bluuebunny/crossref_metadata_2025 huggingface dataset:
Field Tests Of Adeep Ocean Cable Burial Concept
Authors: Rockwell Phil K. , Engel John H. , Piercy William B.
Published: October 2008

Bottom fishing equipment routinely damage or break important Navy oceanographic cables resulting in substantial repair costs and unacceptable interruptions. The Civil Engineering laboratory (CEL), sponsored by the Naval Facilities Engineering Command (NAVFACENGCOM has developed and validated an engineering concept for a Deep Ocean Cable Burial (DOCB) system. The DOCB system provides an effective and reliable means of burying cables 3 ft deep in ocean sediments, at speeds greater than 1 knot, to water depths of 6,000 ft.

The DOCB system concept is a remotely controlled machine which under runs and buries existing (previously laid) cables. It is powered and controlled from a surface ship via an electro-mechanical umbilical cable. The machine is self-propelled by ducted thrusters and supported on water lubricated skids. The excavation system comprises an orbital vibrating plowshare and a vertical water jet. This paper presents the results of full scale field tests at CEL on the excavation and skid systems.

Full scale field testing of individual components as shown that a 70% reduction in drawbar force was achieved by applying an elliptical orbital vibration. It was also shown that the vibration feature would split or push aside buried rocks which would have stalled a conventional stationary plow.

The water jet tests demonstrated that a 2-1/2" nozzle cuts 36" deep in 1-2 psi of clay at a nozzle pressure of 75 psi and flow of 1200 gpm. Also tests with the skid system showed that forcing a layer of water between the skid and soil reduced the skid/soil drag by 50% in both sand and clay.

INTRODUCTION

Oceanographic cables laid on the seafloor have proved to be vulnerable to damage and ensuing failure from the otter boards of bottom fishing trawlers. The Civil Engineering laboratory, sponsored by the Naval Facilities Engineering Command initiated a development effort to synthesize a concept for a system to effectively bury the cables 3 feet deep in the seafloor to ocean depths of 6000 feet. The Deep Ocean Cable Burial (DOCB) concept (Figure 1) comprises ducted thrusters for propulsion, water lubricated skids, and two excavation means - a vertically impinging water jet followed by an orbitally vibrating plowshare, as well as a variety of other supportive subsystems.

Of all the subsystems which are required for the DOCB system, only the orbital vibratory plow, the vertical water jet, and the water lubricated skids had not been proven in situations similar to those that would be encountered during a cable burial operation.

Vibratory plowing as a means to create a trench for burying cables was selected as one of the primary excavation subsystem candidates during the DOCB concept development.
Offshore Crane Dynamics
Authors: Clarkson John A. , Kenny Francis M.
Published: October 2008

The environments in which offshore cranes operate generate a number of factors which determine that the loadings on the structure are essentially dynamic in nature and not static as has been commonly used in design in the past. This paper presents the nonlinear equations of dynamic equilibrium and a method of solving these equations. From the theory developed a typical crane is analysed and the general trends of behaviour are discussed.

INTRODUCTION

The development of the offshore industry in the North Sea originally relied heavily upon their American counterparts for the supply of the relevant technology. However, experience rapidly showed that the operating conditions in the North Sea were significantly more severe for most of the year than existed in the Gulf of Mexico or on the Californian coast. Consequently the level of technology required to overcome many of the problems still had to be developed as the problem areas became identified. One of the very significant areas in which the environmental demands exceeded the then current design capability was in the design and operation of the offshore cranes.

The platform cranes are a vital link in the operation of the platform, not only during the fabrication and drilling stages but also during the production phase. The financial penalities which might be incurred by the operator due to any shortcomings of the cranage facilities can be enormous.

The crane structures which were originally used in the North Sea were derivatives of land based cranes and were drastreally under-designed for the duties they were expected to perform. These shortcomings were manifested by a number of assorted structural failures which resulted in the cranes being inoperable for extended periods and also led to the loss of many lives of crane drivers. Until January 1979 there were 10 fatalities in the North Sea which were directly attributable to crane operations and failures. This number of fatalities was second only to the 19 diving fatalities, an occupation which most people consider to be many times more dangerous than crane driving.

The outcome of these failures was a derating of the crane duties to levels which were significantly below those originally specified. The type of global derating carried out still indicated a lack of appreciation of the exact nature of the root cause of the problem. This statement is supported by the fact that failures still continued to occur in crane structures.

