bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Experimental Design in Selecting a Development Plan for the Agbami Field
Authors: Spokes J.J. , Ovuede M.A. , Ginger E.P. , Narahara G.M. , Haga Olav , Gontijo Julio
Published: October 2008

The Agbami project team was challenged to generate a field development plan and to assess that plan over a wide range of uncertainty. Complete stakeholder alignment around the technical aspects of the development plan was a critical issue.

Field data, laboratory data, and analog data were incorporated into a range of reservoir simulation models. The field data included appraisal well logs, cores, 3D seismic, fluid samples, pressure data, and drill stem tests. Three hundred reservoir models were constructed and ranked using streamline simulation for both static and dynamic attributes to assess the range of subsurface uncertainty.

A project team with significant but diverse deepwater development experience was formed and co-located. A formal phased decision making process was implemented. During each phase of the process key parameters of uncertainty were identified and ranked in terms of project impact. Field development options were evaluated in distinct phases over the full range of uncertainty.

Experimental Design (ED) methodology was used throughout the evaluation to obtain the maximum information with the minimum computational effort. The paper shows how the results from this process facilitated the identification of the key uncertainties and provided direct input into economic models for decision analysis.

In Phase Two of the evaluation the pressure maintenance scheme selected for the 17 million year (MY) reservoir was crestal gas re-injection with peripheral water injection. Crestal gas re-injection was selected for the 14MY and 16MY reservoirs. The facility capacity requirements were also selected during this phase at 250,000 stock tank bbl of oil per day (STB/D) and 450,000 thousand standard cubic ft per day (Mscf/D). Peer reviews and assists were held and alignment was obtained along with action items to be included in the subsequent phase.

In Phase Three of the evaluation the well count parameter was investigated and an optimum number of 38 wells was selected. Production profiles were generated and presented in terms of P10, P50, and P90.

Introduction

This paper will focus on the application of Experimental Design (ED) during Phase Three at Agbami. With drilling depths of up to 10,000 ft below mudline in 4,800 ft of water, well costs at Agbami are at the high end of typical deepwater costs. Therefore, the number of wells including their type and location is an important optimization parameter in the field development plan. The probabilistic forecast of all produced and injected fluids is also a key deliverable of the field development plan.

Agbami project stakeholders are aligned on all technical aspects of the field development plan and the project is rapidly proceeding toward sanction and awarding of major contracts.
Propellant-Actuated Deep Water Anchor
Authors: Taylor Robert J. , Beard Richard M.
Published: October 2008

A propellant-actuated direct embedment anchor is being developed to moor deep ocean surface and subsurface structures. The anchor is designed to have a long-term holding capacity of 20,000 lb. and function in sea floors ranging from very soft sediments to hard rock (basalt) in water depths from 100 ft to 20,000 ft. Anchor flukes were designed for sediments and rock. The sediment fluke uses a new quick keying design to maximize efficiency. A launching system utilizing existing ammunition components was developed that was capable of providing the energy necessary to propel the flukes to the required penetration depths. The anchor has been fabricated and tested on land and in water at 110 ft. The anchors functioned properly during the water firings; short-term capacities in silt using reduced propellant charges were about 45,000 lb. Continued testing under a variety of conditions is planned.

INTRODUCTION

Deep ocean anchorage has long been a neglected area of development. Anchoring requirements for sophisticated structures, weather buoys, surface and subsurface instrument arrays, and any number of other constructions must be satisfied by conventional drag or deadweight anchors, anchors ill-suited to the demands imposed on them in the deep ocean. To help alleviate this problem, the Naval Facilities Engineering Command is sponsoring a program being conducted by the Naval Civil Engineering Laboratory to develop practical direct embedment anchors that are both reliable and efficient for use in mooring deep ocean surface or subsurface structures. Operational requirements for the anchor are that it be functional in water depths to 20,000 ft, have a long-term holding capacity of 20,000 Ib and develop this capacity in sea floors from soft clay to hard rock.

To date, a propellant-actuated anchor has been designed, fabricated and tested on land and in water at 110 ft. During its first in water tests, the anchor functioned properly and held short-term loads of about 45,000 Ib in silt, using reduced propellant charges. Also, the anchor demonstrated that it could be safely and quickly assembled and deployed at sea.

