bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Structural Design of Tubular Joints
Authors: Visser W.
Published: October 2008

Stresses in thin-walled tubular joints can be calculated with finite-element computer programs that employ 'thin-shell' elements. Such a program, designated SATE, has been developed specifically with the object of determining stress distributions in complex tubular joints as generally encountered in the offshore industry. The program has been applied t()_ several joint geometries and good agreement has been observed between experimental and calculated results. The program thus provides insight into the structural design of tubular joints.

Using the SATE program, the influence of changes in design of both unstuffy and stiffened tubular joints on the stress-concentration factor has been studied. In this context the current API recommendations for simple tubular joint design are discussed. Calculations have demonstrated that in the design of large tubular joints allowance should be made for membrane action rather than for bending of the chord and brace walls. Such an approach leads to joints of low stress concentration.

1. INTRODUCTION

The stress analysis problem of tubular joints in offshore structures has been studied extensively, both experimentally and analytically over the past ten- yearsl. Owing to the complexity of this problem it is still far from being solved. The stress concentration of a joint is a measure of its strength in particular its fatigue strength. Here, the application of the finite-element (f. e.) method for calculating the stress concentration in such linear elastic, thin-walled structures is becoming more and more common practice. Under the assumptions of the thin-shell theory2, the f. e. method indeed suits the purpose of tackling, at least in principle, the wide range of problems related to the connections between flat plates, cylinders and other structural components.

The SATE (§structural Analysis using Ihin-shel finite Elements) program has been developed specifically for determining stresses in complex tubular joints as generally encountered in the offshore industry. The program employs an element as described in ref. 3 following ideas of Herrmann4. In comparison with the Clough-element5, the incorporation of this element in a program is more complicated, but with the same number of unknowns more accurate stresses can be calculated. In the development of the SATE-program a considerable effort has been spent on making the program flexible and economical for both unsatisfied and stiffened tubular joints. The cost involved in solving a tubular joint problem are made up of the combination of input preparation and running of the computer. It would seem that high flexibility and minimum of input preparation are conflicting criteria, as long as the problem of writing a most efficient, general-purpose mesh generator has not been solved. Grete?s progratn6 is a first step in this direction. Some aspects of the SATE program are dealt with in section 2.
Applications of an Offset Floating Breakwater Configuration
Authors: Dailey James E. , Moore Walter L. , Sethness E. Douglas
Published: October 2008

Laboratory tests performed at The University_ of Texas at Austin have shown that a floating offset breakwater configuration can achieve wave transmission coefficients less than 0.2 in both regular and wind waves. The offset configuration consists of vertical reflecting surfaces separated by a distance which is one-half the wave length of incident design waves.

Experiments indicate that the offset break- water provides effective wave attenuation for angles of incidence up to 45 degrees. Therefore, many applications to wave-protection in confused seas are possible. Portability of the floating breakwater permits field adjustment to give the best results. Temporary protection can be provided to construction sites where offshore facilities may be fabricated or installed. Also, the offset configuration can be built into booms for oil slick collection and confinement in heavy seas.

Good motion characterize-tics of the offset configuration encourage many applications to floating structures. A model circular structure for possible use as an offshore supertanker terminal has been tested in the laboratory. An offset configuration is suggested for pipeline lay barges to reduce their down time in rough weather, particularly beam seas.

Introduction

Protection of coastal areas from wave action is commonly achieved by building massive rubble mound structures which are supported by the soil on the bottom. Properly designed, these structures can be effective and permanent, with relatively little maintenance expense. In deep water, however, the first cost becomes very high, inasmuch as the volume of material required increases roughly as the square of water depth.

To provide more economical wave protection in deep water areas, recent interest has focused on floating structures which could be fabricated at inshore locations and towed to the application site. Cost savings result from reduced material requirements and cons traction economies in sheltered areas. Floating structures also have the advantage of portability; they can be moved from one location to another as the need arises. Their main disadvantage is that sizeable mooring forces are often required to hold them in place. These forces may exceed the working capacity of mooring lines or the holding power of anchors, possibly causing a failure in the mooring system. Such a failure could result in heavy damage to or abstraction of the structure.

