustal types, which represent intermediate steps in the continuum, occupy a realm between thin, basic oceanic crust and thick, acidic continental crust. These transitional, somewhat unstable crustal types host most of the world's sedimentary basins. An attempt is made to step back from the detail of the complex interplay involved in the process of crustal genesis and sedimentary basin development and' look at the overall natural system. A set of hypothetical, genetic models depicting the proposed origin of various crustal types is presented so that geophysical data can be compared and tested against them.

THE CRUSTAL SETTING OF SEDIMENTARY BASINS

Sedimentary deposits greater than 2000 meters thick accumulate in depressions within the major continents or adjacent to their margins (Fig. 1). Basins within the major continents contain a large percentage of Precambrian, Paleozoic, and Mesozoic sediment, which furnishes a record of crustal evolution during these earlier periods of the earth's development. Some of these older rocks have been metamorphosed to such a degree that they can no longer be considered part of the sedimentary section, but rather are more closely related to the underlying crystalline crust. Basins on the marginal shelves, slopes, and rises of the Atlantic and Indian Oceans contain sediments of Mesozoic and Tertiary age and form some of the thickest sediment accumulations in the world. Most of the sedimentary basins around the margins of the Pacific Ocean have formed more recently and furbish valuable clues concerning the Tertiary crustal history of that part of the world. Indeed, many of the Pacific margins are presently in an active stage of basin formation and provide modern analogs to ancient mechanisms of crustal evolution.

Most of the world's sedimentary basins overlie crustal types that are neither purely continental nor purely oceanic in terms of thickness and composition. They generally develop upon thinned continental crust or upon accreted, constructed continental crust (Fig. 2).
Application Of Critical State Soil Mechanics To The Prediction Of Axial Capacity For Driven Piles In Clay
Authors: Kirby Robert C. , Wroth C. Peter
Published: October 2008

A companion paper by Esrig et al {1977} describes the initial development of a general effective stress method for the prediction of axial capacity for driven piles in clay. A dominant physical characteristic of driven piles in clay is a zone of severely remolded soil around the pile. The available shear resistance of the soil in the remolded zone controls axial capacity for driven piles in clay. This paper summarizes how critical state soil mechanics was used during an initial study to describe the engineering properties and stress conditions of the soil in the remolded zone.

It is assumed that the reader is not familiar with the concepts of critical state soil mechanics. Those concepts relevant to the pile problem are briefly explained and procedures for estimating the necessary soil parameters by direct testing, or indirectly from correlations with index tests, are presented.

The changes in stress during pile driving and reconsolidation after pile driving are illustrated by stress paths.

INTRODUCTION

A companion paper by Esrig et al {1977} describes the initial development of a general effective stress method for the prediction of axial capacity for driven piles in clay. As noted in that paper, several distinct zones can be identified in the vicinity of a driven pile in clay. These zones are illustrated in Fig. 1. A zone of severe remolding due to pile driving encircles the pile as indicated by Zone A. The soil in this zone has experienced large displacements and has been "turned upside-down" by the pile driving operation. For displacement piles, the zone of severe remolding extends to at least 1.4 pile radii from the center of the pile based on volume considerations.

Outside the zone of severe remolding, the soil has been stressed by the increase in volume caused by pile installation. In this zone {Zone B}, the soil accommodates the pile installation by relatively small radial displacements. The soil in Zone B may become overstressed but it is not "turned upside-down" by the pile driving process. Soil displacements due to pile driving are influenced by the ground surface to some limited depth; below this depth, the soil displacements are in the radial direction only. Near the bottom of the pile the displacements are influenced by the pile tip.