A significant number of crane structures operating in the North Sea were designed upon the principles of static structural analysis. This type of design philosophy has shown an inadequate appreciation of the loading conditions which these structures are subjected to during their operating lives. Unlike land based cranes where the lift can be made as slowly as the driver cares, and from a stationary surface, the offshore crane driver needs to be able to lift as quickly as possible to clear the load from the deck and the deck crew.
Processing Of Pacific Ocean Manganese Nodules
Authors: Itoh Hiroshi , Okuwaki Akitsugu , Okabe Taijiro
Published: October 2008

An acid leaching process of Pacific ocean nodules has been studied. Nodules were leached with 0.1-3.5 N sulfuric acid at 70-90°C for 2-30 hours. Kinetics of copper and nickel extraction was discussed. Nickel and cobalt were recovered from the leaching solutions with hydrogen sulfide or by the cementation under pH control using ferromanganese and iron. Nickel was successfully separated from cobalt by solvent extraction with LIX 64 N extracting system adding a small amount of sodium sulfite.

INTRODUCTION

In Japan, as well as in other advanced nations, Pacific ocean nodule development is an interesting subject. In Japan, consumption of copper, nickel and cobalt has a large share in the world, and depends almost on the foreign resources. In future, Pacific ocean nodules will be major resources of the metals for Japan.

Since 1970, the basic and field experiments of the continuous line bucket mining system proposed by Masuda, have been made mainly in National Research Institute for Pollution and Resources of Japan (NRIPR). Japanese Manganese Nodule Develop Co. and Deep Ocean Mining Co. have been established for nodule mining in Japan. The Deep Ocean Mineral Association of Japan (DOMA) constructed the Hakurei Maru, a vessel for the cruise of nodule research. Japanese several company?s are joining in such international consortia of nodule development as Kennecott Joint Venture, Ocean Management Inc. and Ocean Mining Associates. The metallurgical research of Pacific ocean nodules, in Japan, has been conducted by Tohoku University, Fukushima Technical College, Yamaguchi University, NRIPR and so on.

As far as the metallurgical processing of nodules, hydrometallurgical process is generally believed to be more profitable than pyrometallurgical process. However, each consortium has selected a different process. Kennecott Joint Venture proposed an ammonia leaching process (Cuprion process). l Ocean Mining Associates selected a hydrochloric acid leaching process. 2 Ocean Management Inc. preferred a pyrometallurgical process. 3

It is preferable, especially for Japan, that the metal concentrates or metal products are made from nodules in a floating plant (a process plant on floating structures) at the sea-area where they are being mined, or on a floating barge at an island's coast near the nodule area, mainly to save transportation cost. In the first step of nodule development, metal sulfide concentrates Or cemented metals should be commercially produced in the floating plant and fed into an operating smelter.

Several hydrometallurgical processes for manganese nodules were evaluated by the present authors and reported in the Japanese literatures. 4–15 Processing at sea on a floating or sea-moored barge seems to provide several advantages, but a simple process is required for easy operation and maintenance.

A sulfuric acid leaching process, operated at temperature below 100°C in 2-3 N acid concentration, may be well suited to these requirements.
Loads And Motions Of An Aritculated Loading Platform With Moored Tanker
Authors: Naess Arvid
Published: October 2008

The paper highlights the contents of a report containing the results of extensive model tests of an articulated loading platform (alp) both with and without a tanker moored to it. These tests were performed under wind, wave and current conditions and were done at a scale of 1:70. The alp model was of a tubular structure type (see Fig. 1), and its full scale counterpart was meant to operate at a depth of about 150 metres. The scale model of the tanker corresponded to a 150.000 dwt tanker. In our paper we shall present response amplitude curves for forces and moments along the alp column, together with the hawser tension. The motion responses of the system will also be discussed. A hydrodynamic damping coefficient for surge motion of the alp-tanker system is also given. We shall finally discuss some scale effects, especially vortex shedding from the alp, which is more pronounced in model scale than in full scale.

1. INTRODUCTION

In recent years the single point mooring offshore loading terminal has seen an increasing application in the exploitation of North Sea oil fields. Parallel with this, the developing of computational methods for predicting motion and load responses of this type of marine structures has become necessary. And the number of papers published on these matters over the last few years, clearly reflects the increasing activity in this field. It is, however, a fact that most of the experimental work carried out on particular designs are done on commission and therefore confidential. A consequence of this is that very little experimental data are accessible to research workers outside the companies who own these data.