The offset configuration has been designed with the objective of reducing anchoring force a which are required to hold the floating breakwater in place. Reducing the anchoring forces also implies less structural motion and less wave transmission by wave regeneration. The offset breakwater design has been tested in both regular and wind waves, and it has an even effective in attenuating the heights of both types of waves. Laboratory tests are being continued to obtain experimental misstatements of anchoring force
The Replacement of a Major Brace on MGS Platform A,Submerged Structural COOK Inlet, Alaska
Authors: Hull T.L.
Published: October 2008

This paper describes the replacement of an underwater brace which had been torn from MGS Platform A in Cook Inlet, Alaska. The damage apparently occurred during abnormal winter ice conditions and was detected during a subsequent underwater inspection of the platform. The replacement operation, consisting of the underwater placement and structural attachment of a six foot diameter, sixty-five foot long brace between the platform legs, was conducted in an environment where thirty foot tides and twelve fps currents are not unusual. Diver operations are normally possible only during twenty minute slack tide periods that occur every six hours. Diver"activities are further hampered by the lack of visibility resulting from a heavy sediment load in the swift currents and low water temperatures.

A bolted connection, reinforced with grout, was used to attach the replacement brace to the structure. The extensive underwater work included: trimming the remaining stubs of the original brace to expose the undamaged vertical gusset plates, placing the brace and providing a temporary attachment, drilling twenty-four 1-1/2 inch bolt holes in each of the gusset plates, installation of bolts, sealing the gap between the replacement brace and the trimmed stubs of the original brace, placing reinforcing bars across each joint and grouting the connections. Most diver activities could be conducted from inside the replacement brace, independently of the tidal current, by providing access tubes at either end of the replacement brace for diver communication with the surface.

The brace was replaced within one hundred days after the damage was detected at a cost of about $500,000. Installation was completed in three weeks.

INTRODUCTION

Cook Inlet is a tidal estuary on the southern coast of Alaska. Middle Ground Shoal Platform A, owned by the Shell/Arco/Socal group, is the first drilling/production platform installed in Cook Inlet, Alaska. The platform site, Figure 1, is between the East and West Forelands in about ninety feet water depth and is exposed to severe tidal ranges up to about thirty feet. Swift tiday currents, particularly through the constriction caused by the Forelands, are normal and can exceed seven knots.' The current abates only during short slack tide periods which occur about every six hours as the tidal flow reverses. This period of relatively still flow averages about twenty minutes.

During winter months the Inlet is' covered with ice which may exceed several feet in thickness. 2 Ice stamukhi, tens of feet in thickness,3 can be formed as layers of ice are frozen together on the beaches and subsequently broken loose by receding high tides. The ice, driven by the tidal current, applies considerable force to the Inlet platforms and represents the major design load.
New Radioelectric Pi Lot Aid For Harbor Entrance
Authors: Laurent Pierre
Published: October 2008

A new oil terminal is being built at ANTIFER, north of Le Havre. This harbour is intended to accomodate ships up to 300,000 tons. It has been found necessary to equip this harbour with a modern system allowing ships to be guided with a great accuracy, from the entrance of the channel to their berth.

An original guidance system has been developed. It is mainly composed of a radiolocation device, of a position data processing center for the generation of the parameters required for the pilot, and of a light portable equipment allowing a convenient display of these parameters.

The flexibility of the techniques used to answer the particular requirements of the ANTIFER terminal makes possible their adaptation to the numerous cases of harbour entrance areas.

CONNING SYSTEM FOR HARBOUR ENTRANCE CHANNELS

Introduction

The solution of the problem set by the guidance of ships in harbour entrance channels obliges to inform permanently the pilot of the Tnstantaneous value of. Some parameters as well as their sign and their evolution tendency.

It is therefore necessary, during the whole trip of the ship from her approach at the entrance of the channel towards her berthing, or vice versa, to select the necessary data, and to process them in real time so as to determine the parameters. These parameters are then retransmitted to the ship and displayed for use to the pilot in a direct and convenient form.

The system has to be prevented from any risk of error or misfunctioning; it has to be equipped in particular with self-testing devices and tests processes ready to be operated at any time.

Such a system is under way of realization for the French harbour of ANTIFER near Le Havre.

I.ANTIFER HARBOUR

ANTIFER harbour, a new oil terminal located at about 20 kilometres northwards of Le Havre, is mainly intended to harbour ships up to 300,000 tons.

Figure 1 shows the scheme of the portuary facilities, of the access channel with the waiting zone.
Material Properties of Submarine Mississippi Delta Sediments Under Simulated Wave Loadings
Authors: Esrig Melvin I. , Ladd Richard S. , Bea Robert G.
Published: October 2008

Specimens of Mississippi delta sediments were subjected to simulated wave loadings in triaxial testing equipment. About 100 stress cycles of a sinusoidal form were applied under undrained conditions at about 3 cycles per minute.

Decreases in the normalized modulus (modulus Es/undrained shear strength Su) with changes in normalized stress excursion (applied excursion g/stress at failure gf) and number of cycles gf loading are shown and quantified. The applicability and limitations of these data to the analysis of submarine slope stability is discussed and recommendations for future studies are provided.

