bluuebunny/crossref_metadata_2025_split huggingface dataset:
MIG-Welding of Offshore Steels at Pressures From 1 to 30 Bar
Authors: Terlinde G.T. , Mueller L.G. , Schwalbe K.H. , Beaven P.A. , Szelagowski Peter 
Published: October 2008

ABSTRACT
Hyperbaric welding was performed in an unmanned chamber at pressures up to 30 bar (300 m depth). A flux-cored and a solid wire were used as consumables; two typical offshore steels served as base materials. The study, which mainly focussed on the weld metal properties, included chemical analysis, detailed microstructural characterization, tensile and charpy impact testing, and for selected conditions a fracture mechanics analysis. When using argon as pressurizing gas, the impact toughness decreases only slightly at higher pressures «15%); the room temperature tensile properties and COD values for crack growth initiation show no pressure dependence. The solid wire has slightly lower impact toughness values than the flux-cored wire. An attempt is made to explain the mechanical properties on the basis of the observed microstructures.

INTRODUCTION
For more than a decade extensive efforts have been made in the development and application of underwater welding /1–11/. This is mainly due to the repair and construction work which has to be carried out on underwater parts of pipelines or platforms installed by the offshore industry /12–14/. Various methods are used depending on the water depth and the type of work; recent results have been summarized in numerous reports eg /2,3,5/. Underwater wet welding, for example, is characterized by the welder being in the water and the weld region being either wet or covered by a small gas filled chamber. Dry, or hyperbaric, welding is performed with the welder and the weld area in a gas filled chamber, which is held at the pressure of the surrounding water. In addition, 1 bar.
Welding is possible by keeping the pressure in such a chamber at 1 bar. There are two important factors which complicate underwater welding, namely the pressure and - especially for wet welding the water. These can, for example, cause changes in the arc geometry, temperature and stability /2,3,15/, variations in the metallurgical reactions /1–6,12,16,17/, strong effects on the cooling times /4-7,9–11/, and increased hydrogen concentrations in the weld /13/. Although code quality underwater welding is possible today to a limited extent, in most of the studies a loss of toughness has been observed with increasing water depth /1,4,5/; a complete understanding of this embitterment has not yet been achieved.
The GKSS research center has started an extensive marine technology program, which includes underwater welding and which is focussed on both technological development and more fundamental research. As part of this underwater program, a series of tests with dry hyperbaric MIG welding will be described in this paper. The tests were carried out at pressures from 1 bar to 30 bar. The materials selected were a pipeline steel StE 445.7TM (=X65TM), and a structural steel StE36 (500) which is used for platform components. Based on preliminary tests two commercial C-Mn-Si wires, one a flux-cored wire with basic flux, and, the other a solid wire, were chosen.
Dynamic Positioning in Single-Point Moorings
Authors: Sørheim Hans Roar , Gregersen Steinar Roar , Jenssen N.A. 
Published: October 2008

ABSTRACT
This paper deals with the concept of and a system for complete control of the slowly varying bow motion of a bow-moored ship using dynamic positioning.
System performance is shown by simulated case studies with an offshore 1oading tanker. Significant improvements of motion behaviour and mooring force performance are demonstrated. A complete positioning system is presently runn1ng successfully onboard a 125000 dwt tanker in the North Sea. Some preliminary results are shown.

INTRODUCTION
Mooring of large ships at offshore terminals are done by single-point mooring. The ship is connected to the terminal through a single mooring line, or hawser, which allows H to position itself according to the preventing weather and sea conditions, like a weather-vane, and thereby to remain moored with a minimum mooring force when the direction of forces changes.
A major problem faced by single-p01nt mooring In hostel areas is due to the motion of the ship and the terminal. The ship tends to oscillate slowly relative to its mooring point with a following oscillatory behaviour of the mooring stresses, and with the effects of wave following motions superimposed. When the mooring force exceeds a prescribed value, loading must be stopped and mooring abandoned. The low frequency ship motionstems from unstable ship mooring configuration and/or dynamic force excitations from wind and wavesl.
From practical experience a certain amount of astern thrust is found to have a favorable effect on the slow motion, but it is questionable as a remedy for reducing peak hawser tension.
Dynamic positioning (dp) has been applied with great success to freely moving ships and moored vessels for more than ten years. While keeping the ship In a fixed position is typical to most dp system applications, the desirable objective in single-point mooring is to keep the distance between the mooring terminal and the ship's bow as nearly constant as possible, while maintaining the overall weather-vane capability.
In this paper a review of the essential slow motion behaviour of a bow moored tanker 1s presented with emphasis on stability and mode dynam1cs. The des1gn and the theoretical performance of a dp-system to meet the single-point mooring positioning objective Is presented and, finally, results from full scale tests with a 125000 dwt tanker during offshore loading are shown.