BACKGROUND

Present deep-water installation techniques require continuous at-sea operation through a long time period. Therefore, the installation process is vulnerable to inclement weather. It would be advantageous if improved hardware and procedures were available to ease and speed installation. The solution to this problem, however, encompasses a broad spectrum of considerations. Anchor designs, special appurtenances, connective gear, and special operational techniques are among the more critical areas that need improvement. The single most important consideration is the anchor design because improved anchors can alleviate problems in the other areas. Based upon the operational requirements established in the program objectives, the state-of-the-art and the available time frame, it appeared that this critical mooring problem could be most easily solved through development of a propellant-actuated direct embedment anchor.
The Application of Skimmers, Piston Films,and Sorbents for Open Water Spills
Authors: Bianchi Ralph A. , Johanson Edward E. , Farrell James H.
Published: October 2008

As a part of research and field test programs conducted for the Environmental Protection Agency, American Petroleum Institute, the U. S. Navy', and the State of Massachusetts opportunities were presented to asses s the use of skimmers, piston films, and sorbents in open water spills. This paper presentssome of the results of the work performed for the U. S. Navy and the information drawn from the Portland oil spill. Problem areas that require more work are identified.

A series of test programs were conducted using two oil skimmer s to clean up free slicks of oil simulants, petroleum oil and oil sorbent mixtures in Boston Harbor Channel. Tests were also conducted using a skimmer with sweeps in open waters at the Portland oil spill from July 26 through August 4, 1972.

Several modes of operation were employed. A self-propelled skimmer was maneuvered through free slicks and a skimmer without propulsion was operated beside a U. S. Navy LCVP in Boston Harbor Channel. The latter skimmer was also operated beside commercia1 support vessels on the Portland oil spill to harvest oily weeds, oil sheens with the aid of piston films, and large slicks of heavy residual fuel oil.

An assessment of the skimmers tested and used in the various modes and in combination with piston films and sorbents was made. Preliminary oil spill cleanup guidelines were developed for the assessment and some of the conclusions drawn were as follows:Skimmers can be highly effective in open water on both free slicks, windrows, and on oil escaping from a boom,Sorbents playa valuable role in cleanup in open water in an. unexpected way. They make the slick highly visible to the skimmer operator,Piston films are effective in certain, specific operations. They serve as a polishing action to force a sheen into strips that the skimmer can then harvest and to prevent the spreading of oil during harvesting operations.There is a great need for a transfer system to remove the oil, sorbents, seaweed, and debris from oil skimmers. A film showing the results of the test program and of the harvesting of oil and oil-soaked straw in the Portland oil spill is presented in conjunction with the paper.

INTR ODUCTION

Over the past two years a series of Dynamic Inclined Plane skimmers have been designed and built for the Environmental Protection Agency, the American Petroleum Institute, the U. S. Navy, the Canadian Government, and the State of Massachusetts. Under these contracts a wide variety of tests have been performed.
Progress and Prospects of Marine Mining
Authors: Archer A.A.
Published: October 2008

A great deal has been said and written, particularly in the first decade, about the mineral potential of the sea bed. The demand for most minerals and mineral-based commodities has continued to increase at an approximately exponential rate. A considerable and steadily increasing effort has been devoted to research and development of the new technology needed for marine mining. Nevertheless, with the exception of hydrocarbons, to which only brief reference will be made in the paper, the scale on which marine minerals have been recovered is still very modest. Few minerals are being exploited, and of these sand and gravel appear to contribute the largest proportion of the total value. The paper all discuss the reasons for the apparently slow development of this sector of the minerals industry which, since it seems likely that little if any mining is processing in more than, perhaps, 50 m of water, has hardly got its knees wet. However, plans for the winning of manganese nodules from oceanic depths are now well advanced and large capital sums have been committed. The scale of manganese nodule mining and its possible impact on the traditional sources of the metals concerned will be discussed. The conclusion reached will be that there can be no doubt that the sea bed will become an important source of raw materials that will continue to be consumed at an increasing rate for a long time. It seems almost certain that, at least for many years, marine minerals will help to meet part of the increased demand; they are unlikely to replace land-based sources.

DEFINITION

Marine mining is here defined as the commercial recovery of minerals other than oil and natural gas from the surface of, or below, the sea bed by operations connected only indirectly with the land (i.e., by ships or pipelines). The recovery of minerals and fresh water from sea water, beach mining (even where this extends below high-water mark by the construction of embankments) and the winning of such minerals as coal, iron ore, tin and mercury in the seaward extensions of mines on land are thus excluded. Ideally, minerals recovered from estuaries and coastal lagoons should also be excluded; in practice, this is seldom possible as such operations are not always separated in published data.

THE PRESENT: GENERAL

The number of operations falling within this definition and the number of countries involved are remarkably limited in view of the widespread interest shown in marine mining prospects during the last few years. Indeed, as if to mirror the increasing demand for the minerals concerned, the volume of literature on marine mining seems to be increasing exponentially to the point where it is tempting to suggest that publishing is the largest sector of the marine mining industry.
Metalliferous Muds of the Marine Environment
Authors: Amann H. , Backer H. , Blissenbach E.
Published: October 2008

Oozes with U, Mo, V and Th of the shelf are of no commercial value at present, but are little known and may constitute a future potential.