INTRODUCTION

Submarine landslides, which have severely damaged several offshore structures (1) in portions of the Mississippi delta, are known to have occurred in areas where the average inclination of the underwater ground surface is as flat as 1:125 (about 1/2 degree). The application to this problem of concepts of-soil mechanics that do not consider the interaction of the soil and the fluid above the sliding mass have never been able to provide a convincing explanation for the cause of these landslides. (2) Rational explanations have been provided when the response of the submarine soils to the hydrodynamic pressures produced by storm waves were considered in the analyses.(3) Storm waves apply transient pressures to the sea floor which, at a given point, may be considered as varying approximately sinusoidally in time. The frequencies of the long waves during major storms may reach 3 to 6 cycles per minute and the repeated, cyclic stress, applied by these waves to the sea bottom may continue for several hours. An understanding of the response of submarine soils (i.e., their variations in modulus and strength) as a result of these transient pressures is needed for inclusion in stability and deformation analyses.

Deterioration of soil strength and other physical properties as a result of repeated loading is a phenomenon which is considered routinely in earthquake analyses, vehicle mobility analyses and now in the analysis of submarine landslide potential. Presented in this paper are some of the results of a laboratory study using triaxial testing equipment of the response of Mississippi delta sediments to sinusoidally varying cyclic loadings of 3 cycles per minute. Alterations in soil modulus with increasing cycles of stressing and increases in cumulative strain during testing are reported and are related to alterations in soil strength. The data have been " normalized" to permit generalization and use in finite element and other models.

MATERIALS AND TEST PROCEDURES

The material used in this investigation was recovered in 300 to 400 ft of water as " undisturbed" tube samples from the landslide area in South Pass Block 70. Three zones are identified withinthe soil profile; Zone I is termed the " crust" zone; Zone II the " slide" zone, and Zone III the " deformed" zone.
Analysis of Simulataneous Wave Force and Water Particle Velocity Measurements
Authors: Kim Young Yuel , Hibbard H.C.
Published: October 2008

A constant drag coefficient of 0.61 was calculated over a Reynolds number range of 2×105 to 8×105 from simultaneous measurements of-wave-induced velocities and forces. The average inertia coefficient was 1. 20. The constant drag coefficient found for a Reynolds number as low as 2×105 allows a simulation of design wave force with a smaller scale space frame structure.

The drag (inertia) coefficients were determined from drag (inertia11y) dominant portions of individual wave cycles. The measured wave force power spectrum agrees well with that calculated from measured velocities with average drag and inertia coefficients.

INTRODUCTION

The objective of this study was to establish the feasibility of measuring wave forces on a small-scale structure that could be scaled up to typical design loads on a conventional jacket-type offshore platform. It is essential to show that a supercritical flow condition (typified by constant drag coefficient) occurs over the entire structure to make such scaling possible. It is not possible, however, with existing wave-force data to show at what Reynolds number this supercritica1 condition begins, because the water-particle velocity must be inferred from the surface wave elevation. By measuring both the wave force and the particle velocity, one can remove the uncertainty due to wave theory and possible steady ocean currents affecting the calculated drag coefficient.

When unambiguous data that can be scaled up to typical design loads are obtained from a smaller scale test structure, they can be used to calibrate present-day design wave-force calculations [4]. Currently used design force calculations for a space-frame structure are based on wave-force measurements on a single pile, typically the wave-force data collected by Chevron during Hurricane Carla [2,3,9]. Design waves are assumed to be smooth and long crested (two-dimensional). Actual waves, however, are neither. The spatial distribution of particle velocities calculated for idealized design waves can be different from those for real, random waves. For the same average velocities, the drag forces on structural members are subject to random variation due to turbulence. The net result of these effects can be randomly varying force vectors over the space of a structure. Because of the changing directions of force vectors, not all of the wave forces are additive. The actual structural load in real waves may be different from when the forces are assumed in the same direction over the entire structural space, as in present design wave-force calculations.

Scaling Wave Forces

In order to simulate one physical system with another of different size, the two systems are required to be geometrically similar. In addition to geometrical similarity, certain dimensionless physical parameters must be preserved so that the experimental results of one system can be applied to another. Such parameters can be found by dimensional analysis of the governing equations for the physical system under consideration.
Role of the Nucleus in Formation of Ferromanganese Nodules: Processing Guide lines for the Marine Miner
Authors: Morgan Charles L. , Moore J. Robert
Published: October 2008

Detailed chemical and micro-analyses of ferromanganese deposits from the North Pacific and Blake Plateau reveal several key elemental and textural trends which are of interest to the ocean miner. By using wet chemical separation procedures and spectroscopic elemental analyses, we determine the bulk composition of the different nodule constituents, and on the same samples use the micro-analysis capabilities of the scanning electron microscope and energy dispersive detector to discover how the economically important metals, such as Cu, Ni, and Co are arranged around the nuclei of the same nodules. These experiments use operationally defined distinctions between the authigenic and detrital fractions of the nodules, and then justify these distinctions by comparison of the chemical, mineralogical, and geometric features of the separated fractions. Comments on application to chemical processing of the nodules, chiefly economic aspects, are presented.