ANALYSIS OF SLOW MOTIONS IN SINGLE-POINT MOORING
Only static (elastic) properties of the mooring terminal affects the slow motion behaviour, while the high frequency (wave following) propert1es are reflected in the mooring force. Hence, the terminal is left out in the following analysis.

Governing equations
The governing equations describing the slow motion of a bow moored ship In wind, waves and current are reasonably well establ1shed. A detailed description is presented In1.
Applying some symmetry assumptions, the equations of motion In moored ship coordinates.
Model Tests With a Single-Point Mooring System In ShortCrested Waves
Authors: Høulie Morten , Stansberg C.T. , Werenskiold Per 
Published: October 2008

ABSTRACT
Laboratory experiments with a deep-water singlepoint moored tanker model in irregular waves are reported. A rigid mooring arm is used. Wave induced forces and motions in both long-crested and short-crested sea are investigated. Short-crested waves are usually believed to decrease the wave loadings. In many cases this is not necessarily the case. The aim of the present paper is to point out possible significant differences between wave loadings of short-crested and long crested waves.

INTRODUCTION
The oil industry is applying floating production system in increasing numbers for the development of off shore fields. There are a number of floating production schemes currently in use or under design, which use a floating surface support vessel. The most important factor in successful design of any production riser concepts is thorough knowledge of the environmental conditions and the loads they apply to the structure. Both for determining design and operational ability, it is important to know whether or not short-crested sea should be taken into account. The results and conclusions from this paper are primarily useful when working with single point mooring problems. The magnitude of differences in responses in short-crested and long-crested waves indicate that the results will be of interest in analysis of non-rigid systems in general.
In this paper we are going to describe tests which were conducted in both long-crested seas, with and with out wind at various heading angles, and in short-crested seas. In this paper, special emphasis is given to compare results from unidirectional head seas and multidirectional seas. These tests were a part of an extensive model test program carried out in order to investigate a deep water SALMRA (single anchor leg mooring rigid arm) moored storage tanker system. The tested SALMRA system is a double articulated system design for 375 m water depth and for North Sea conditions. Main features of the system are a gravity base, a structural riser, a large top buoy to provide the restoring capacity and a rigid arm of the truss type for permanent tanker mooring. Fig. 1 shows the system in general.

EXPERIMENTAL SET-UP

Ocean basin
The model experiments were carried out at the Norwegian Hydrodynamic Laboratories (NHL) ocean basin. Fig. 2 shows a plan view of the Ocean Basin and the towing tank. Further, a cross-section of the Ocean Basin and some characteristic data are shown.
In the basin, two different wave generators are installed. In one end a hydraulically driven double flap generator is located, which is able to generate unidirectional waves with a maximum wave height of 90 cm referring to regular waves. A beach is located in the other end of the basin.
At one of the sides of the basin, a 62.5 m long wave generator is located. It consists of 144 individually controlled flaps which are able to generate unidirectional or multidirectional waves.
Shallow Seismic-Derived Acoustic Core Logs
Authors: Caulfield D.D. 
Published: October 2008

ABSTRACT
A small micro-computer system with analog-to-digital sampling intervals to 30 microseconds has been developed for field processing of shallow seismic data. This digitizing capability plus an absorption model for marine sediments has allowed the development of a system for predicting acoustic impedance versus travel time.
Utilizing regional data tables for soil type versus acoustic impedance and absorption such as Hamilton and Bachman has allowed for the actual prediction of soil type, density, and grain size as a function of depth. The prediction accuracy is closely related to the signal-to-noise (S/N) of the received data, while the depth of penetration and resolution is related to the seismic frequencies employed.
The model is discussed in detail with two years of data examples versus actual core data from the Beaufort Sea and Vancouver offshore areas given for review. Application areas such as dredging, pipeline surveys, and material location for offshore construction are discussed. In addition, limitations and further signal processing requirements are reviewed.

