bluuebunny/crossref_metadata_2025 huggingface dataset:
Dredging FeasibiIity of Low Value Iron Sands
Authors: Frazier D.M. , Ayer R.D.
Published: October 2008

This study of mining low value iron ore sands in coastal Quebec indicated that economic viability was marginal considering present market values for iron. The depth and detail of the feasibility investigation, and the small margin of decision emphasizes the importance of the thoroughness of such investigations. The implications were that mining low grade ore by dredge can be competitive if total circumstances are favorable.

INTRODUCTION

Hydraulic dredging for placer minerals is certainly not new. Most operations employ equipment and techniques which are similar to those employed in land fill and harbor construction. However Similar, mining by dredge involves capital costs and risks which are unique to the extraction industries. Construction dredging is characterized by projects of short duration with relatively fixed costs and sales prices. The viability of mining by dredge involves not only the dredging function but beneficiation of the ore, transportation of the mineral to market, processing for the market, and marketing. The life of mining ventures is usually in excess of 20 years; labor and other operating costs normally escalate and the long term market value of the product is to some degree unpredictable.

There is a dearth of reliable published data on marine mining costs. Mining feasibility studies and actual field cost information are either proprietary or obscured with accounting procedures so that little of value can be gleaned by the researcher. The expanding interest in marine mining has generated some hypothetical studies. Unfortunately, these can be no more valid than the assumptions used, and frequently they have no relation to reality. If mining feasibility studies are to have authority each relevant fact must be individually examined and fitted appropriately into the cost picture. Generalities and areas of gross assumption must be eliminated.

PROJECT

Sidbec is a Montreal based steel manufacturing firm which is substantially financed by the Quebec Provincial Government. It had prepared a detailed study on the costs of mining low grade magnetite sands located on near shore and upland areas on the Gulf of St. Lawrence, in Duval Township, Quebec. The investigation was terminated at the end of 1970. The 13% profitiability was less than had been previously estimated, capital costs were higher, and the in depth investigation of the deposit showed that the iron ore reserves were considerably less than had been indicated by previous studies.

It is believed that the costs determined, the depth of the investigation, and the mining and transportation systems evolved are of interest to the marine mining industry. Sidbec has graciously consented to the publication of detailed information developed by their study.
Dredging at Sea
Authors: Donkers J.M. , de Groot R.
Published: October 2008

Dredging at sea can take many forms, determined by the purpose of the dredging job and the sea and weather conditions in the dredging area. The main problems are connected with the movement in waves and swells of the surface vessels supporting the dredging equipment. For a number of sea-dredging operations, satisfactory methods and equipment have been developed; other applications still are waiting for the economical solution. This paper describes some concepts that could lead to the development of both technically and economically feasible equipment.

SCOPE OF PAPER

Dredging can be defined as raising material from the bottom of a water-covered area to the surface and moving it over some horizontal distance. This simple definition covers a very wide range of activities, both with respect to the geographical place and ambient conditions in which a dredging operation can take place and with respect to the goal or purpose of the activity. Dredging jobs can be as simple and straightforward as making or deepening drainage canals in a flat landscape, or as tricky and hazardous as dredging for diamonds in the sea offshore the notorious Southwest African coast. They can range from a 50-cycle/hr operation to a multimillion Yd/annum venture.

It will be clear that no standard solution is available for such widely varying problems. It is safe to say that dredging is one of the most complex technologies of modern man and that dredge design and construction are among the most challenging jobs any engineer could possibly wish for.

The scope of this paper does not permit a comprehensive treatment of all problems that face the dredge designer and dredge operator, when a dredging operation at sea is contemplated. The authors, therefore, limit themselves to a discussion of' the principal applications and types of equipment, the areas where sea dredging is different from inland dredging, and possibilities to design for the additional difficulties.

WHY DREDGING AT SEA?

Let us first consider the reasons why people want to undertake the difficult task of dredging at sea. One good reason f'or dredging is the fact that the sea is not deep enough for our purposes. This is a frequent occurrence in this era of increasing world traffic of many commodities, transported in ships of ever increasing size. To provide access to ports, channels have to be deepened and the increased depth has to be maintained. A typical example of this type of dredging job is the creation of a tanker channel in the North Sea, running over a distance of' 40 miles from the port of Rotterdam and requiring the removal of many millions cuyd of soil.
Bioactive Substances from Marine Sources
Authors: Attaway David
Published: October 2008

The sea is a source of novel organic molecules of importance as bioactive agents in medicine, physiology, pharmacology and biochemistry. Groups of plants and animals which occur primarily or exclusively in marine waters probably contain new and unusual compounds and these groups have received little chemical study. Selected marine hormones, antibiotics, toxins, insecticides and novel organic molecules are reviewed.