An essential step in the development of a general effective stress method for prediction of axial capacity, of piles driven into clay, is the prediction of the effective stress in Zone A immediately after driving. This requires the use of a model for soil behavior which adequately describes the behavior of soils at large strains. The concepts of "critical state soil mechanics" {Schofield and Wroth, 1968} were developed to permit prediction of the behavior of soils at all strains but the cornerstone of this model is the state of stress at large strains.
Environmental Conditions on the Continental Shelf off West Greenland
Authors: Nielsen Hasle A. , Dietrich J.A. , Fabricius J.A.
Published: October 2008

Petroleum exploration activities started on the Greenland Continental Shelf in 1975 and intensive data collection programs on hydrographic, metrological and ice conditions have been carried out during the summer and fall seasons 1975 and 1976.

The paper describes the environmental conditions in the Davis Strait with emphasis on the concession areas between latitudes 63°and 68°N

The wave climate which is strongly correlated with the storm conditions was found to vary with the location and the seasons with the most severe conditions occurring late fall. During 1975–76 the maximum recorded wave heights was 6,8 m with corresponding wave periods of Tz = 9,5 sec.

The currents on the shelf were found to be governed by a general northward circulation of water and tidal current. The tidal currents vary geographically from weak diurnal currents to strong semidiurnal currents. Variations in currents were also found with the depths. Maximum current velocities were in 1975–76 measured at 80 cm/sec and the daily net drift speed was typically 10–20 cm/sec.

The ice conditions are governed by the "Vestis" and icebergs of glacial origin. The app. one meter thick Vestis" moves southwards during the fall and covers large parts of the Davis Strait during winter and spring.

Icebergs are found in many sizes through out the year. They originate mainly from the east and south coasts and from the Disco Bay in the north. The maximum size and draught of the measured icebergs were 8.5 Mt and 50 m, respectively.

INTRODUCTION

Until offshore petroleum exploration began in 1975 only little attention had been paisa to the environmental conditions on the continental shelf in the Davis Strait off West Greenland

Only very limited hydrographic data was found to exist at the concession areas located up to 160 km off the coast between latitudes 63° and 68°N, and data on ice conditions which as the most critical factor for offshore operations in Ghese areas, was also found to be scarce.

In order to provide data on currents, icebergs, ice drift and weather conditions comprehensive environmental data collection programs were therefore carried out in 1975 and 1976 both by the Concessionaires (with Chevron Petroleum of Greenland as operator) and by the Ministry for Greenland. The Programs of the Concessionaires aimed primarily at providing sufficient data for planning and execution of drilling operations and was concentrated on the concession Ares while the programs of the Ministry also emphasized the effects of possible oil spills upon the sensitive arctic environment.

The Ministry's program in 1975 and 1976 was executed by the Danish Hydraulic Institute (DRI) and in 1976 DRI also performed the Industry's Weather ship program. Special iceberg profiling equipment was used in 1976 and a total number of 7 wave rider buoys and 35 Andrea recording current meters were deployed in water depths up to 600 m. The area involve in the 1975 and 1976 measuring programs are shown on Figs. 1-2.
The Neutrabaric Method For One-Atmosphere Working In Subsea Environments
Authors: Ball Kenneth
Published: October 2008

This paper outlines a previously undisclosed and percents developed technique putting men into a working environment on the seabed. In essence it consists of encapsulating equipment to be accessed with one or more pressure vessels, leaving the vessels full of water but depressurizing them to a nominal one atmosphere absolute pressure. The NEUTRABARIC working entwinement so created is a safe, simple, easily controlled and easily purged environment requiring the minimum energy and support facilities for its pupation and maintenance. These factors mean that a submersible with its intently low carried envy capability can be used as a significant economic invention device. In the paper the basic Logia of the NEUTRABARIC method is developed and a typical application to a seabed washed completion is outlined.

INTRODUCTION

It is a characteristic of many of the most significant developments of our time that once one has passed through that phase of "seeing through the problem" -a saying common in educational capsizes on this side of the Atlantic mope so than in Europe or elsewhere - there is a tendency to self-examination on the parrot of the developers through questions such as "why didn't we see that before?" and to skepticism on the part of those with whom the development is shared by observations to the effect that "but that is obvious.? The more obvious it is after definition the more assured one can be that a fundamental step has been made.