At the Ship and Ocean Laboratory (SOL) in Trondheim, we have on commission carried out several extensive model testing programmes of single point mooring loading terminals. But as the experimental data from these tests were the property of the commissioning companies, we have not previously had any opportunity to publish any of these data. We are, however, now in the fortunate position to be able to publish the complete test results from rather extensive model tests of a single point mooring articulated loading platform (spm-alp) designed to operate out in the North Sea. And in the present paper we shall give some of the most important results from these model tests.

The test programme was carried out in Wave Tank no. 1 at SOL. It has dimensions 175m × 10.5m × 5.8 m (length × breadth × depth). The complete programme consisted of 31 different tests both with and without a tanker moored to the spm-alp and under various environmental conditions.

During the tests all motions of the alp and tanker were measured and recorded, and the alp was equipped with specially designed transducers at four different locations along the structure to allow measurements of shear forces and bending moments.
Special Mooring Systems Using Remote Controlled Quick Disconnects For Beaufort Sea Drilling Operations
Authors: Lasch James E. , Pearlman Michael D. , Riotte Erich C.
Published: October 2008

In the early 1970's InterOcean Systems, Inc. developed a remotely controlled rig anchor release (RAR*) to provide an anchored drilling vessel with the ability to remotely (by sonar signals) and rapidly disconnect its anchors without cutting the anchor cables. This paper describes the special mooring systems utilizing the RAR for Beaufort Sea drilling operations. These systems have been utilized by Canadian Marine Drilling, Ltd., the drilling subsidiary of Dome Petroleum in their Beaufort Sea operations.

Because of changing ice conditions which occur in the arctic, and because of the stringent Canadian government regulations, it was necessary and desirable for Dome Petroleum to provide special mooring systems on their drilling vessels which included an RAR on each mooring line. This system provides a rapid means of disconnecting in the event pack ice forces the drilling vessel off the well.

Several mooring configurations were tried, modified, and simplified to improve their performance over the course of the four years (1976 through 1979) of actual field use. The paper describes the mooring systems, the RAR units, the installation, testing, recovery and re-installation techniques. The release units are equipped with a status monitoring system which is described together with the experience of, its use with the mooring system.

Economic and safety advantages are discussed. Future uses and potential value of the mooring systems are presented, with examples of applications in other areas.

Introduction

In the early 1970's InterOcean was approached by a drilling contractor to see whether or not it could provide a quick release unit for floating drilling rigs, in particular, semi-submersibles. With its long experience in remote controlled release mechanisms InterOcean Systems developed the RAR which is used in the North Sea, in the Laborador coast area and in the Beaufort Sea drilling operations.

With the beginning of drilling operations in the Beaufort Sea using drilling vessels, numerous special needs were recognized. Among these was the need for special mooring systems for these drilling vessels.

The prevailing ice conditions in the Beaufort Sea and the stringent Canadian government regulations dictated a special system to hold the vessels on position and yet permit rapid disconnection from their anchors in the event of moving pack ice.

InterOcean had developed the rig anchor release (RAR) which proved capable of surviving the rigors of the mooring lines on drilling vessels. Thus, this system was selected and has been used on the Beaufort Sea drilling operations since the drilling program started in 1976. The mooring systems have undergone modification to meet the changing needs in this hostile environment and the RAR has proven sufficiently adaptable to meet the changing requirements.

Originally, the drillships were equipped with underwater fair1eads for each mooring line. These were to reduce the contact of the ships mooring system with the ice.
Seismic Source Decomposition
Authors: Stoffa Paul L. , Ziolkowski Anton L.
Published: October 2008

We exploit the differences that exist between the radiation fields of a point source and an array to design a marine seismic source with desired power spectral and directional characteristics, whose far-field time signature is known precisely from measurements.

The desired power spectral characteristics are created by firing a series of point source units sequentially, such that their time signatures do not overlap. The effective power spectrum of the whole series of signatures can be made equal to the sum of the power spectra of the individual signatures, and can therefore be designed to suit the desired application by an appropriate choice of source units.

The key to the subsequent processing of the recorded data is to measure the pressure wave generated by each point source unit with a hydrophone placed closeby, but in the linear radiation field. The position of this hydrophone relative to the source unit must be known accurately in three dimensions. The depths of the source units and their relative spatial positions at the instants of firing must also be known. From these measurements the far-field signature of the sequence in any azimuth can be deduced, and the impulse response of the earth can therefore be recovered from the recorded reflection data.

The desired directional characteristics can be created by arranging the source unit separations such that each source unit reaches the desired position at the prescribed firing instant. The deconvolution of the derived sequence of signatures simultaneously performs the source array simulation.