INTRODUCTION

This limited review treats of some bioactive substances from marine sources; it is not comprehensive. Many drugs now in use occur naturally or are modeled after natural substances. Gosselin (1) found that almost half of all new prescriptions contained a drug of natural origin. Most of these drugs were discovered in terrestiral organisms (2) and many more are synthetics based on natural terrestrial molecules, such as the following examples in Der Marderosian's comprehensive review of marine pharmaceuticals (3): vasoconstricting drugs based on ephedrine, local anesthetics based on cocaine, and analgesics based on opium derivatives.

Because four-fifths of Earth's animal life lives in or on the water (4) as does a significant portion of the planet's plant life, and because the organic chemistry of few marine organisms has been studied, an unexploited natural resource of organic molecules may await development. There are several phyla and major groups of organisms which occur only or primarily in the marine environment. For example--red and brown algae, zooxanthellae, sponges, echinoderms, molluscs, tunicates, anthozoans, and brachiopods. Included in these groups are kelp, starfish, clams, brittle stars, sea cucumbers, sea squirts, sea whips, and corals. The chemical composition of these groups certainly differ from those of terrestrial organisms, yet less than 1% of marine animals have been examined for biological activity and of these, thousands are known or thought to contain toxic compounds (5). Schwimmer and Schwimmer (6) give hundreds of references to toxic properties of marine and fresh water algae. Toxins, venoms, and poisons are substances which can cause deleterious physiological changes in man and other animals, but when administered in proper dosage, may act as beneficial drugs. Poisonous and venomous marine organisms, therefore, offer logical starting points for finding marine pharmaceuticals and yet less than six have been evaluated to the point of determining their chemical and pharmacological properties (5). Most species of poisonous fishes and a large proportion of other poisonous animals are found in the coral-reef belt. This is perhaps the major reason why Hoffman La-Roche, a Swiss-based drug firm, is establishing a laboratory in Australia for the biochemical study of organisms of the Great Barrier Reef.

The belief that exclusively icthyophagus peoples were free of disease but short lived is reported in F. Adam's translation (7) of The Seven Books of Paulus Aegineta and may indicate the unknowing use of marine drugs in antiquity.
Platform Riser Repair and Protection
Authors: Maciceke Larry V. , Keprta Don F.
Published: October 2008

Risers on offshore structures are exposed to both corrosion and mechanical damage. Atlantic Richfield Company has developed a technique of riser replacement and protection that minimizes the cost of repair and the frequency of corrosion problems.

Replacement of the risers by use of a hydraulic couple for underwater connections worked successfully and considerable savings were realized when compared to the alternate method of flowline pick-up, surface welding and resetting of the line.

The new risers were neoprene coated for corrosion protection. Neoprene has proven to be an excellent splash zone coating. Epoxy was used to coat field joints and repair coatings. The epoxy which cures in air or water is easily applied and effective in corrosion protection.

DESCRIPTION OF PROBLEM

Atlantic Richfield Company operates an oil and gas field (primarily gas) about seven miles off the coast of Texas in the High Island Area. The water depth is approximately 40 feet. Production is gathered from 18 individual caisson well structures and processed through two platform complexes. Submarine flowlines, 3 1/2" diameter 5000 psi working pressure, transfer the (1500-4500 psi) gas and oil from the caisson well completions to the platform production facilities. The flowlines are buried to a depth of 6 feet and protected by sacrificial aluminum anodes. There are 60 risers connecting the flowlines from the wellheads to the platform production manifolds and all the risers were originally welded to the flowlines. In the initial construction of the field facilities, the first 40 risers were coated with an extruded plastic (polypropylene) having a thickness of 35 mils. The other 20 risers were protected by a 250 mil thickness of neoprene. Deterioration of one of the polypropylene coated risers required a replacement of this well's riser and a study into the cause of the problem.

Laboratory analysis of the riser confirmed that the problem was a result of corrosion following the breakdown of the polypropylene coating and not the result of a metallurgical defect. Inspection of the remaining plastic coated risers indicated corrosion and coating damage on several risers. The decision has made to replace these risers to insure there would be no danger to the environment and to minimize the possibility of deferred production. The neoprene coated risers were in excellent condition with only minor corrosion occurring at the field joint above the neoprene.