Metallilerous muds enriched predominantly in Fe and Mn, and with Zn, Cu, Pb, Ag and Cd, originate in shallow to deep waters through water cycling, magmatic activities or a combination of these. The only deposit of this type of commercial interest is in the Atlantis II deep of the Red Sea. The southern part of this deep contains 150 to 200 million tons of mud (dry, salt-free) with about 5 percent Zn and 1 percent Cu. Lilting the mud appears feasible, metal extraction more problematic. Altogether, no definite decision as to an over-all feasibility has been reached.

Prospection methods and tools applicable also to other submarine mineral projects and sea-floor survey have been developed and tested in two cruises in the Red Sea and Gulf of Aden with R/V Valdivia (1971 to 1972). Several new deeps, some with metallilerous sediments, became known. The entire sea-bed area has not been covered adequately for an over-all rating of the mineral potential.

From their origin in an early stage of continental drift, the Red Sea metallilerous muds allow the assumption that such deposits also formed during the respective stages in former geological times and remain to be detected and developed.

MODE OF OCCURRENCE

Mud deposits enriched in metals form on the bottom of the shelf and the deeper ocean where metal supply and biochemo physical conditions of deposition coincide favorably and where little other sediment is admixed. Such muds have not attained economic importance, but may represent large future reserves. The only occurrence already in the range of speculation about its exploitability is the Red Sea deposit of the Atlantis II deep that is discussed in this paper in more detail following a resume of the genesis of metal-enriched deposits of the sea bed in general.

On the basis of different depth of origin and nature of metal supply, the mud deposits can be subdivided as follows:organic-rich muds or oozes of the shelf (metals from sea water Fig. lA) andmetallilerous muds of the shallow to deep sea bed - metals from water cycling (leaching and redeposition); metals from magmatic sources, mostly through volcanism (Fig. 1B); and various mixed types (Fig. 1C). (Abyssal clays or oozes, mostly residual deposits, remain unconsidered, as even the long-term utilization, e.g., substitutes for cement rock or for aluminum ore, is too speculative; compare MERO).

Organic-Rich Muds or Oozes

Organic-rich muds or oozes (Fig. 1A) generally occur on the shelf in shallow basins holding not more than some tens of meters of such sediments and are typically present along the western continental margins of Africa and South America.
Fish Protein Concentrate: The State of the Art
Authors: Knobl George M.
Published: October 2008

Fish protein concentrates (FPC's) may be defined as those products obtained from fish in which the protein is more concentrated than in the original raw material. FPC's may range from light-colored, bland powders to dark powders having intensely fishy tastes, or they may be pastes with a similar wide range of colors and tastes. Both powders and pastes may be water soluble or insoluble and may be high in nutritive value or low in nutritive value.

FPC's may be prepared by a variety of methods which can be classified as chemical (solvent extraction) or biological (enzymatic and microbial) procedures.

During the last 20 years most efforts to make FPC's have involved the use of solvents, usually isopropyl alcohol, and several pilot plants and a few full-scale industrial plants have been constructed. Some of these plants are now in operation. Others were operated for a short time and then, for various reasons, operations ceased.

The biological procedures for making FPC's, in general, have not advanced beyond the laboratory or small pilot-plant stage.

This paper reviews FPC efforts to date and the major problem areas encountered in its utilization.

INTRODUCTION

Fish protein concentrates (FPC's) may be defined as any products obtained from fish having higher protein contents than the original raw material. FPC's may range from light-colored, bland powders to dark powders having intensely fishy tastes, or they may be pastes with a similar wide range of colors and tastes. Both powders and pastes may be water soluble or insoluble and may be high in nutritive value or low in nutritive value.

FPC's may be prepared by a variety of methods which can be classified as chemical (solvent extraction) or biological (enzymatic and microbial) procedures.

During the last 20 years most efforts to make FPC have involved the use of solvents, usually isopropyl alcohol, and several pilot plants and a few full-scale industrial plants have been constructed. Some of these plants are now in operation. Others were operated for a short time and then, for various reasons, which will be presented in this paper operations ceased. The type of FPC produced by solvent extraction of raw fish is usually a bland nearly odorless, lightly-colored, water insoluble but highly nutritive powder, intended for use as a protein supplement.