Introduction

It has often been said that diversity is the only common denominator among the many ferromanganese oxide deposits of the world, in terms of minor element abundances and growth substrates. In fact, only a very few relationships between the compositions of the deposits and the various substrates (which comprise the nucleating surfaces of growth) have been established. Most investigations of world-wide trends have relied chiefly upon bulk chemical data for comparison of the different deposits, and the role of the nucleating surfaces in determining the composition of the resultant nodules, or crusts, has remained largely unknown. Since ferromanganese oxide deposits of all types are unquestionably surface-related, if not surface- controlled phenomena, we have proposed that a fine-scale examination of these growth surface when combined with a series of bulk chemical analyses on the same samples, would help ascertain which surface-related factors are important in controlling the metal content and extractability in the different deposits. Thus, with support from the National Sea Grant Program we began a series of experiments directed toward determining what effect, within the framework of regional source controls, the nucleus has on the ultimate composition and structure of ferromanganese deposits.

The results of these experiments have provided much useful data in deciding among the various models of nucleation and growth in ferromanganese deposits, and they also reveal several trends which strongly influence the ore grade of the deposits. It is with these latter trends that we are concerned with here, with special emphasis on the respective roles of iron silicates, and carbonates as nuclei and as possible hindrances to easy metal extraction.
Power Testing of Offshore Generating Systems
Authors: Stephen D.D.
Published: October 2008

Introduction

The commissioning of an electrical installation off-shore on a drilling/ production platform presents very different problems to those experienced with equivalent equipment on-shore. Many factors combine to cause this and among the most important are the restricted number of personnel which can be accommodated, the significance of time delay on a project with such high capital investment, the great importance placed on the maximum safety, security, and reliability throughout the complete operation, the concentration and complexity of the many control, monitoring, safety and alarm systems in combination with the many systems of power generation provided, and not least the adverse environmental conditions suffered by the equipment during erection, storage and transportation in modules, and final erection on the platform with considerable exposure to shock, vibration and severe climatic conditions.

To reduce these off-shore problems and ensure minimum off-shore time required to put the electrical system to work it was decided to carry out full-scale on-shore testing programmes on the electrical generation equipment for the first two BP Forties platforms. These involved considerable logistical problems as well as those involved in the purely technical operations but the results obtained from both sets of tests have fully justified the operation.

Testing Programme

The electrical generation equipment and its layout on the platform has been fully described elsewhere, refs. 1, 2 and 3. Packages 1 and VII contain the main gasturbine generator sets, their control and starting equipment, the 11 kV switchgear, power transformers, 3.3 kV switchgear convert or equipment, diesel-generator ' set,415V switchgear and motor control centres, and items such as switchgear batteries, neutral earthing resistors and items necessary to provide a complete generation system. By placing these two packages close to each other, in the case of the Rotterdam unit on the same barge, interconnection was relatively simple.

Although all the separate items of equipment were fully inspected and tested at their place of manufacture many of the control and operation sequences are unique and had not been used previously on such a concentrated and self-contained system. In addition the procedures of packing, transportation, prolonged storage, sometimes under adverse environmental conditions, erection in modules still under fabrication, and intercabling, all combine to introduce a high probability that considerable rechecking would be essential to detect any damage or deficiencies. It was also considered desirable to fully test and prove the coordinated functioning of interconnected systems of power generation, control, protection and instrumentation whose components had never been operated conjointly although this would require considerable expenditure on test equipment and manpower.

The testing programme enabled the following aspects to be proved to a very high degree ofcompletion.
The Sea Ratchet for Semi Heave Reduction
Authors: Haselton F.R.
Published: October 2008

The SEA RATCHET* is a device which will substantially reduce wave induced motions as well as increase deck loading flexibility.

Slung deeply beneath existing semis using chains, the ratchet action results from its upward only damping action entraining a hundred thousand tons of apparent mass. Filmed scale model tests are shown.