INTRODUCTION
Caulfield, et. al.1,2 introduced concepts for the extension of Hamilton's reflection modeling into the prediction of sub-bottom material types through correction of signal levels by simplified absorption and other correction models. This paper discusses a number of system improvements and summarizes practical applications to data acquisition in the Beaufort Sea and the Vancouver Harbour regions.
The major improvements have been achieved by the application of standard deep seismic techniques to high frequency digital analysis problems. These improvements are summarized as follows:Signal-to-noise (S/N): The S/N is calculated before any corrections are made to the data. Only reflections that have a S/N greater than 5 db are considered as valid data points. This has improved prediction accuracy by at least 5 percent.Travel Time Layer Identification: A simple algorithm is used to calculate the exact travel time. The first reflection is taken as an image of the transmitted signal, and subsequent traces are cross-correlated to this to determine the exact position of the layer. Obviously, accurate travel times can be determined for layers of good S/N.Iterative Solutions: Beginning with approximate densities for the region from calibration cores combined with accurate travel time information a first solution is calculated. New density values and velocity adjusted travel times can then be applied to successive iterations. Iteration ceases when the error difference between the output of the derived synthetic model and the observed input signal amplitudes has been minimized.
The entire program has been aimed to develop systems that are practical to aid in field interpretation of data and or laboratory processing at minimum cost. Some of the above algorithms require extensive processing times which could be improved with parallel processors, etc. As is evident from the identity(Mathematical equation available in full paper)
Ice/Berm Interaction Study Using Rotary Sidescan Sonar and Acoustic Profiling Systems
Authors: Good R.R. , Anderson K.G. , Lanziner H.H. 
Published: October 2008

ABSTRACT
Tarsiut Island, in the Canadian Beaufort Sea, was the first dredged caisson retained island built for exploration drilling operations in the Arctic offshore. Due to the island is configuration location, a large first-year ice rubble pile would result from the ice/structure interaction. This paper outlines how a rotary side-scan sonar and a mechanically scanning, narrow-beam acoustic profiling system were used to determine the geometry and the contact area of the underside of heavily rubbled first-year ice. The results of this study are to be used to further the understanding of the nature and mechanism of the ice/structure interaction in Arctic offshore structures.
The sonar transducers were deployed through augered holes in the ice thus permitting horizontal rotation. The systems were also configurated to allow an indirect remote means of data acquisition of the underside of the ice as well as the beam/seabed surrounding the caisson retained island.
Of main interest, was the geometry of the deep draft grounded ice at the edge of the ice rubble annulus, knowing the geometry and the contact area of the grounded rubble was required for use in understanding the ice load transfer mechanism between the rubble field and the island beam. Thirty-six under-ice profiles were taken from each of 14 locations in conjunction with a 360 degree side-scan sonograph acquired from each hole so as to encompass the circumference of the island. Aerial photographs were used to provide the above water geometry of the rubble field.
Sonar profiles were ground truthed utilizing manually drilled holes to establish the level of accuracy, and to allow necessary calibration corrections. The combination of these two systems utilizing remote indirect methods in this unique application provided Gulf Canada Resources Inc. and the participants in APOA Project No. 198 with both cost effective, quantative and qualitive engineering data.
The definitive resolution and detail of the data over such a large extent had not been previously attainable in so little time.

INTRODUCTION
To ensure safe stable platforms for offshore exploration, artificial islands are commonly being wilt in the Beaufort Sea. Two main types of artificial islands have beenused to date; sand with long-sloped beaches, in up to 20 m of water, and sand-supported steel or concrete caissons.
Tarsiut is a caisson retained island on a sand beam designed to reduce the quantities of fill required and the time needed for construction.
Although many artificial islands have been wilt in the Canadian Beaufort Sea (Figure 1), the Tarsiut structure represented a significant new extension to the Arctic drilling technology. The island (Figure 2) was designed and constructed under contract to Gulf Canada Resources Inc. by Canadian Marine Drilling Ltd., and was the first caisson retained island used for exploratory drilling in ice-infested waters (Fitzpatrick and Stenning, 1983)3.
Full-Scale Measurement Tests on the New Semisubmersible Polycastle
Authors: Tamaki I. , Sødal F. , Takanashi S. , Nakayama K. , Inui T. , Kobayashi M. , Nakamura K. 
Published: October 2008

ABSTRACT
Full scale measurements onboard the newly built semi-submersible unit POLYCASTLE were carried out in the North Sea in February and March 1983.
The objective is to discuss the measured results of motion and stress by comparison with the design estimates through computer calculations and model experiments.
It is said in conclusion that the design efforts of the POLYCASTLE have been well appraised both in operation and safety points of view.