Introduction

In the seismic experiment the measurable response x(t) is regarded as being composed of the impulse response of the earth g(t), convolved with the far-field signature of the seismic source s(t), plus some noise n(t). Thus:

(1) x ( t ) = s ( t ) + g ( t ) + n ( t )

where the asterisk * denotes convolution.

The object of initial data processing of the measurements is to recover the earth impulse response g(t) from the measurable quantity x(t) with as high a degree of fidelity as possible. In order to do this there are three basic requirements which must be met :The signal-to-noise ratio must be large.The frequency bandwidth of the generated far-field signature s(t) must be broad.The shape of the far-field signature s(t) must be known. This means that both the amplitude and phase as a function of frequency must be known.

All these three requirements are met if the seismic source produces a high-energy, broad bandwidth signature of known shape. In attempting to meet the first two requirements at sea, with seismic source arrays, it is usually the case that the third requirement is not met. In this approach we aim to meet all three.

Marine Seismic Source Arrays

The marine seismic sources currently in use are of two types: point sources and arrays. Point sources are those which have dimensions which are small compared with the wavelengths of seismic radiation which they generate.
Controlling Iceberg Roll/Stability During Towing Around Drillships
Authors: Benedict C. Peter , Lewis John C. , Dinn Gary J. , Learning Frederick R.
Published: October 2008

Positive and effective management of icebergs around drill rigs on the Canadian East Coast is limited by deficiencies in iceberg handling icebergs roll under tow. Anchor handling tugsare delayed by three to six hours while redeploying towing gear. The troublesome bergs are normally in the range of 50-500,000 tons. Conventional floating polypropylene towing hawsers compound latent instabilities by applying a torque component (other netlike towing geometries control roll for only smaller bergs but tangle during deployment and recovery).

Field iceberg survey data was collected and on the basis of Lagragian computer analysis a large sample of simulated bergs were towed from random stable floating positions. Through these energy formulations the maximum "critical" tow force (before roll) was computed and the results showed:Calculated critical forces agreed with apparent bollard pull normally causing roll.Critical force varied widely for a specific berg depending upon tow bearing.Critical forces change completely when the iceberg settles to a new attitude.Iceberg drafts vary as much as 25% depending upon attitude.

This paper presents:The results on instrumenting iceberg tow forces on the Aquitaine site during the 1980 drilling program,An operational procedure for predicting critical tow forces on the basis of pre-tow surveys.

Introduction

Canadian East Coast drilling is limited to as few as 60 days per year by ice conditions. Only after pack ice clears in July does the short 60-120 day operating window open for offshore drilling.

In the most northerly active acreage Aquitaine et al. are drilling in 1200 feet at the Hekja site in the Davis Strait with the Ben Ocean Lancer1 In preparation for testing Hekja, improvements in equipment and procedures in 1980 enhanced environmental control in these areas:telemetering current data to predict and compensate for the onset of up to two knots current,automated iceberg plotting and trajectory predictions,computer prediction of maximum allowable bollard tow force for iceberg towing with,tensiometer monitoring of actual bollard pull.

This paper reports the results achieved in items c and d.

Around the drillships iceberg are cleared away by standard towing procedures, 3. Near Hekja, the Zapata supply vessels FREEDOM SERVICE and PIONEER SERVICE were used to circle each berg with 3/4 mi. of floating polypropylene rope, catching the forward end and gripping the iceberg at the rear water line. Following the attachment procedure (taking about one hour) the captain would apply 10-110 tons of bollard pull. A major difficulty then arising is that many bergs are of low stability and will roll, slipping the tow hawser.
Snap Loads And Bending Fatigue In Diving Bell Handling Systems
Authors: Liu Francis C.
Published: October 2008

Introduction

Recent at-sea tests conducted by the Civil Engineering Laboratory (CEL) 1 have found that a suspended object with a low submerged weight and a large virtual mass such as a diving bell is highly susceptible to snap loads in a single lift line system. Tensions as high as seven times the payload weight were measured 'in sea state 2. Such high tensile loading could cause a catastrophic failure in the handling line when the breaking load is exceeded. Since the snap load is basically an impact load, the amplitude is expected to be proportional to the payload mass and the relative velocity of the payloadwith respect to the surface excitation velocity. Therefore, higher snap load tensions are expected for diving bells which have larger volumes and/or operate in higher sea states.