INTRODUCTION

All relative motions between drilling platforms and the earth are undesirable with the single exception of forward translation during mobilization. Semis present a logical attempt to reduce heave, pitch and roll motions through the use of large size and mass coupled with small water plane area. The heave motions which remain are reduced even further through the use of drill string heave compensators. There occur, however, periods when the sea state overrides the present capabilities to deal with heave and operations must shut down. Unfortunately, daily costs do not shut down and, in some areas, significant annual down-time losses mount to millions of dollars. What recourses have semi users for reducing these losses? There are three: larger platforms, creating a larger ratio of platform mass to wave energy, active six degree of freedom hydrodynamic controls, as suggested last year in paper 2030; and more effective passive damping. The size of present semis is not likely to increase enough to significantly reduce wave induced motions because of construction limitations as well as costs. Active control systems, while feasible for future design semis, can do nothing for existing platforms or those already planned. A retro-fitable damping system may offer a solution and is the subject of this paper.

DAMPLNG TECHNIQUE TODAY

Nearly all semis embody damping techniques most generally in the form of the flat deck surfaces of the submerged hulls. -Unfortunately, these surfaces are neither large enough nor deep enough to significantly reduce heave, particularly in very heavy weather. Structural as well as stability considerations preclude longer columns and more deeply submerged pontoons. If adequate damping surfaces could be sufficiently removed from the sea surface yet rigidly attached to the semi, their effectiveness would be greatly improved. One such system has been proposed and scale tested as reported in OCEAN INDUSTRY, August 1971, by Jack R. Hilder, Jr., of Special Offshore Services. Its mechanical complexity coupled with the difficulty of retrofitting existing semis probably has hindered its acceptance in the community despite the improved model test results indicated in the article.

A brief review of basic wave theory will reveal- that the vertical component of water wave particle motion decays exponentially with depth such that for every A* increase in depth below the mean water surface the motion is halved. Unfortunately, higher waves are associated with longer wave lengths and longer periods while a semi's heave response generally degrades with longer periods. As any submariner can verify, virtually all vertical surface induced motion ceases below 100 meters, even in the most violent storms.
What Will We See Beneath The Sea?
Authors: Savit Carl H.
Published: October 2008

If present trends in marine geophysical exploration continue, and if the rate of new technology advance is not inhibited by political or other external factors, great advances may be expected in what can be seen beneath the sea?s bottom. The bright spot technique is in its infancy and is evolving lines of advance in the extraction of stratigraphic information from seismic reflection data. The next five years should see the doubling of the resolving power of the seismic method together with a reasonably reliable method for determination of gross lithology. In the fine detailing of individual prospects, methods should be available for fine-tuning lithologic identification.

TEXT

That a question such as the one posed by our title can be a serious subject of a technical meeting is in itself a remarkable sign of the growth of science in this century. To the 19th-century scientist, the depths of the sea were a great mystery. He had a few soundings made with a rope or wire line to tell him tantalizing bits of information about the topography of the sea bottom. But even so prominent and ubiquitous a submarine topographic feature as the sea mount or guyot had to wait until World War II to be discovered. Only within the last three decades have we really been able to hope to map, in any detail, the interfaces beneath the sea bottom.

The seismic refraction method was the first technique used to map submarine layers. As with the old soundings, however, the refraction method brought only isolated, discontinuous bits of information about some submarine layers.

It was not until the seismic (or acoustic) reflection method was introduced into submarine mapping that some continuous map data became available.

Submarine seismic reflection profiling has two distinct and distinctive ancestral lines. One group of marine technologists had developed the technique of mapping the ocean bottom with sound waves--sonar. With time, the sonar transmitters had become increasingly powerful to cope with deeper or more poorly reflecting ocean bottoms. Inevitably, sonar records (fathograms) were found to depict reflecting boundaries beneath the bottom.

From this beginning, it was quite natural to continue to increase the power of the sonar system to achieve ever greater penetration beneath the bottom. All of the successors or descendants of sonar had a common configuration. On or near the survey ship was a transmitter of some sort. Almost anything that could (or might) be used to make an underwater sound was pressed into service. Devices ranged from piezoelectric crystals and magnetostrictive metal rods, through rubber balls inflated to bursting, to spark generators and electro-mechanical implosion devices. To receive the return signal, a single hydrophone or single hydrophone array was mounted on the hull or towed close to the ship.

Penetrations of the sea bottom of up to one or two thousand feet were routinely obtained. When the late, great Maurice Ewing substituted half-pound blocks of TNT for the other sound sources, the results were spectacular.
W1nd and Current Effects on Large-Scale Oil Slicks
Authors: Murray Stephen P.
Published: October 2008

The relative effect of local winds and near-surface currents in determining the movement of oil slicks in coastal and shelf waters was determined from 39 surveys by Raydist equipped helicopters during the Main Pass 41C spill off the Mississippi Delta in March 1970. Orientation of oil slicks is closely controlled by local wind direction; slicks usually form 10°−40° to the right of the wind. Wind shifts associated with various sectors of migrating high-pressure cells quickly realign new slicks and actively dissipate old ones. Density fronts, both ambient and quasi-stationary, also play important roles in determining slick movement and size. An easily utilized regression model for slick area and orientation as a function of wind velocity and local conditions is also presented.