So it has been with the NEUTRABARIC method for one atmosphere invention to subsea installation. In retrospect, one can say that the developers of the concept. Intertek Technical Slices Ltd., had lived on the edge of the solution for many years in connection with early developments of manned underwater vehicles and systems; solving specific problems related to certain preconceived overall project definitions; and watching such solutions become eve mope complex as routine development proceeded

No doubt out of frustration caused by the constant mergence of interlinked problems in development of underwater systems a measure of lateral thinking was applied to the situation, stated in its simplest terms, of man working underwater.

So it was that in early 1972, the concept of NEUTRABARIC ACCESS was born out of soon Latah investigation. Since 1972, a quiet but steady application and development of the NEUTRABARIC METHOD OF ACCESS has been proceeding. However, this present OTC is the first time that a formal publication of the concept has been made.

In this paper, it is proposed to build-up the problems, to which the NEUTRABARIC METHOD provides solutions, in a series of stages. The pattern to be followed bears a resemblance to man's history of seeking to work deep under water and it win then be more apparent that the significance of the NEUTRABARIC METHOD is the of basic principle as distinct from time-sequenced problem solving and development.
Concrete Offshore Structures - Behavior Of Full Scale Shells, Hydrostatically Loaded
Authors: Gausel E. , Hafskjold P.S.
Published: October 2008

Findings from a pilot study of the strain development in the first Concept concrete platform, Mobil Beryl A, installed in the North Sea in 1975, were presented at OTC-75, Paper 2405, and OTC-76, Paper 2435.

The Cement and Concrete Research Institute The Norwegian Institute of Technology has continued and intensified these investigations on the third Concept platform, Stat fjord A, which is to be installed this summer(l977).

The objective of the research program is to study the strain development and the relationship between the strains and the external loads.

The conclusions drawn should also be valid for hydrostatically loaded shells in general and not only to this particular type of concrete platforms.

INTRODUCTION

It is a fact that the dimensions of the structural shell elements in the concrete platforms designed for The North Sea have a magnitude beyond our empirical knowledge. The structures are statically indeterminate to a very high degree.

Correspondingly the structural analysis is complex and tedious, especially concerning the construction period, and the question has been raised.

How reliable are these calculations and the resulting reinforcement?

The instrumentations done at Mobil Beryl A and Stat fjord A are steps to approach this problem by direct measurements on full scale structures

The construction methods used made it possible to study the response of clearly defined hydrostatic loads acting on the concrete structures during the construction stages, Fig. 1.

SCOPE OF THE STUDY

When the Cement and Concrete Research Institute started up the instrumentation in April 1974 on the Mobil Beryl A platform, previous instrumentation installed in offshore concrete structures had been confined to the foundation slab in order to monitor the contact pressure between the subsoil and the structure.

The following study mainly comprises the instrumentation started up in March 1975 on the Statfjord A platform.

This instrumentation is located higher up in the structure, and is aiming at the study of the structural behavior of the concrete proper.

The main objective in the research program on Mobil Beryl A as well as Statfjord A was to study the relationship between the measured strains and the external loads. This includes a study of the correlation between the response of the structure and the modulus of elasticity of the concrete determined from standard tests. The loading conditions are in this case unique since the external load is a pure hydrostatic pressure.

Fig. 2 and Fig. 3 indicate the hydrostatic loading during the stages of construction of Statfjord A.
Second End Flowline Connection Without Length Adjustment
Authors: Pras S. , Levallois E. , Gouraud O
Published: October 2008

In order to reduce the cost of flowlines laying and connecting, by decreasing the duration of operations and the size of the supporting vessels, a new method of building the lines onshore, towing them to the site, and connecting both extremites without length adjustment on site has been set up and successfully tested in 50 meters of water depth in the Mediterranean sea, in May 1977.