The biological procedures, in general, have not advanced beyond the laboratory or small pilot-plant stage. The forms of FPC produced by biological methods have the advantage of being water soluble and would likely to be lower in cost than solvent extracted products. However, they may be lower in nutritive value, depending on the process and often retain a higher lipid level with a corresponding stronger flavor and odor.

This paper reviews FPC efforts to date and the major problem areas encountered in its utilization.
Future Directions In Fish Protein Research
Authors: Finch Roland
Published: October 2008

INTRODUCTION

The world catch of fish has increased steadily since World War II from 19.6 million metric tons in 1948 to 69.3 million metric tons.1 Although the ultimate sustainable world catch has been predicted to be two to three times this level,2 the increase in over-all catch, and particularly that used for human consumption, has recently shown signs of slowing down. There are reports of serious local resource depletions that give rise to concern about these predictions. One example is the problem of the great Peruvian anchovy fishery that alone accounted for much of the increase in world landings in recent years. This fishery suffered a serious setback in 1972 because of a decline in abundance and a change in environmental conditions that places the resource beyond the reach of the fleet. Consequently, the government of Peru closed the fishery temporarily.

It is possible that the depletion of these and other important fish stocks are due in some measure to pollution, but the general belief is that the great increase in the capacity and efficiency of fishing operations has been primarily responsible. If any event, we see a limit to the speed and extent with which world fish supplies may increase to meet the needs of the rapidly growing world population.

In the U. S, the picture has been somewhat different. The total domestic catch since 1950 has remained essentially constant between 1.8 and 2.4 million tons, although this gross figure conceals considerable species to species shifts. Imports have increased over the same period from 1.6 to around 6.8 million tons with those in some years, notably 1968, exceeding this. Much of this increase has been in industrial products (fish meal and solub1es) but imports of edible fish have also grown over threefold during this time.

In addition to the factor of fish catch the future of the fish supply available to the U.S. is affected by increases in consumption of fish by other countries. The U. S. is finding itself in increasing competition for the world fishery harvest. For example, in 1971, for the first time Japan outbid U. S. importers for a large amount of shrimp caught in West Africa, India and Southeast Asia with a consequent decrease in imports. The recent increases in trade in salt cod at a time when the world catch of cod is declining has meant the U.S. must bid higher prices to attract imports of frozen cod. With the world tuna catch beginning to peak out, tuna prices rose 20 to 30 percent in 1972. These trends can be expected to continue and provide an increasing problem in meeting the fishery product needs of our own rapidly increasing population.
Studies on Experimental Harvesting and Regrowth of Plexaura Homomalla in Grand Cayman Waters
Authors: Hinman Jack W.
Published: October 2008

The prostaglandins are lipid acids which are important metabolic regulators for all animal species including man.1 Some members of this family of compounds have considerable potential as medicinal agents. 2 Weinheimer and Spraggins 3 reported the is flation of the prostaglandins, (15R)-PA2 and its acetate methyl ester, from the sea whip Plexaurahomomalla obtained from the waters of Florida. More recently a new variant of this gorgonian was discovered in certain Caribbean waters from which (15S)-PGA2 and its acetate methyl ester could be isolated. 4 In addition, two new natural prostaglandins, the lS(S) and l5(R)-5,6-trans isomers of PGA2 (and the corresponding 15-acetate methyl esters), were found. 5 Since these compounds can serve as useful intermediates in the preparation of clinically important prostaglandins, 6 studies were undertaken to determine the ecological and economical feasibility of utilizing P.homomalla as a raw material. These studies-included surveys to supplement existing knowledge on distribution and abundance of the species, harvesting methods, regrowth rates and the influence of harvesting on the reef ecology.

The most extensive studies have been carried out in the off-shore waters of Grand Cayman Island, B.W.I. with the full cooperation of the Cayman Islands Government. A comprehensive review and evaluation of this work was conducted in May, 1972 at an International Symposium organized by Dr. F.M. Bayer and Dr. G.L. Voss of the Rosenstiel School of Marine and Atmospheric Science of the University of Miami. The proceedings of the symposium are being published in StudiesinTropicalOceanography. In addition similar studies have been carried out in the coastal waters in the Bahamas and other islands in the Caribbean. In this presentation I shall try to summarize the more important aspects of these studies, and indicate the trend we see for this research. Two objectives of this project were as follows:Estimate the quantities of P.homomalla available.Develop methods for harvesting which would be ecologically acceptable and would provide maximum opportunity for replenishing the natural supply.