INTRODUCTION

Production platform MP−41C, off the east flank of the Mississippi Delta in 15 m of water (see Fig. 1), caught fire at 3 a.m. on Tuesday, February 10, 1970. While it burned unchecked over the following 4 weeks, small, light slicks formed around the platform as water was pumped onto the flame. On March 10 the fire was extinguished, and large-scale oil slicks began to develop immediately from the estimated 1,000 barrel per day discharge. Significant oil slicks continued over the next 20 days, until all wells were capped. The geometry and movement of these slicks are the subject of this paper.

From March 5 to March 21 the Coastal Studies Institute of Louisiana State University, in cooperation with the U.S. Coast Guard, conducted an intensive field investigation of tides, winds, and currents throughout the area affected by the oil slicks.1 The information on oil slicks and subsequent conclusions about their behavior were deduced from a number of brief aerial reconnaissance flights by Institute personnel and the study of aerial imageries taken intermittently, mainly for test and evaluation purposes, by the U.S. Geological Survey, the National Aeronautics and Space Administration, and a private company, Remote Sensing Inc. The few complete oil slicks present in that data set were found to agree quite well with a turbulent diffusion theory of oil spreading outlined by Murray. 2 That diffusion analysis applied, however, only to the idealized case of an oil slick in a steady, uniform current; no effects of unsteadiness in wind, spatial changes in the current field, or time-dependent tidal currents were considered owing to lack of sufficient data.

Fortunately, the Chevron Oil Company, owner of the MP−41C structure, independently surveyed oil slick geometry on a twice-daily basis.
The Mechanical Efficiency Of A Seismic Energy Source
Authors: Jenkins Peter E.
Published: October 2008

INTRODUCTION

The energy source evaluated in this paper is the pneumatic air gun now being used by Texas Instruments, Inc. of Dallas, Tex. in their marine seismic operations. To the author's knowledge, the only efficiency that has been previously determined on the gun was an acoustical effectiveness, based on an isothermal system. The present analysis will show that the system is, not isothermal and that the efficiency of the gun decreases proportionately to the gun's operating depth.

The principle of operation of the pneumatic source is that a volume of high pressure air (2,000 psia) is suddenly released underwater to form an air bubble. The resulting air bubble oscillates (expands and contracts) until all of its energy is dissipated; part of the energy is radiated acoustically and the rest is dissipated viscously.

In examining the sequence of events in greater detail, an acoustic pulse is emitted when the volume of high pressure air is suddenly released. The amplitude and rise time of this acoustic pulse depend primarily on the air gun chamber pressure (Pc) and volume (Vc) and on the local hydrostatic pressure. A portion of the energy is liberated in this first pulse and the rest resides as potential energy of the bubble to do work on the surrounding water. The bubble then starts to contract due to this pressure deficit, and its inward motion is checked due to the compressibility of the air bubble. Hence, a damped oscillatory system is set up by inertia of the water and elastic properties of the air and water, with damping being provided by viscous effects. The number of oscillations the bubble undergoes, depends on the initial conditions of the bubble (Pc and Vc), the depth at which the gun is fired, and the damping properties of the surrounding water.

EFFICIENCY

The efficiency of the energy source can be described as(Equation available in full paper)To determine each of these energy terms, the following analysis will be made, using the principles from the first law of thermodynamics.(Equation available in full paper)
Two Years Experience With the SBS
Authors: Dangles O. , van Heijst W.J.
Published: October 2008

The first SINGLE BUOY STORAGE (SBS) system was installed in February, 1974 and became operational on March 23rd, 1974. The technical merits of the SBS are described in OTC paper 1918 (May 1973). After 23 month of operation it is concluded that the BBS system has given full satisfaction to the operator, Aquitaine Tunesie, a subsidiary of the Elf/SNPA Group.

This paper describes the experience obtained from the mooring operation, the off-loading, the equipment and the limitation of the operational procedures during the loading of 120 tankers with a total of 26 million barrels.

INTRODUCTION

The SBS storage is a barge of 70,000 DWT called Ifrikia which is permanently moored to an SBM by means of a rigid arm. Tankers of about 35,000 DWT are loaded when moored side by side the SBS.

For the operation of the SBS system a staff of 20 to 25 persons is permanently on board the Ifrikia.

All operations - loading, mooring, maintenance, etc. - are directed by the terminal superintendent, who also acts as barge captain, mooring master and pilot. Assistance can be obtained from a tug permanently on site for emergencies, pollution and fire fighting, etc.