INTRODUCTION

The french research association Deep Sea Production, formed by the three companies TOTAL - COMPAGNIE FRANCAISE DES PETROLES, INSTITUT FRANCAIS DU PETROLE and SOCIETE NATIONALE ELF-AQUITAINE, is studying the different subjects to be worked out to set up a complete scheme of development of an oil field by water depth beyond the reach of divers. One of these subjects is the flowlines installation.

Previous operations performed by ELF-AQUITAINE in Africa have shown that the cost of flowline laying could be considerably decreased by building the lines onshore, rigging them with pontoons and chains, launching and towing them to the site, instead of using lay-barges.

A flowline being designed to link two sub-marine structures, the last problem to be solved was the second end connection: because of the impossibility to build a line at the exact length necessary to reach the second structure, after having connected the other extremity of the line to the first one, the second end connection was performed by divers, who cut the over-length and installed cumbersome spool pieces. If these time-consuming operations are workable by shallow water, they become rapidly too costly and too hazardous by great depth.

The new way of connection that has been investigated consists of:building the line with a planned over lengthlaying the second end of the line in a well determined abandonment area,pulling this second end towards the subsea structure,locking the pulling head into the structuresettling the pulling head in the right position by hydraulic actuators,establishing the fluid connection by a connector like those used in drilling.

All the points 1 through 5 were experienced twice during the test, an accurate measurement of the position of the flowline hub taking the place of the fluid connection.

PURPOSES OF THE TEST

The opportunity of the test has been taken to get some information on other subjects related to the second end connection. Therefore this test had a threefold purpose :To perform the second-end connection by drag-inTo check that the trajectory of the pipe on the bottom during towing was consistent with the results obtained by model tests,To monitor the shape of the line by acoustic beacons during the above mentioned operations.

GENERAL DESCRIPTION OF THE TEST

In order to make easier the understanding of the results of the test, we shall first go through the main steps of it, and come back after to peculiar technical points.
Super Short Baseline Hydroacoustic Navigation System
Authors: Vestgaard Karstein , Hansen Kaare
Published: October 2008

Underwater navigation with a super short baseline hydroacoustic navigation system is described.

The description contains design criterium and field experiences.

Offshore activities have a great need for transportable underwater navigation systems with a minimum time for set up and calibration.

Among such activities are tracking of submarines, divers, underwater towed pipes and structures, and as a position reference for dynamic positioned ships and semisubmersibles.

The paper deals with field experiences from operations mentioned above using a hydroacoustic navigation system based on the super short baseline (SSBL) prinsip for position reference.

The system has been used for tracking of pipeline during pull out from onshore base (STAVANGER TO STATFJORD A). Tracking of underwater plough for trenching and for navigating the pipeline into the trench (150 m depth). The system has been used for tracking submersibles during underwater inspection and survey operations. The system is installed onboard a diving support vessel and semi submersible where it is used as a stand alone position reference system.

INTRODUCTION

Hydroacoustic navigation systems are today used as a local positioning reference for ships and submersibles. The systems can also-provide a relative position reference between submersibles and surface ships.

The system can be used by itself as a stand alone navigation system, or it could be integrated with a surface navigation system to give absolute position.

The simplest obtainable hydroacoustic navigation system consists of display and control unit, a transducer unit on the ships hull and a transponder on the sea bed as shown in figure 1.

The system described in this paper is of this type. However, this system could be used in a more complex configuration.

The system is based on the super shortbase line (SSBL) prinsiple with all the acoustic transmit/receive elements housed in one single unit, providing a very simple compact installation. The SSBL system comprises the following main units figure 2.display and control unittransducer containing all the acoustic transmit/receive elementstransponders being the acoustic referende sourcevertical reference unit

The calculated position is based on range and direction measurements to one transponder giving the relative position between the transducer and the transponder. The system can measure relative position to five or more different transponders within the same area.

This is possible because each transponder has its own interrogation and reply frequency.

The system has been employed on project in the NORTH SEA during 1977, where it has been used on several tasks like:position reference for dynamic positioning on diving support vesseltracking operations (bottom tow of pipeline)positioning of a underwater trenching plowtracking of unmanned submersibles