SPLASH ZONE CORROSION

In tests begun in 1946 at the Francis L. LaQue Corrosion Laboratory of International Nickel at Wrightsville Beach, North Carolina, the greatest rate of metal loss occurs just above the mean high tide (16 mils per year).1 The rate of metal loss is far less in permanently submerged areas and in the atmosphere.
HydroWeld Underwater Welding Process
Authors: Mohr Harvey O. , Kluttz Marvin O. , White Bill E.
Published: October 2008

A new underwater welding process has been under continuous development since 1968. It permits the welder/diver to work in-the-wet while the actual welding is performed in a dry gaseous environment using a specially-developed portable miniature habitat. The actual welding, done by a metal-inert-gas (MIG) process, consistently produces API 1104 Code welds in all welding positions in a large range of steel types and grades. Successful welds have been made to depths of 95 feet possible applications include new construction and repair of virtually any steel subsea structure with surface-quality welding. It is believed that the process will be adaptable to aluminum and any other weldable material.

INTRODUCTION

Early Welding Developments

Welding underwater has been done with varying degrees of success from the beginning of the arc welding process. The achievement of quality underwater welds has always been hampered by the quenching effect of the water on the heat-affected zone and the deposited weld metal. Prior commercial attempts, as well as those used by the various navies of the world,1 have attempted to remove this unfavorable quenching effect by using a stick electrode with a special coating that generates a gas bubble around the arc as illustrated in Figure 1.

Additional efforts to achieve quality welds have been made with the MIG process generating a large free bubble around the arc for the same purpose. All such attempts with both processes have, until recently, produced a marginal weld which rarely approached acceptable standards.

This is attributed to such factors as the size of the bubble which, being too small, allowed a rapid quench. With increasing water depths, the size of the bubble is compressed further, with still more unfavorable results. In unfavorable welding positions, the free bubble becomes even more difficult to control.

These and similar factors lead to welds with an uneven deposit of weld metal containing entrapped gas and/or slag material. The quenched metal in the heat-affected zone becomes too brittle resulting in an inferior weld.

Recent Welding Developments

Stick Electrode

A recent process which was the subject of a previous paper2 has been commercially introduced in this country and used in some locations overseas. This process is thought to use a stick electrode with a special coating to give a larger, more controllable, free bubble. A similar process currently under development in England has been used on at least one commercial job. Although little has been published about the technical aspects of this process, it is believed to represent the best efforts with an optimum coating on the rod combined with rigorous and continuous training of the welder/diver to an acceptable weld under many conditions. It is known that special must be used with each different type of metal. Further, inferior results have been reported when welding high carbon, high strength steels.
Deep Diving From a Dynamically Positioned Drill Ship
Authors: LePage Alain , Wide Peter
Published: October 2008

When offshore drilling started, water was very shallow, but new oil fields were exploited and drilling depths rose rapidly. In shallow water, fixed platforms or jack-up barges were utilized, but when deeper drilling was necessary, drill ships with conventional anchoring were used. Conventional anchoring is possible down to about 300 m, but is not practical deeper than about 200 m. Therefore, about 1970, when the need for even deeper drilling became obvious, the system of dynamic positioning was studied and adapted with its almost unlimited depth capacity.

Diving equipment aboard drill platforms and vessels shows a similar rapid development to meet the needs for greater depths. On the first fixed platforms, only surface diving was carried out and no advanced diving equipment used. As this equipment is heavy, it had to be installed permanently on board to permit quick response of diving services when require a. Normally, the positioning of the diving bell was done by means of a guideline.

The use of dynamic positioning of the drill ships also raises the demands on diving systems on board. Such problems as increasing diving depths are, to a great extent, already solved or on the edge of being solved from the physiological point of view.

The 1972, 2,00l-ft dive at the Hyperbaric facility of COMEX, Marseille shows the human capacity. From the technical point of view, however, the dynamic positioning leads to problems until now unknown in the use of deep diving systems such as guiding and positioning the bell between the surface and the work site, handling without guide lines, supply of gas and power, safety aspects, etc.

Principally and practically, these problems have been solved and the first diving systems are already working from dynamically positioned drill ships, such as the Pelican, from which in Dec., 1972, about 50 dives had been carried out.

THE TYPE OF DIVING TO BE PERFORMED

For different water depths and work, various methods of diving have to be used and the diving systems must be able to meet the requirements as follows:Shallow water surface-to-surface diving from a to 50 m requires no advanced diving equipment.Bounce diving from 50 to 150 m, requires a diving system with decompression capacity of about 15 hours per dive and a diving bell. It is used for short duration work. The divers are compressed rapidly on every dive and are working 1 to 2 hours on the work site. After that, they are decompressed. Mixed gas is used.
Navigation Data Reduction Enhances Plot Accuracies
Authors: Kronberger Fritz P. , Keahey Ned F.
Published: October 2008

Data reduction of navigation parameters recorded in real-time is a key phase of satellite navigation in marine geophysical operations. The positioning system operates in a statistical predictor-corrector manner and is complemented by post processing of the shipboard data to provide the most precise postplots.