GENERAL INFORMATION, ECONOMICS

The estimated production rate during the discovery period in 1971 was 10 million barrels per year and the production equipment was laid out for a maximum production rate of 17 million barrels per year. This production level has now been achieved.

The field includes:One drilling platform with a possibility of a total of 18 wells including those for water injection.One production platform.One flare platform.One Single Buoy Storage system (SBS).

Apart from the SBS, the system is, completely conventional. Economical and technical calculations showed at the time of development, that a pipeline would be more economical if the total production was about 25 million barrels/ year. These economics will however differ from field to field depending on the site conditions, distance to shore, and the prevailing market costs for the various systems (pipeline versus floating storage etc.).

It is interesting to note that the investment in the SBS and off-loading equipment installed for SNPA is relatively low and is equivalent to $10.50 per barrel of storage. The total cost associated with the ownership and operation of the SBS system amounts to $ .42 per barrel.

DETERMINATION OF STORAGE CAPACITY AND SUBSEQUENT OPERATIONAL CAPABILITY

Initial studies at the project stage indicated that wave heights up to approximately 6 feet were a reasonable basis for berthing, subject to favorable wind and current conditions.

Available weather data predicted that waves in excess of 6 feet with a continuous duration of 96 hours would only occur once every ten years. It was therefore decided to base the storage capacity on 96 hours field production.
Movement Of Sediment On The Gulf Of Mexico Continental Slope And Upper Continental Shelf
Authors: Woodbury H.O. , Spotts J.H. , Akers W.H.
Published: October 2008

Grain-size, coarse-fraction analyses and depositional environment as interpreted from microfauna are related to the character of sparker reflections at the location of core holes drilled by Exxon, Chevron, Gulf, and Mobil on the continental slope of the northern Gulf of Mexico. Continuous sparker reflections are correlated with slowly deposited, evenly bedded sediments containing bathyal faunas. The coarse fraction is dominated by the tests of foraminifera.

Discontinuous, discordant reflections and diffractions are correlated with sediments more rapidly emplaced in the bathyal environment of the continental slope by slumping and sliding from the continental shelf. Their coarse fraction is dominated by terrigenous sand grains. A large portion of the volume of continental slope sediments appears to consist of these "displaced" sediments, including an area 3 to 24. km wide and 80 km long, southeast of Corpus Christi, Tex.

Comparable processes of movement of sediments are interpreted on the continental shelf south of the Southwest Pass of the Mississippi River. Bathymetry in this area is characterized by a series of subaqueous "gullies" radiating from the river mouth leading to terraces at their southern extremities. Side scan sonar and PDR surveys show a rough bottom in these gullies and terraces as contrasted with a relatively smooth bottom elsewhere. The rough bottom is interpreted as indicative of slump and creep of the sediments from shallower water. Some foundation soil borings in this area south of Southwest Pass find a low strength material gradually increasing in strength with depth. Other borings find a "crust" of anomalously strong material B to 15 m below the mud line. The microfauna recovered from the crust has moved to its present position by slump or creep from shallower water along a pattern comparable with the gullies shown in the present-day bathymetry.

INTRODUCTION

This paper discusses and interprets sediments and sedimentation of the continental slope of the northern Gulf of Mexico based upon data from core tests and sparker seismic surveys conducted by Exxon, Standard Oil Co. of California, Gulf, and Mobil in 1966, and relates these data to sediment movement south of the Southwest Pass of the Mississippi River. Sediment penetration of the core holes was restricted by government regulations to 305 m (1,000 ft) in water depths no leas than 200 m (650 ft). The general procedure was to cut a 4.6-m (15-ft) core and then to drill approximately 15 m (50 ft), followed by another 4.6-m core, and so on.

Environment of deposition, as determined by W. H. Akers, from the microfauna and other materials in washed residue; grain-size and coarse-fraction analysis, as interpreted by J. H. Spotts; lithologic descriptions by J. W. Low and N. E. Cygan; color photographs of the cores; bulk density measurements; and mechanical logs have all been used in varying degrees to interpret sedimentation on the continental slope.
Large Dunes and Other Bedforms in Lower Cook Inlet, Alaska
Authors: Bouma Arnold H. , Hampton M.A , Wennekens M.P. , Dygas J.A.
Published: October 2008

The surficial geology of lower Cook Inlet, Alaska, reveals: numerous fields containing bedfroms of various sizes and types, a smooth bottom, sand patches, or boulders. High-velocity tidal currents exceeding 3–4 knots (150–200 cm/s) dominate the hydrodynamic environment. The fields normally are elongate in the axial direction of the inlet, parallel to the dominant tidal flow. Lengths of the fields normally exceed several kilometers; their widths range from a few hundred to a few thousand meters. Although ebb and flood surface currents in lower Cook Inlet are typically about 3.5 to 4 knots, currents of 5 to 6 knots (250–300 cm/s) are not exceptional. In the 25 km-wide constriction between upper and lower Cook Inlet, tidal currents may peak at 9 knots or higher.