Bending fatigue is another problem that is closely associated with the design and selection of a critical lift system such as the diving bell handling system. With such systems, protracted payload suspension over a sheave in the water column is expected. In this mode, the line may fail under repeated snap loads of much lower level than the rated breaking strength of the rope. For fiber and wire ropes, bending fatigue is directly related to external fiberto- sheave abrasion and to internal fiber-to-fiber abrasion. No analytical method is available to predict the fatigue life of a rope/sheave system. Laboratory testing is the only means to generate design data. This paper presents the results of an investigation conducted in 1979 to examine the probability of snap load occurrence, the amplitude of snap loads, and the safety of existing diving bell handling systems. A computer analysis, a sea test, and a laboratory simulation test were made for the U. S. Navy Two-Man Open Diving Bell (ODB). Computer methods were also applied to analyze the handling system of the Deep Diving System/Personnel Transfer Capsule (PTC).

The Open Diving Bell (ODB) is essentially a shallow-depth submerged elevator in the water columnto accommodate divers equipped with air/gas supply equipment or hoses. The ODB consists of a hemispherical acrylic dome structure over a diver's transfer stand. It permits compressed air diving to 190 feet and mixed gas diving to 300 feet. For mostoccasions, the diving bell is operated in sheltered areas such as harbors. However, its applications are not limited to calm waters. The ability of the topside deck hands to work safely and effectively will be the controlling factor in stipulating the maximum operational sea state. The ODB manual2 calls for a handling line of non rotating rope capable of handling aload of 4,300 pounds with a safety factor of five. In the past, the diving bell has been handled by a system consisting of the ship capstan, any available standard sheave blocks, and a variety of ropes including 5- to 6-inch-circumference nylon 2-in-l braids and 1/2- to l-inch-diameter wire ropes.
An Advanced Design Deep Sea Mining System
Authors: Welling Conrad G.
Published: October 2008

In October and November 1978, an advanced design deep sea mining system was tested on the ocean floor at approximately 5000 meters depth. The test was conducted from the Glomar Explorer which had been modified to accept the special design system. The miner design, using the latest available technology, was configured to test concepts that provided for efficient operations. The concept included all the functions believed necessary for efficiency with a multiple of sensors to provide real time information to a control station on board the mining ship. The operators in the control station in turn operate the miner by remote control. The miner is self-propelled with variable speed and fully maneuverable. Controls include: speed and direction, depth of mining cut, rate of pickup, and slurry feed rate. Other controls include: washing and crushing of the nodules, lights for T.V. cameras, high resolution sonar and electrical power.

The system can be divided conveniently into seven basic subsystems: the miner, the flexible link, the buffer equipment section, the vertical pipe with cables, the ship platform, the ship control system and the miner control center.

The at-sea test was made to obtain operational and engineering data on the system. While certain deficiencies were encountered, none were considered basic. Sufficient information was obtained to prove the basic system was viable and would provide the necessary mining efficiency.

Introduction

The design of the Advanced Deep Sea Mining System evolved over a period of years. Systematic studies involving operations research and system analysis were used to determine the necessary functions required for efficient operations. Mining involving large tonnages is basically a materials handling problem. In order to obtain high efficiency the system must be designed to operate under steady state conditions, avoiding where possible fluctuations in material flow rates. This implies full responsive controls for a large integratedsystem. Of course, this does not represent anything unique. Many examples can be cited in land mining operations such as the continuous coal mining machine vs. drill and blast.

The basic problem facing the future nodule miner is the remoteness and size of the nodule ore body and, therefore, the difficulty of obtaining detailed information on its physical nature. Even though extensive prospecting and exploration of the Pacific Clarion-Clipperton nodule belt has taken place, one can only describe the ore body on a statistical basis. There are sufficiently large variations in nodule grade and abundance and bottom topography to place rather extensive demands upon the operationalcharacteristics of the miner.

In the initial phases of making design trade-offs, it became apparent that there was economy of scale in design, that is, designs that achieved annual tonnages of three to four million dry tons per year had considerably lower unit costs per ton than those designed at approximately one million tons.
A Study on Estimating the Relief of Magnetic Basement
Authors: Suh Sang Y. , Hyun Byung K.
Published: October 2008

A new method of estimating the relief of the magnetic basement is designed. In the method, the pseudo-gravimetric anomaly, which is vertical derivative of the pole-reduced magnetic potential, is calculated. The pseudo-gravimetric anomaly is downward continued up to the predetermined mean depth of the basement, and then converted to the equivalent distribution of surface densities. The variation of surface densities at the mean depth gives the relief of the magnetic basement. A model study for a two dimensional case is also given.

Introduction

The problem of magnetic interpretation to geophysicists may be said to consist in finding the distribution of magnetized material whose magnetic field is given on a plane surface. Therefore, we are confronted with the inverse problem of potential field theory, i.e., of determining the source from its potential.