INTRODUCTION

Integrated satellite navigation systems are a valuable tool in today's marine exploration efforts. Such systems have proven accuracy and reliability in real-time. However, because of larger statistical data sets, that is, data before and after any given position, the post survey data reduction can further enhance the overall accuracy. Data reduction compensates 'for systematic errors and smoothes the "saw tooth effect" (see Figure 1) of real-time statistical filtering (i.e., Kalman, minimum variance, least squares, etc.).

To perform the reduction task the following steps (see Figure 2) are required:Edit field dataAnalyze and recompute satellite fixesDetermine and remove systematic errorsAdjust random errorsCompute and plot auxiliary dataPlot preliminary mapsCheck and adjust mistiesPlot final maps

BASIC PHILOSOPHY

The basic function of the integrated satellite navigation system is to control the position of the vessel on a preplanned course or "line" during the geophysical survey (see Figure 3). Most operations are defined as "on-line" or "off-line." While "on-line" the integrated navigation system serves as a shot point counter, i.e., it determines the "on-line" course and transmits a discrete pulse, on the basis of distance traveled, to the geophysical recording system which performs the data acquisition and recording operations.

The integrated system, while computing position and maintaining vessel course, records positional information on digital magnetic tape. Computations are based on inputs to a digital computer froma satellite receiver,a Doppler sonar,a gyrocompass,an inelinometer, anda velocimeter (see Figure 4).

These inputs are sampled continuously to determine the vessel's position at one-half second intervals. Onboard data is filtered in a predictor-corrector (Kalman) manner to obtain optimum real-time results. It is this data recorded on magnetic tape and its post processing that is the subject of the discussion below.

SATELLITE FIX COMPUTATION

To compute optimum post survey positions, all navigation data, that is, satellite message data and other sensor information are recorded on magnetic tape. The first step is to edit the field reel verifying all recorded data and checking for data "drop out" (missing data, gaps in recording, loss due to parity errors) and to merge auxiliary data from external navigation aids.

The most reliable data obtained by integrated satellite navigation systems are satellite fixes. Although fixes are not absolutely correct, in a stationary position accuracies of 150 feet RMS may be expected (see Table 1).
Computer Analysis of Oblique Acoustic Reflection For Ocean Sediment Identification
Authors: Newman Anthony K.
Published: October 2008

Remote sensing of ocean sediments via acoustic sounding is usually attempted via simple signal processing of normal-incidence acoustic reflection from ocean sediments. Computer analysis of the acoustic-field-theoretic Green's function for a spherically spreading sound wave from a ball transducer over a semi-infinite visco elastic Voigt model of the ocean sediment has obtained a substantial improvement in the technology of remote acoustic sediment identification.

The Green's function integral, containing the complete description of the acoustic return signal as a function of all the water and sediment parameters involved, is too complex to be integrated in closed-form.

Therefore, IBM 360-50 digital computer subroutines were prepared in Fortran IV (G-level) to compute the value of the integral as various parameters were varied, to obtain the information and insight needed for the optimum system design for remote acoustic sensing of the ocean sediments.

The preliminary investigations of the many possibilities made available by this approach have been quite inspiring. For example at 5000 HZ, the ratio of the 0° (normal incidence) acoustic reflections from coarse sand over those from fine sand (Hamilton's data (1).) is 1.085 : 1. At a geometric equivalent angle of incidence of 60° this ratio is improved to 1.328 : 1. Further improvements are possible if the system is designed to allow multi-frequency and multi-angle operation using advanced signal processing.

Unforseen capabilities have surfaced from computer-experiments designed to test the limits of such improvements. Two different sediments having identical acoustic impedances, (acoustic impedance = Density × Compressional Wave Velocity) with one sediment having 1.1 greater wave velocity and 1/1.1 less density, have identical acoustical return energy at 0° or normal incidence; were computed to have acoustic returns in a nearly 2 : 1 ratio at a geometric equivalent angle of incidence of 60° at 5000 Hz.

Further computer analysis is presented showing increased improvement in remote differential sediment identification via improved system design. The range of possibilities is illustrated by an appendix of computer drawn graphs.

Introduction

The literature contains many accounts of efforts to use the acoustic return from the ocean floor to determine soil classifications and engineering properties of the ocean sediments. Examination of this literature reveals that most investigators have employed the return signals at normal incidence (0°). [See Figure I.] The geometric angle of incidence will be shortened to angle of incidence hereafter. In reference to Figure I it should be mentioned that there are in reality an infinite number of different paths from the transmitter to the receiver, as well as the direct path and path 2 shown, and the net received signal is the superposition of all of them. The angle of incidence merely refers to the angular placement of the transducers.
A New Shear Wave Velocity Measurement Technique in Ocean Bottom Soil Samples
Authors: Celikkol Barbaros , Vogel P.M.
Published: October 2008

The shear wave velocity together with the longitudinal wave velocity and the density of the soil completely describe the first order dynamic elastic properties of the soil. This paper deals with an improved and convenient method of obtaining the shear wave velocity by using inexpensive, portable, and durable equipment. Necessary theory for proper interpretation of data (the experimental technique and data obtained using the system are presented.