This study was initiated in December, 1970 with the advice, recommendations and active participation of Dr. F. M. Bayer, Dr. Robert A. Kinzie III and Mr. Sid R. Anderson, Jr. Grand Cayman Island was chosen as the study site for the early experiments because of the abundance of P.homomalla, a minimum of logistics problems and because of the interest and splendid cooperation of the Cayman Islands' government. In addition, we were fortunate to enlist the able assistance of Mariculture, Ltd., a research-minded corporation located on Grand Cayman Island. This company is studying the domestication and commercial production of the green sea turtle. They were in a position to provide the boats, divers, pilots, freezer storage, etc. required to make our project feasible.
Navigation Satellites for Geophysical Exploration
Authors: Bybee Hal H.
Published: October 2008

The Navy Navigation Satellite System was originally designed for military navigation by the Applied Physics Laboratory of Johns Hopkins University but is now released for civilian navigation. It consists of six beacon satellites in polar orbits for which the Navy maintains the accuracy of the transmitted navigation data. Several different passive receivers are available for these coded satellite signals.

The navigation mathematics is an iterative process of least squares fitting of the satellite data. At sea discrete position fixes are produced instead of continuous navigation. On land several fixes may be combined to resolve altitude uncertainty. Two different physical interpretations of this data elucidate the geometric basis for the solutions and their accuracy relationships.

The current state of the art in satellite navigation accuracy is only possible because intelligent techniques are being used to counteract the inherent error sources of the system. Special receiver design reduces interference problems. Mathematical modeling removes most of the effects of transmitting the satellite signals through the imperfectly known ionosphere and troposphere. Good dead reckoning alleviates the errors specifically identified with receiver antenna motion.

Although satellite positioning can be used alone, integrating it into other navigation systems produces the best results. The other system produces dead reckoning for the fix computation while the fixes produce calibration factors for the first system. The redundant information between the components of the integrated system increases the accuracy of error smoothing and correction in both real time and postprocessing.

In filling the nitch of sophisticated global position reference, the Navy Navigation Satellite System has proved a boon to the geophysical exploration industry.

INTRODUCTION

The navigation satellites currently being used in geophysical exploration are the Transit satellites making up the Navy Navigation Satellite System. This system was designed to provide world-wide position fixes in latitude and longitude at predictable intervals ten to twenty times a day for multiple users with minimal equipment. Accuracies of 110 feet are being obtained by some users.

This paper covers the basic satellite system from hardware through position fix computation. Various error sources and their impacts on accuracy are examined for "stand alone" systems, "integrated, real-time marine navigation" systems, and postmission processing.

HISTORY

On 4 October 1957, the Russians launched the first Sputnik ushering in the space age. By early 1958 the Applied Physics Laboratory of the Johns Hopkins University had assessed the feasibility of a Doppler shift satellite navigation technique and proposed it to the Navy. December 1962 saw the prototype satellite launched, and by July 1964 the Navy Navigation Satellite System was operational.
The Realities Of Radio Positioning
Authors: Moyer James P.
Published: October 2008

The field of radio positioning has grown from the simple rotatable antenna and AM receiver of the direction finder to a wide assortment of complex electronic systems with a correspondingly broad variety of performance and operational characteristics. The intelligent use of any specific radio positioning system must, therefore, 'require a reasonable understanding not only of its performance capabilities under jdea1 conditions, but also the constraints that determine its true effectiveness in the environment of actual operation. The cost and quality (cost effectiveness) of the positioning end product in the geophysical industry is a direct function of the quality of the numerous interfaces which should exist between the ultimate user and the service organizations providing the geophysical and positioning data. A review of available generic radio positioning systems serves to indicate the need for intelligent system selection and operation. A first order analysis of the interfaces which can exist throughout a routine geophysical mission points out numerous opportunities to improve the end product cost effectiveness by adequate mission definitions, thoughtful mission planning, and operational communications and control. Based upon a general appreciation for the operational mission problems, some specific areas are identified where timely attention and communications are most likely to reap positive benefits for all those associated with the survey.

Finally, current trends indicate that radio positioning systems will provide increasingly satisfactory survey data over at least the near future.

1.0 INTRODUCTION

Survey control for the vast majority of marine geophysical data collection missions is currently provided by a class of navigation systems which can be generically defined as radio positioning. While the low frequency end of these systems (10.2 KHZ) overlaps into the acoustical range and the high end (laser) reaches the visual, all share the common characteristic of producing positioning information based on measurement of electromagnetic signal propagation above the earth's surface, and wholly within the earth's atmospheric envelope. With radio positioning systems operating across such a wide frequency spectrum (distributed into discrete bands by international and national priorities) It Is obvious that even ideal performance characteristics will be quite diverse. In fact, the only generalization of ideal performance ‘the higher the frequency, the greater the accuracy’ can be a tenuous notion in the presence of the operating environment.