An approach to solve the problem is to select the dimensions and magnetic properties of a subsurface model so that its magnetic effect agrees as closely as possible with the observed anomalous pattern. This procedure is relatively simple. But it becomes more complicated if more than one simply shaped body is evidently responsible for the measured anomalies which anybody trying this has experienced for himself.

Hahn (1965) has introduced a method of estimating the relief of a layer with homogeneous magnetization and a surface relief capable of producing the measured anomalies. The magnetized bodies within his task of geological investigation are assumed to be crystalline rocks showing a sufficiently high degree of metamorphism, and/or intermediary to basic igneous rocks. The complex of these rocks may be represented by some sort of a layer with a more or less constant magnetization and a surface relief which is responsible for the magnetic anomalies. His method gives the relief by using the concept of "relief wave" assuming the direction of the magnetization is same as that of the earth's field.

In this paper, we would like to introduce another approach to find the relief of such a layer, without assuming the direction of the magnetization. This does not mean that the present method gives the solution without knowing the direction but it rather means that we can find the solution, at least theoretically, if the direction of the magnetization, which may be different from the present earth's field, is known.

Our method uses "pseudo-gravity" the concept of which can be found in some literatures (Baranov, 1957). The pseudo-gravimetric anomalies, which are slight modification of Bhattacharyya's pole-reduced magnetic potential, are downward continued up to the predetermined mean depth of the basement. These are converted to an equivalent stratum, i.e., an equivalent distribution of surface densites. The variation of surface densities at the mean depth gives the relief of the magnetic basement.
Flash Butt Welding for Large Diameter Pipes
Authors: Muesch Hermann , Langer Jochen , Dueren Carl F. , Luegger Horst
Published: October 2008

For economic reasons, large-diameter pipes with wall thicknesses of up to 40 rom are most suitable for Jmethod deep-water pipelaying. The welding process chosen is a modified flash butt welding process with inductive preheating. The suitability of this process was proven by means of a prototype machine designed for welding X 60 pipes of 3011 diameter and 40 mrn wall thickness.

Numerous tests were carried out in order to optimize the welding parameters and to analyse the various influencing factors. The results have shown that the modified flash butt welding process incorporating a process of inductive normalizing the weld regionproduces high quality welds which fully meet the requirements of offshore pipelining. A condition is, however, that only pipes with a high degree of purity are employed.

Good reproducibility of the results is guaranteed thanks to the welding machine being automated with a preprogrammed welding process.

1.Introduction

Due to the ever-growing demand for energy, offshore oil and gas exploration has been extended to areas with water depths up to 2000 m. The most economical method for handling gas is the pipeline. However, the pipeline is also frequently an economic and safe solution to the problem of oil transportation.

In recent years, various studies have shown that of all the possible pipelaying techniques, the J-method offers the most advantages for large pipe-diameters or depths below 600 m.

These studies were carried out by a West German team which received financial support from the Federal Minister for Research and Technology. 1/

The results of these studies were published in the OTC in 1979. 2/ The new pipelaying method requires an economic welding technique which ensures that the connections between large-diameter pipes with wall thicknesses of up to 40 rom are of a high quality. Of all the possible welding processes, flash butt welding was chosen and a prototype machine developed to demonstrate its suitability.

The following is a report on the findings and results of numerous destructive tests which were carried outon the girth welds.

2. Pipelaying Method

As the welding process developed is for flash butt welding large-diameter pipes specifically for J-method pipelaying, it is appropriate that this new pipelaying system be summarized.

In contrast to the usual method of laying a pipestring in the form of an "S" from lay barges using long stingers, the pipestring laid by the J-method is paid out into the water through the middle of the pipelaying vessel by means of an inclined ramp, the angle of which is a function of the water depth (Fig. 1).

The depth to which the J-method can be used is limited by the axial loads resulting from tension and bending in the J-curve and also by radial stress resulting from the effect of the water pressure on the pipe. Dynamic loading and oncoming flow also have to be allowed for.
Novel Underwater Strengthening System For Tubular Joints
Authors: Tebbett Ian E. , Robertson Donald A.
Published: October 2008

This paper describes the novel use of a cement grouted sleeve as a means of strengthening tubular joints on a southern North Sea gas production platform to provide additional punching shear capacity. Two joints of X configuration at the -15 m (50 ft) level consisting of 610 mm (24 in) diameter members have been provided with split steel sleeve and cement grouthas been injected into the void between the sleeve and original structure.