INTRODUCTION

The recovery of the essential engineering data necessary for the efficient utilization of the sea floor is tedious and expensive. A low cost, effective, surface-borne acoustic soil assessment system is attractive concept; however, it is not yet fully developed. Preliminary site information that is often necessary for underwater engineering projects is usually obtained by physical tests performed on sediment core samples. Recently, the value of acoustic testing of soil samples has been recognized. Acoustic tests on core samples or reconstituted ocean soils serve two basic purposes. First of all, they provide the dynamical soil constants thus making tedious laboratory measurements unnecessary. Secondly, they provide compressional and shear wave velocity and attenuation information which in turn is necessary data for remote acoustic surveys. Also, any dynamical modeling of soils requires sound velocity and attenuation information.

Historically the most common acoustic measurement on soils has been the determination of longitudinal sound velocity. The longitudinal wave speed through soil samples is relatively easy to obtain and a great deal of information is available in the literature. Determinations of longitudinal sound speed have been made in situ (1, 2, 3, 4) as well as on laboratory sedimented (5), laboratory disturbed (6) and on cored (7) marine soils samples. However, comparatively little information is available on the transverse wave speed, although this parameter is just as important as the longitudinal wave speed. In situ measurements of the Stonely wave velocity (from which the shear wave velocity can be computed) have been made for the top layers of marine soil by Davis (8), Bucher, et al (9) and Hamilton et al (10). The dynamic rigidity of artificially sedimented clays has been determined in the laboratory by using a torsional-oscillator-resonance technique by Hutchins (11), Cohen (12) and Hardin (13) and Humphries (14). Also, a two-hole method has been used to obtain transverse wavespeed in marine (15) and terrestial soils (16).

The purpose of this paper is to describe the theory and the operation of a system that is capable of directly measuring shear wave velocity and attenuation. Here, a shear wave velocimeter for laboratory use is described which is low in cost, portable (hand held) and easy and fast to use.
Sea-Floor Electrical Resistivity Measurement Using a Diver-Operated System
Authors: Corwin R.F.
Published: October 2008

INTRODUCTION AND PREVIOUS WORK

The electrical resistivity of a geologic material is related to the porosity of the material,1 with low resistivity implying high porosity. Resistivity (p) is numerically equal to the electrical resistance between opposite faces of a cube of the material of unit dimensions and usually is measured in ohm centimeters (ohm-cm) or ohm-meters (ohm-m). 8 As porosity is related to sediment composition and engineering properties, in-situ measurement of the vertical variation of the electrical resistivity of marine sediments can provide information about sea-floor structure and composition.

Resistivity techniques are well established on land, and increasing use is being made of them in the off shore environment. Several investigators3–5,7,9 'r, have measured the resistivity and porosity of sea-floor sediments and their results indicate that, except for some highly conductive clays, the formation factor of a marine sediment predicts the porosity of the sediment to within 5 or 10 percent. (Formation factor, F, is defined by the equation,(Mathematical equation available in full paper)

Measurement of the vertical resistivity distribution of the sea floor, therefore, provides a method of determining subbottom porosity and, thus, geologic and engineering properties.

Resistivity is measured on land by borehole logging or by the use of an expanding horizontal surface array. In boreholes, a small probe lowered into the hole provides a continuous record of the resistivity of the material surrounding the probe. 15 This method has been adapted successfully to marine use by forcing a thin probe into the sea-floor sediments, as shown schematically in Fig. 2. The use of a logging probe in marine sediments gives a relatively precise determination of resistivity as a function of depth, but does offer some drawbacks. The depth of measurement is limited to the depth to which the probe can be inserted into the sea floor, which may be small where sediment porosity is low. The volume of bottom material sampled is relatively small for a single insertion of the probe, so interpretation errors may result if the sampled point is not representative of the surrounding area.

Surface-deployed horizontal arrays also are used to measure vertical resistivity profiles on land. S,13 As shown in Fig. 3, this method employs two current electrodes to feed low-frequency, commutated direct current into the ground, and two (or more) potential electrodes to measure the potential difference generated at the surface of the earth by the impressed current flow". The potential difference is a function of the electrode configuration and spacing, and of the subsurface resistivity distribution.