Since radio positioning systems play such an important role in marine geophysical activities, a reasonable appreciation of their performance under operational conditions can lead to the production of an improved quality survey end product at reduced cost. Thus, the cost effectiveness of the overall geophysical mission can be significantly affected by the levels of understanding and attention afforded the positioning subsystem in the total mission system.
On the Mechanics of Pressure Ridge Formation in Sea Ice
Authors: Parmerter R.R. , Coon M.D.
Published: October 2008

One of the most strild.ng features of the Arctic Ocean is the pressure ridges, which are linear accumulations of ice rising to several meters above the ocean surface and tens of meters below. These ridges present a formidable obstacle to both surface and submarine shipping and to transportation on the ice surface. In order to better understand these structures, a computer model of the ridge formation process has been developed that generate ridges whose are in good agreement with observed data. This model is described in a paper published in the Journal of Geophysical Research. Experience with the computer model has suggested additional simplifications that yield analytical models of certain features, such as force displacement relations, maximum height of ridges, and location of cracks in the ice sheet. These analytic models are the subject of the present paper. Significant dimensionless parameters are identified, and parametric studies are presented of the functional relationships between these parameters. The maximum height, crack location and required force are found as friction of the mechanical and geometrical properties of the ice sheet. The problem of forming a ridge from a refrozen lead is considered in detail. Initially, the ridge forms from the thin ice of the lead. Once the lead has closed, the ridge building process must either stop or continue by breading ice from the thick parent sheet. Typically, a force increase of two orders of magnitude is required to make the transition from building a ridge from refrozen lead ice to building it from the parent ice sheet. The large forces are toward the upper end of the range of forces available in the ice sheet, in agreement with the observation that most ridges are built from thin ice blocks. When forces are available and the parent ice is fractured, it is shown that ridges of limited height but unlimited lateral extent can occur. These correspond to the hummock fields that are occasionally observed. The proposed models agree with present observational knowledge and provide predictions that can be tested by future field experiment.

INTRODUCTION

From the time of man's earliest travels into the arctic, he has known of the existence of ice ridges. These ridges rise several meters above the ocean surface and may extend tens of meters below. Until recently, however, little has been known of the cross-sectional profile of ridges or of the mechanisms by which ridges are formed.

Knowledge of ridge size and distribution is of interest because ridges present formidable obstacles to both surface and submarine transportation systems. The forces required to form ridges are an important part of the rheological behavior of pack ice since the compressibility of the pack is determined, in part, by the formation of ridge structures.
Ice Model Testing
Authors: Biewer F.N. , Grinius V.G. , Hammett D.S.
Published: October 2008

The characteristics required of an ice model in order for model testing to yield meaningful results are discussed. The various materials that have been used for ice simulation are examined for their applicability in the offshore areas of interest. The problems associated with obtaining scaled values of the mechanical and elastic properties are cited. The author list the for the synthetic ice model that was developed and a number of photographs of the ice testing are included.

INTRODUCTION

The opening of the ice regions of the globe to oil exploration and production has placed a requirement on the testing laboratories and facilities for model testing of equipment in an ice environment. In the past the interest in ice in the commercial field was restricted largely to icebreakers in opening routes through the ice fields for the passage of ships engaged in commerce. The epic journey of the Manhattan in 1969 seeking routes and methods for the economical, safe, and efficient transport of Arctic oil to the commercial markets represented full scale experimentation by the petroleum and shipping industries. Model testing was utilized extensively in the design of the Manhattan and several of the current ice model testing techniques were developed as a direct result of the requirement to test models of the prototype ship. Ice model testing, however, remains as a new and challenging task for the model test basins.

REQUIREMENTS FOR THE ICE MODEL

Rather than discussing the highly technical aspects of ice modeling and repeating the excellent work of others in describing ice, it is appropriate to concentrate rather on the problems associated with creating a proper ice model. For those desiring more detailed information on ice itself, a brief bibliography has been appended. Model work has as its objective the re-creation or simulation, at a ratio less than unity, those features, properties, or characteristics which are important in the investigation at hand. Certain scaling laws, when properly applied, will enable the testing laboratory to predict prototype performance with an accuracy which is satisfactory for prototype design.