This strengthening system was chosen as an alternative to a fully welded repair or mechanical clamping devLces the main advantages being reduced diving requirements, simplification of underwater habitats and the ability to accommodate fabrication tolerances, lack of fit and member distortions and misalignment.

As present design codes provide information on the strength of or design method for such systems, a programme of laboratory tests, including simulation of installation procedures, was undertaken to demonstrate the validity of the design. Details of the tests and results are presented together with details of the chosen solution and notes on the field installation. Of particular interest is the use of underwater welding methods to provide mechanical shear connectors on existing tubulars. This allowed the use of significant ly shorter sleeves and greatly simplified their installation.

Introduction

Cement grouted sleeves have previously been used only as a means of strengthening, connecting and repairing simple tubular members in a jacket structure. This paper describes a case history in which grouted sleeves have been used as a means of strengthening tubular joints.

The application described concerns two X-joints on platform AR of the southern North Sea Viking Field gas complex. These joints had been shown by reanalysis of the structure to have an inadequate safety factor against punching shear failure.

A grouted sleeve solution was chosen in preference to other methods (e.g welding or mechanical clamps) for reasons identified in the paper. The strengthening system was successfully installed during 1980 and thissuccess has established such systems as viable strengthening and repair alternatives for tubular joints.

Background

The Viking Gas Field is situated in Blocks 49/12 and 49/17 of the southern North Sea. The field consists of two manned platform complexes and five unmann ed satellite platforms. The five original 'A' and 'B' Complex platforms were installed in the period 1970 to 1972, the compression platforms, AC and BC, and the satellite platforms were installed in 1974/1975.

The 'A' Complex consists of five platforms of various sizes and leg configurations, interlinked by bridges. Platform AR which is of particular interesthere is situated at the west end of the complex and is the only six legged platform in the Viking Field. It serves as the main riser platform for the field and also provides accommodation for 30 personnel.
The Continuing Evolution Of Satellite-Based Geodetic Positioning And Survey Navigation Capabilities
Authors: Stansell Thomas A.
Published: October 2008

Introduction

Use of the TRANSIT Navigation Satellite System for offshore oil exploration and for land geodetic survey began in 1968. (To realize that we are well into the second decade of using this space-age technology for commercial applications was a slight shockto this author.) Many of the advances made in the state-of-the-art have been reported at previous Offshore Technology Conferences (see references 1, 2, 3, and 10). The purpose of this paper is to review the progress made since the previous reports and to examine trends affecting future developments.

This report covers three major areas. The first is the field of land geodetic survey in which three developments are reported. First is a multi-station network adjustment program called MAGNET. The second is a field translocation capability which has been implemented within the MX 1502 Satellite Surveyor instrument. The third development is a real-time translocation capability based on a communications link between two or more MX 1502 instruments.

The second area of this report focuses on the evolution of integrated navigation systems for offshore oil exploration. The objective is to show how these systems have matured since they were first described in references 1, 2, and 3. Also, trends affecting the direction of future developments are discussed.

Finally, this report evaluates the coming impact of NAVSTAR, the Global Positioning System. The future potential when the full satellite constellation is provided, the present potential with the interim six-satellite constellation, and concerns of the civil user community are discussed.

Geodetic Positioning

Background

One very important application of the TRANSIT Navigation Satellite System is for fixed point survey. In contract with satellite position fixes taken on a moving vessel, in which each position fix is used independently to update the dead-reckoned position, fixed point survey requires data from multiple satellite passes at a single location. With appropriate processing techniques such data can be used to obtain excellent survey results, thus avoiding the land traverse required with conventional survey techniques in which distance and angle measurements must be made from one point to the next, regardless of the intervening terrain.

Multiple pass satellite data can be processed in either of two ways: point positioning or translocation. In point positioning, data from a single receiver is used to obtain the .latitude, longitude, and altitude of its antenna. The only reference datum for this process is the satellite systemitself, and from 10 to 50 satellite passes normally are employed when operating in the point pos1tioning mode. A horizontal positioning repeatability of five meters rms can be expected with 25 satellite passes.

A variation on the point positioning technique is to employ a "precise ephemeris" rather than the orbit parameters obtained from the satellites themselves.
Natural Barrier Island Migration and Change - No Name Island, Beaufort Sea, Alaska
Authors: Gadd Peter E. , Gibson Dan H. , Nagel Robert H. , Sonu ChouIe J.
Published: October 2008

In March, 1981, Amoco Production Company constructed an exploration drilling pad on No Name Island, a natural barrier island located 14 miles northeast of Prudhoe Bay in the Alaskan Beaufort Sea. A monitoring program was initiated at No Name Island to determine the nature and extent of island change in response to the natural environmental forces active at the site. Two field surveys were conducted during the 1981 open-water season, the first in July and the second in September. Additionally, historical survey records and aerial photographs were investigated to determine long-term processes of island change.