For the equispaced Wenner array shown in Fig. 3, the "apparent, resistivity", Pa, of the earth is given by the formula:(Mathematical equation available in fullpaper)

By expanding the array, the current is forced to flow more deeply into the earth, and the apparent resistivity at larger electrode spacings is indicative of the material-at greater depth.
Sea Bed Geology from Sparker Profiles,Vermilion Block 321, offshore louisiana
Authors: King V.L.
Published: October 2008

A diverse pattern of sands, silts and clays occurs below a thin mantle of young seabottom muds at Vermilion Block 321. The shallow layers are clearly recorded on a network of high resolution sparker lines that traverse the 2,500-acre tract in north-south and east-west directions. These lines provide data for possible platform sites and help document a wide variety of geologic features in the near surface interval. The area, located 90 miles offshore in 200 ft of water, lies within the present-day middle continental shelf province. A series of worldwide Pleistocene glaciation and deglaciation episodes directly influenced sedimentation patterns within the study area. Analysis of the sparker profiles suggests the sediments were deposited at or near an ancient shoreline during a period of sea level lowering. The strata represent a typical deltaic rock sequence. Of particular interest is a southward-oriented distributary channel recorded in both strike and dip profiles. A small, circular salt dome causing noticeable sea-bottom relief over a ½-mile circular area also is shown on the profiles.

INTRODUCTION

A diverse pattern of sands, silts and clays occurs below a mantle of young sea-bottom muds at Vermilion Block 321. The shallow layers are clearly recorded on a network of high resolution sparker lines that traverse the lease in north-south and east-west directions. This paper reviews the near surface geology of the area to a depth of about 200 ft based on an analysis of these sparker profiles. The study has three objectives: to document a variety of geologic features in the near surface interval; to demonstrate the usefulness of sparker surveys in geologic studies; and to provide supporting data for possible platform installation sites.

Vermilion Block 321 is a 2,500-acre block located about 90 miles offshore in 200 ft of water (Fig. 1). Shell acquired the lease at the Dec., 1970, general lease sale. Following acquisition, a dense grid of sparker lines (Fig. 2) was recorded to insure proper selection of sites for delineation wells and platforms. Layers to a depth of about 200 ft can be identified on the sparker records, but bottom multiples hide most events below that level.

The study area lies within the present-day middle continental shelf, an area that experienced a series of depositional cycles controlled by worldwide Pleistocene glaciation and deglaciation episodes. Several cold and warm cycles caused wide fluctuations in sea levels (Fig. 3). At low stands, deltas of the Mississippi and other rivers progressed southward across the shelf and deposited large amounts of clastics far out from the present shoreline (Bernard, 1970). The near surface sediments described in this report were deposited during the sea level lowering that created this old shoreline.
Design of a Controlled Depth, Submerged Barge and Tug System for Arctic Marine Transportation
Authors: Lewis Jack W.
Published: October 2008

This paper describes the feasibility design of an Arctic marine, crude oil transportation system. The system consists of a depth controlled, submerged barge towed by a powerful, surface icebreaking tug. The design of the tug, barge, towing system, and control systems are described.

Because the cargo is carried below the ice water surface, the system is capable of achieving advance speeds through a given ice field which are greater than an equivalently powered conventional surface system. This feature when combined with total system costs, can give the system an economically competitive edge over alternative marine systems.

The paper concludes that the system is technically feasible and that with a suitable development program, an operational system could be realized with present day technology.

INTRODUCTION

The Continental oil Company recently completed a feasibility study of a new marine system in for transporting crude oil from the North Slope of Alaska to the United States' east coast. The system consists of a high powered, surface ice- breaking tug towing, through a flexible cable, a depth controlled submerged barge. The system, it is believed, combines the advantages of both surface and submarine tankers while at the same time eliminating their disadvantages. The barge carries all the cargo and hence avoids the ice and the corresponding large icebreaking resistances. In addition, the barge is not manned and contains only a small amount of power for driving depth control, braking, and low speed maneuvering systems. As a consequence, the barge is, re1atively cheap to manufacture. All of the prime propelling power for the system comes from the icebreaking tug. This component of the system, no longer burdened with the cargo, is made just big enough to house the required propulsion machines Since icebreaking resistance is primarily influenced by a ship's beam, it is kept as small as possible consistent with stability and machinery space requirements.