The model ice which is used may be either real ice or it may be a synthetic material. The nature of the material itself is not a fundamental requirement but the properties of the materials are basic to the study. Using accepted testing techniques we are required to scale properties such as flexural strength, compressive strength, shear strength, and modulus of elasticity of real ice in order to arrive at a-model ice. If a model scale of 1:50 is used with Froude scaling, the real ice properties listed above must be multiplied by the model scale, 1. e., 1/50, to give the properties of the model ice.
Wave Induced Pressures on a Submerged Horizontal Plate
Authors: Durgin William W. , Shiau Jong C.
Published: October 2008

An analytic method is presented whereby the differential pressure distribution on a submerged horizontal flat plate, 'induced by the passage of gravity waves, can be calculated. Plates having cord lengths of the same order of magnitude as the wave length are considered, making the analysis applicable to large offshore structures. The results of an experimental program, designed to test the validity of the theory, are presented and show good agreement.

In the analysis, the plate is imagined to be rigidly suspended at an arbitrary fixed depth and then replaced by a vortex sheet whose strength varies both temporarily and specially. The velocity potential of this sheet is adjusted such that, when combined with the potential of the oncoming waves, boundary conditions on the plate, the free surface, and the bottom are approximately satisfied. The final vortex strength distribution can be determined allowing the velocity field and hence the pressure distribution on each side of the plate to be calculated.

The experimental program was conducted using 4 × 4 × 40 ft. flume with a generator capable of producing waves having a broad frequency and amplitude spectrum in varying water depths. A flat plate of sandwich type construction was instrumented with small pressure transducers whose outputs were processed and recorded on an oscillographic recorder. Results are presented as instantaneous differential pressure distributions for associated wave positions, sequentially as the wave progresses. Analytic and experimental results are compared and show good agreement.

An advantage of the analytic approach is that pressure distributions as well as total forces may be readily obtained. This is important in designing a structure against maximum local differential pressure. The method can be extended to more complex shapes and finite length plates.

INTRODUCTION

The prediction of forces, or more precisely, the pressure distributions, experienced by submerged structures due to the passage of gravity waves has become important with the advent of large offshore structures. If the size of a structure is small compared to the wave length then the forces can be evaluated by the assignment of suitable drag and inertia coefficients using an approach similar to that of Morison (5) in which case it is necessary to determine the coefficients experimentally for any given geometry (2). If the size of the structure is a significant fraction of the wave length the above method is invalid and a more complicated analysis such as the diffraction theory of Garrison and Rao (1) is needed. Unfortunately, the application of diffraction theory for a given geometry is exceedingly difficult unless one assumes the structure size is small compared to the wave length, which may not be realistic.
Computerized stress Analysis of All - Metal Marine Loading Arms
Authors: Gallo D.J. , Forbes D.J. , Huebsch P.J.
Published: October 2008

Over the years the means used to transfer petroleum cargo between ship and shore have evolved from all-hose assemblies to the present all-metal, double counterweighted marine arm.

With recent trends toward larger tankers, higher cargo transfer rates, and more demanding operating specifications, arms have become bigger (10-inch to 24-inch diameters and 100 feet long) and far more structurally complex. Stress analysis of these arms is more demanding because of the spatial and frequently indeterminate nature of the arm structure. Except for the simpler, early 1960 vintage arms, stress calculations are tedious, time consuming, and often, of necessity, imprecise.

Consequently, Esso Research has developed a computer program capable of rapid and exact arm analysis. In a single run, the program automatically applies a range of loading combinations and utilizes a stiffness matrix technique to calculate stresses in all members of the arm. The analysis can be made with the arm in a variety of attitudes including: stored maneuvering, operating, maintenance, washing, and hydrostatic testing.

The following areas are covered: the criticality and complexity of loading arm design, the three-dimensional stress analysis required, and the computer program developed to examine arm stresses.

INTRODUCTION

One of the most common means for transfer of petroleum cargoes at conventional tanker berths is the double-counterweighted, all-metal marine loading arm. It is a three-dimensional articulated structure consisting of a fluid carrying piping system stiffened with pinframed or rigidly connected structural members on one or more of its basic components. At least six swivel joints in the fluid-carrying piping allow the arm to be maneuvered from a stored position to and within an operating envelope.

The all-metal loading arm has evolved over the last 25 years from the simplistic manual and semi-automatic hose systems shown in Illustration 1. Some of the shortcomings of these early systems, which spurred development of the double-counterweighted arm, are:All-hose structureslimited loading ratedifficult handlingcontinual adjustment to maintain proper hose bend radiusHalf-hose/half-pipe armscontinual adjustment to maintain proper hose bend radiusAll-metal, freestanding armslarge reaction imposed on tanker's Manifold

For the most part, however, these systems presented few difficulties for the design engineer. While stress analysis of the prototype arm shown is complicated by its three-dimensional nature, the loads can be hand calculated throughout the arm by using the equations of statics.