The most significant changes observed between July and September, 1981, include island migration, island coalescence, and shoreline fluctuation. Although partially sheltered on its northern side by Cross Island, No Name Island exhibited changes similar to those observed on other Arctic barrier islands having more exposed locations.

At least two episodes of island breaching occurred between 1979 and 1981. The largest breach occurred near the northern end of the island and measured 300 feet in width. A smaller breach near the island midpoint has partially healed as a result of filling by littoral drift.

Between 1979 and 1981, No Name Island migrated southward at an average rate of 75 feet/year. On a long-term basis, the southward migration between 1949 and 1980 averaged 60 feet/year. The net littoral drift accounting for the observed long-term rate of migration is estimated to be approximately 50,000 cubic yards/ year.

Shoreline fluctuations adjacent to the drilling pad between July and September, 1981, measured 10 to 15 feet on both the east and west shores. These fluctuations were accommodated within the 30-foot wide beach-front margin which was specifically avoided as a site for the drilling pad foundation due to its unstable nature.

The recent history of No Name Island indicates the potential for dramatic short-term changes in both island shape and location. Cognizance of the major natural processes at work, provided by the monitoring program, will promote the proper design of future operations on the island while preserving the integrity of the island's natural environment.

Introduction

During the early months of 1981, Amoco Production Company constructed a drilling pad on No Name Island, a barrier island located approximately 14 miles northeast of Prudhoe Bay, Beaufort Sea, Alaska (Figure 1). No Name Island constitutes the southern component of the accurate Cross Island barrier complex and, unlike most of the barrier islands in this region, is oriented in an approximate north-south direction. Over the 4000 foot length of the island, the island profile varies from a minimum elevation of less than one foot and a minimum width of 20 feet at its northern extremity, to a maximum height of approximately five feet (above mean sea level) and a maximum width of 350 feet near its southern shore.
Wave Prediction in Shallow Water
Authors: Resio Donald T.
Published: October 2008

Introduction

Considerable research has been concentrated on deep-water prediction in recent years. This has led to the development of rather sophisticated wave prediction schemes which have been tested successfully in field experiments under a variety of conditions. However, progress in deep-water wave prediction has not been followed by commeasurate advances in shallow water wave prediction. Since many offshore structures are located in relatively shallow water, this inability to obtain accurate predictions can have large economic consequences.

There are two types of shallow water wave-prediction which this paper intends to address. First, there is the situation in which the entire generation area lies in relatively shallow water. Second, there is the situation in which waves are generated in deep water can be integrated over all propagation directions and then propagate into shallow water. The first situation can be important in selected areas such as semi-enclosed basins, shallow bays or regions where ice cover can restrict the fetch area to a shallow region along the coast. The latter situation is important in coastal area all around the world, where large storm waves oropagate from deep water in to the coast.

The theory presently used by most engineers in estimating shallow water wave heights is based on published charts in the Shore Protection Manual (1973). Basically, the concept behind this theory follows from a theoretical treatment of direct atmospheric input into a monochromatic wave train with a simultaneous solution for the rate of energy loss due to bottom friction (Bretschneider and Reid, 1953). It is well known that the bottom friction factor is highly sensitive to bottom materials. Since the energy flux into the wave field from the atmosphere should be somewhat independent of bottom materials, this theory suggests that the predicted wave heights should be highly dependent on the bottom conditions. The published graphs in the Shore Protection Manual are specifically for a bottom friction factor 0.Ol.

Theoretical Treatment Of Wave Generation In Shallow Water

For surface gravity waves in a constant depth of water, the rate of change of a two-dimensional wave spectrum can be written asEquation (1) (Available in full paper) where E2 (f, ?) is the two-dimensional frequency direction spectrum, S2(f, ?)) is the net energy flux into (or out of) a spectral component, v is the group velocity vector and v is a horizontal gradient operator .In simple, idealized situations, equation 1 can be integrated over all propagation directions to obtain a representation of the rate of change - of the one-dimensional spectrum (Hasselmann et al., 1976).Equation (2) (Available in full paper) where x is the mean propagation direction and v xis the average group velocity along the x-axis and S1 E1 are the forms for S2 and E2 integrated around the propagation direction ?.

Hasselmann (1962) developed a theory for nonlinear wave-wave interactions which predicts a transfer of energy among various components in a spectrum.