While this concept appeared very attractive, many questions arose concerning its technical feasibility. Furthermore, even if technical feasibility could be assured, there remained the question of economic feasibility. In an overview paper presented at the TRANSPO Conference in Washington, D.C. in 1972, Sudbury [1] addressed in detail the economics of a total transportation system which used the icebreaker towed submersible barge as the basic transportation unit, but treated only lightly the technical feasibility of the system. It is the purpose of this paper to present a more detailed analysis of the technical aspects of the concept. The design and predicted performance of the icebreaker, barge, towing system and control systems are the main topics such items as ice conditions along the route, terminal design, etc. were very important in the overall study but they will not be discussed in this paper.
Ice Scour on the Northern Continental Shelf of Alaska
Authors: Brooks Larry D.
Published: October 2008

PREFACE

The intent of this investigation was two folds first, to provide an operational, research platform in the Arctic for first class cadets (seniors) of the U. S. Coast Guard Academy to supplement their education in the engineering and ocean science fields, and second, to insure that the research be pertinent to the role of the USCG in the Arctic. As Radm. R. A. Richmond, USCG, stated, "Our role has been and will continue to be to help with the research and analysis required to develop a sensible (transportation) system, and to make recommendations for sensible regulatory policies.

Within these criteria the Coast Guard Academy has been involved in the Arctic every summer since 1969 in the following areas:West Greenland glacier survey,air cushion vehicle evaluation,oil spill effects on ice,ice thickness by shear wave techniques,ice scour on the northern continental shelf of Alaska andicebreaker instrumentation and ramming tests.

BACKGROUND

Ice islands became on interest in 1946 when three were sighted in the Arctic Basin. They were tracked by aerial observations until March, 1952, when the USAF landed a scientific party on one of the three, designated T-3. 2 Several investigators began efforts to determine the origin of these ice islands, and by 1960, it was pretty much accepted that they were calved from the Ellesmere Island ice shelf'. (With evidence that the Ellesmere Island ice shelf is waning in production, there is speculation that many of the Arctic ice islands are from Siberian ice shelves as yet unknown to Free World scientists.) Caught up in the Arctic Gyre, the ice islands drift southwest along the Canadian Archipelago and into the Beaufort Sea.

The USN sponsored three oceanographic investigations into the Chukchi and Beaufort Seas and from these Carsola, in 1954, described a complicated system of bottom micro relief between depths of 30 and 200 fathoms. In water of less than 15 fathoms micro relief was noted on fathometer traces, but of a scale smaller than that in the deeper water. Without reaching any conclusions, Carsola offered five hypotheses as to the origin:glacial deposits,grounding of sea ice and icebergs,sea ice melt deposits,surface permafrost features andmass movement.

In 1968, a large ice island grounded and broke up of Prudhoe Bay and scattered remnants over a distance of 100 miles along the 15 fathom curve. Most of these remnants were about 120 ft thick and had an average horizontal area of about 1 acre. Investigators found the underwater profile of one of these remnants to be undercut in places and protruding in others. Side slopes were generally less than 45°off the vertical.
A Study on the Force of Tidal Current Acting on a Multi-Tubular-Column Structure
Authors: Arita Yukio , Fujita Hideo , Tagaya Kozo
Published: October 2008

The various offshore structures for wildcatting or producing oil are often moored, sit on bottom or fixed on the sea bed, as required by the type of work, in waters where they are subjected to a violent tidal current.

Also, among the contruction projects of long spanned bridges in various countries to meet the demand of the recent development of traffic net work, there are cases where the bridge must be spanned across a rapid strait. In such cases, it is often inevitable to build the bridge piers amid the rapid tidal current of the strait, taking account of the present technology and the economy.

From the point of view of performing the design, production and installation, it has been found most advantages for the offshore structure or the structure of such a long spanned bridge to employ a multi-tubular column type structure.

For designing and building the multi-tubular column structure, the extent of an external force to act on the structure must be assumed. There are many external forces such as wind force wave force, seismic force, current force and so on. In this paper the current force, which comes into question on the occasion of the installation, will be discussed.

The force of tidal current acting on a single tubular column has been studied and reported several times in the past, but no studies have ever been made on the interference in the multi-tubular-column structure. Even if there would be any one, it should have been a small model experiment in a tank and that studying the interference only between two tubular columns.

In this study, a probable 6-tubularcolumn structure was used, and the force of tidal current acting on each column was obtained.

The experiment consisted of a small model test in a tank and a large model test in waters in the Hiroshima Bay. The force of tidal current to act on an actual tubular column structure has been able to be obtained by means of these tests.

The results of this experiment may be used as calculation standards in designing and constructing an actual structure.