Over the past seven years loading arms have steadily increased in size. Arm reach (total length of inboard and outboard tubes) has extended from 46 feet to 100 feet to keep pace with the growth of tankers from 50M dwt to 300M dwt. Another factor contributing to longer arm reach is the wider range of vessels loading arms are required to service.
A Mediterranean Sea Wave Spectral Model
Authors: Pore N. Arthur , Stevenson Norman M. , Cardone Vincent J.
Published: October 2008

An operational Mediterranean wave spectral model has been developed through the cooperative efforts of the U. S. Naval Oceanographic Office (NAVOCEANO), Fleet Numerical Weather Central (FNWC) and New York University (NYU). Since April, 1972, the model has been operating in a real-time environment (analyses/prognoses to 48 hours). The model is a modified version of the original NYU North Atlantic wave model and has two main parts:wave energy growth based on a modified version of the Miles Phillips growth mechanism and dissipation at individual grid points andwave energy propagation from grid point to grid point. 'The Mediterranean wave model uses a conic conformal grid, permitting the assumption of equal spacing between grid points. There are 455 sea points with a mesh length of 67 km.

The wave model driving force is a modified version of the FNWC marine wind model that has a mesh length of approximately 370 km. For use in the Mediterranean, the winds are interpolatec between marine wind field grid points. At analysis/preanalysis times, wind reports from synoptic ship files are reanalyzed in the Mediterranean wind program so that local wind phenomena, such as mistrals, are included in the wind field.

The Mediterranean wind and wave model was evaluated with ship reports, one wave buoy and an airborne wave laser. The wave computations appear to be as good as the wind input allows.

The on-time analyses and 24-hour forecasts of wave heights are transmitted to Fleet Weather Central, Rota, Spain.

INTRODUCTION

A Mediterranean wave spectral model has been developed through the cooperative efforts of the U. S. Naval Oceanographic Office (NAVOCEANO), Fleet Numerical Weather Central (FNWC) and New York University (NYU). Since April, 1972, the model has been operating in a real-time environment (analyses/prognoses to 48 hours). The Mediterranean wave spectral model is a modified version of the original NYU North Atlantic wave model and has two main parts:wave energy growth and dissipation at individual grid points andwave energy propagation from grid point to grid point.

WAVE SPECTRAL MODEL

The growth of wave energy in this model is accomplished with an equation that combines modified versions of the Miles instability theory and. Phillips resonance mechanism. 2 The model evaluates all computed spectra to ensure that the calculations never exceed the limits of the Pierson-Moskowitz4 fully developed spectrum for the given wind speed. For computational purposes, the energy spectra are broken into matrices of 15 frequency bands by 12 directional bands as shown in Table 1. The energy in all the frequency bands except the highest frequency band are propagated through the grid system by a "jump" technique.
Consideration of Freak Waves for Design of a Jack-Up Structure
Authors: Schellen Thomas E. , Jahnke Thomas , Künzel Jochen
Published: October 2008

To ensure adequate safety of marine structures in extreme weather, it is conceivable that standards are needed that account for the characteristics of ultimate limit seastates based on wave conditions with a return period higher than 100 years. Such standards must include an analysis of the reserve strength available when a marine structure is subject to an extreme event of a freak wave. For the generation of freak waves traditional potential flow methods are not well suited to accurately predict wave loads, because phenomena such as wave run-up on the structure’s legs and impact-related loads on the hull are not accounted for. Therefore, wave effects were predicted with advanced computational fluid dynamics techniques. The purpose here was to determine the safety level under freak wave conditions. We selected a typical mobile self-elevating drilling unit stationed the North Sea and investigated its structural response under survival conditions and, in addition, under two extreme wave conditions representing freak waves. Based on a comparison of the resulting stresses with the structure’s rule based design capability, we assessed the reserve strength capacity still available under freak wave conditions.

Introduction

Marine structures, such as mobile offshore drilling units, are designed to operate at different locations throughout the world under varying environmental conditions. To assess their structural strength and design safety, two loading conditions are generally investigated, namely, the operating condition and the survival condition. For both loading conditions, the unit’s operating manual generally specifies limiting environmental parameters, such as maximum wave height, current velocity, and wind speed for the given water depth. It is assumed that these environmental parameters are known for the operating location of the rig and that weather forecasts are reliable enough to allow sufficient reaction time to prepare for worsening weather conditions.

Weather forecasts do not give notice of freak waves arising under extreme weather conditions; that is, such waves occur unexpectedly. The occurrence of a freak wave could be treated as an accident, similar to an earthquake. From this point of view, it would be rational to require the structure to remain standing and that critical structural components remain intact to prevent global failure. Under these circumstances, with all safety factors equal to 1.0, plastic deformation may be acceptable to avoid failure (ultimate strength).