The most abundant group of bedforms are sand waves, some as large as sand ridges. Normally, smaller sand waves ride on their flanks, and opposing asymmetry may indicate opposite transport directions for the large and small waves. Dunes are less common and have not been seen covering large fields. Sand ridges, having their crests parallel to the current flow, are about 10 m high and have spacings of 300 to 400 m. Other bedforms observed are sand ribbons and sand patches, and gravel and boulder fields. Shallow parallel grooves, partly filled with small dunes, were observed on sonographs. Seismic studies indicate that these grooves occur where steeply dipping strata reach the surface and are sculpted by differential erosion.

Although nothing is known about the migration of these various bedforms, the oppositely oriented asymmetry of large sand waves and the smaller superimposed ones suggests some degree of transport. Bottom television observations, revealing active motion in the form of small current ripples, support bottom transport. An understanding of these various bedforms and other bottom characteristics and their distribution and movement is essential to future oil and gas development, in particular to the safety of exploration/production platforms and pipelines, and to biological studies, primarily those dealing with benthic organisms.

INTRODUCTION

Lower Cook Inlet is the south part of the large tidal inlet that connects Anchorage with the Pacific Ocean (Fig. 1). Pacific waters, moving in part as the Alaska Current in a counterclockwise motion along the Kenai Peninsula, enter Cook Inlet from the southeast via Kennedy and Stevenson Entrances. The flood current moves predominantly along the eastern shores of Cook Inlet, whereas ebb waters flow mostly south along the western side of the inlet.

High-resolution shallow-penetration seismic subbottom profiling systems -Uniboom and 3.5 kHz were used on board the USGS R/V Sea Sounder in June-July 1976 to obtain environmental geologic information about the surficial geology (Bouma and Hampton, 1976; Hampton and Bouma, 1976). During this survey, large bedforms were found in many areas (Fig. 1). In some of these areas, a side-scan sonar survey and bottom television observations were made.
Wind Tunnel Hydrodynamic Testing Of A Large Submersible Vehicle Model
Authors: Van Ryzin Joseph C.
Published: October 2008

During the development of a large (270 ton) underwater remote-controlled vehicle, it became essential for the control design that tests be conducted to determine the steady state hydrodynamic drag characteristics of the submerged vehicle. Such a large complex shape is difficult, if not impossible, to model with the correct Reynolds number in water because of the huge drag and power requirements. Testing of this vehicle was done in a wind tunnel with almost exact Reynolds number correlation. Air can be used for testing of underwater vehicles as long as the fluid is reasonably incompressible (low speeds), there is no free surface and no cavitation; it is also advantageous if the flow is not critical.

If the model is sized to conveniently fit into the wind tunnel test section, the required air velocity to reach the appropriate Reynolds number is within the approximate incompressible range (approximately 330 ft/sec) and the test forces are within the test facility balance range, then the vehicle can be conveniently tested in a wind tunnel.

This particular vehicle was tested at various roll, yaw and pitch angles to evaluate six-component forces and moments. Reynolds number effects, support tare and vehicle configuration changes were studied. The results of the test provided invaluable information for an accurate evaluation of the vehicle maneuverability and handling characteristics. Larger than expected roll moments and lift forces were encountered and compensating vehicle control design changes were made.

In conclusion, wind tunnels offer an excellent alternative and, in many cases, a better alternative than testing the vehicle in water or relying solely on an analytical solution.

INTRODUCTION

The 270 ton aluminum Submersible Pipeline Repair Vehicle (SPRV) is a twin hulled, variable ballast submersible with 9-foot diameter hulls, 156 feet long, four bridge beams of syntactic foam and aluminum, six 8-foot diameter Kort nozzle thrusters, and various tooling and electronics. This vehicle is being developed for Shell Development Company. A floating model of the vehicle is shown in Figure 1. The purpose of the SPRV is to repair deepwater pipelines. It is remote controlled via an umbilical from the surface.

The SPRV is designed to operate in a 1.5 knot bottom current and, since it docks parallel to the pipeline, it must be able to hover at any orientation (yaw angle) to this current. For proper design of the control, maneuverability, placement of the thrusters and thruster power requirements, the loads caused by the 1.5 knot current had to be known. There are six load components of concern: frontal drag, thwartship drag, lift, yawing moment, pitching moment and rolling moment.