Model Tests

I. Models used

Large Model Fig. 1 shows the outline of the large model. The six tubular columns are built into a jacket frame. The pipe columns have smooth surface without painting. Small Model The small model is shown in Fig. 2. The model is scaled down to 1/20 in horizontal section and to 1/10 in vertical section of the large model, respectively. It is made of plastic having smooth surface.
Behavior of Tubular Gusset-Plate Joints
Authors: Bouwkamp J.G.
Published: October 2008

The paper evaluates the stress distribution of in-plane gusset plate joints under both static and cyclic fatigue-load conditions. The potential danger of the in-plane stiffness of the gusset plate in restraining the Poisson effect in the web member sections is illustrated. Under fatigue loading, tapered gusset plate joints in which diametrically opposite regions of the web member section are restrained fail at a lower number of load cycles than non-tapered gusset plate joints. Fatigue failure has been defined as the number of alternating load cycles at which a fatigue crack propagates through the thickness of the web member wall.

It is proposed to omit a penetration of the web member walls and to use either interior or exterior gusset plates. The improvement of both the stress condition and inherent fatigue life through thick-walled web-member sections near the end of the gusset plate is emphasized. The restraint of diametrically opposite regions of the same web member should be prevented.

INTRODUCTION

The rational design of welded truss joints built from circular tubes has been complicated by the radial flexibility of the chord wall or the restraining action of stiffening elements. Both effects cause severe stress concentrations. Under increasing static loads certain joints may nevertheless perform satisfactory because of a redistribution of the load transfer after initial yielding occurs. However, in connections subjected to repeatedly fluctuating loads serious stress concentrations invariably cause a premature fatigue failure. In order to improve the life expectancy of these joints, the designer should aim at reducing these stress concentrations. Although modern finite-element computer programs are presently available to assess the design, a basic understanding of the structural behavior of the joint as influenced by the flexibility and restraining effects of the several components is a primary requirement.

To reduce stress concentrations thicker walled or ring-stiffened column members, or inter welded branch members have been introduced. Also, gusset plates in the plane of the truss have been incorporated. The latter solution permits a substantial portion of the web member loads to be transferred through the gusset plate and reduces the force transfer through the potentially critical chord member wall. The structural danger in that case is no longer related to the radial flexibility of the chord member, but instead, to the concentrated force flow between the branch-member wall and gusset plate, and the excessive in-plane rigidity of the gusset. This latter effect causes a radial restraint of the branch-member walls and introduces secondary stress concentrations in the walls near the edge of the penetrating gusset plate. While the above direct force transfer and resulting primary stress concentrations are inherent with gusset-plate joints, the secondary stress concentrations can effectively be reduced by design modifications which reduce the in-plane stiffness of the gusset plates.
Finite Element Analysis of Complex Joints
Authors: Greimann L.F. , DeHart R.C. , Blackstone W.R. , Stewart B.F. , Scales R.E.
Published: October 2008

This paper explores the application of computerized finite element modeling techniques to the design of complex joints such as those used in semisubmersible drilling platforms. The structural complexity of such joints results in complex stress fields and a lack of suitable analytical methods has caused designers to rely heavily on intuition and simple "cook book" formulas. The advent of the computerized finite element technique fills the analytical void, but experience has shown that practical economic considerations apply certain limits here also. The joint analyst seldom has the time or money available to subdivide his finite element mesh until he has achieved convergence to the "exact solution. The purpose of this study was to develop guidelines for finite element mesh layouts which would yield stress field information adequate for the joint designer's needs.

Five typical joint designs were modeled by finite elements j three by manually laying out the mesh and two via an automatic mesh generation program recently developed at Southwest Research Institute. These finite element idealizations were analyzed using the computer program STARDYNE. The results are compared with experimental stress analyses of scale models performed at Southwest Research Institute. For the cases studied, it is concluded that the finite element method gives results which are within about 20 percent of the experimental results if the elements near cylinder intersections have an arc angle of about 15 degrees along the intersection line and a length of square root rt/2 normal to the intersection line.

INTRODUCTION

The design of the complex joints of offshore drilling rigs is a problem frequently encountered for which no simple solution is available. For example, in the case of large semisubmersible and fixed platforms in deep water, the joints are frequently stiffened with rings, gussets, bulkheads, and insert plates. This constitutes a relatively complex structure so that powerful analytical techniques must be used to produce an adequate design.

Selective reinforcement of a joint at critical regions is the objective of a typical joint design. Intuition and "cook book" methods play an important role in this process. However, too much reliance on these methods may prove dangerous. In general, most designers are well aware that, without detailed knowledge of the stress distribution in a complex joint, one may tend to stiffen an apparently weak area with a resulting increase in stresses in other areas of the joint.

Until recently the only effective means of determining stresses in a complex joint has been to place strain gages on scale models of a proposed structure and locate problem areas by a "cut-and-try" technique, an expensive procedure at best. In the last few years, however, the finite element method, coupled with the digital computer, has provided the structural analyst with a powerful and cost-effective tool to analyze these joints.