INTRODUCTION
A great number of semi-submersible units has been recently put in operation by offshore industries. But recent incidents in the past years have given rise to concern about the safety of semi-submersible units.
After the disaster of the A. L. Kielland, March 1980, the Norwegian authorities and others have renewed their rules and requirements introducing the thought of safety by redunduncy.
The initial design of the POLYCASTLE commenced enthusiastically in May 1980 to apply the new rules and requirements, and she was delivered to the Rasmussen Offshore A/S early in 1982. Her maiden operation in the North Sea began in July 1982.
In the circumstances described above, full scale measurements onboard had been advocated to estimate the design efforts.
The measurements were carried out in February and March 1983 during the stormy season at the Magnus Field of the North Sea, and were concentrated on the incident wave to the unit, motions of six degrees of freedom and stresses acting on the structural members of the horizontal and transverse diagonal bracings. Each measurement took 30 minutes four times a day. The measurements were carried out 87 times (22 days)
(PRINCIPAL PARTICULARS) (Available in full paper)

MEASUREMENT INSTRUMENTATION
Incident waves were measured by a non-contact radio wave-type wave height meter, which was installed on the upper deck facing to the sea. (Fig. l) The meter indicates directly the relative oscillation of the water surface; the vertical displacement of the unit was eliminated by doubly integrating the vertical acceleration simultaneously measured by the accelerometer.
Pitching, rolling, and yawing motions were measured by the gyroscopes, and swaying, surging and heaving by the accelerometers.
As shown in Fig. 1, stresses at the horizontal and transverse-diagonal bracings were measured by the strain gauges which were sealed hermetically with a rubber compound. The sealed wire codes were used to reduce the noise level.
Other environmental factors were also measured: wind by the anemometer (measured at 42 meters above sea level), current by the propeller type current meter, and wave direction by observation, etc.
The Use of Vertical Seismic Profiling in Geotechnical Site Investigation
Authors: Justice J.H. , Hinds R. , Stirbys A.F. 
Published: October 2008

ABSTRACT
Field experiments carried out in the Beaufort Sea in 1983 indicate that the vertical seismic profile (VSP) has potential as a valuable tool for determining geotechnical material properties required in site surveys preparatory to construction or drilling. If both shear and compressional waves as well as density can be obtained from borehole surveys, then elastic moduli of interest can be inferred. Experience shows that the potential and economics of this type of survey are good. However, more work should be done to identify reliable sources of shear waves in order to obtain a full interpretation of the elastic moduli of interest in near-surface material.

INTRODUCTION
Several of Canada's major oil companies are actively exp1oring the oil resource potentia1 of the continental shelf of the Canadian Beaufort Sea. Gulf Canada Resources Inc. (GCRI) is an exploration operator in this region (Figure 1).
At potential exploration drilling sites, complete and accurate geophysical and geotechnical evaluations of the upper 100 m of bottom sediments are required to:assess the stability of gravity base structures and artificial islands under large horizontal ice loads during year-round operations.estimate the available holding power of the mooring system of floating drilling units.identify any shallow drilling hazards such as shallow gas, permafrost and gas hydrates.identify potential borrow material. Present site testing techniques include:high resolution shallow seismic mapping over a 5 sq. km area on an approximate 250 m to 500 m grid pattern to give a three dimensional image of site stratigraphy complemented bygeotechnical sampled boreholes and in-situ tests to obtain detailed engineering parameters and stratigraphy of a specific foundation site. Vertical seismic profiles (VSP) were introduced into the geotechnical program in 1983 on a trial basis. Currently it is unusual to use this method in the geotechnical context offshore. The purpose of the VSP was:to provide a link between seismic and geotechnical data,to provide some conventional geotechnical parameters,to provide a continuous seismic log of an intermittently sampled borehole. This paper describes the VSP operations, presents some preliminary results and outlines some improvements that should be made in operational technique. It appears that the VSP has application as a routine procedure in any offshore geotechnical investigation.

DESCRIPTION AND THEORY OF VSP
The VSP is a method of measuring seismic wave velocity by timing a wave front between two points a known distance apart. The measurement is made between a point on or close to the seabed and a point in a borehole a known distance below the seabed. Measurement is made, therefore, on an approximately vertical ray path. Multiples, tube waves, etc., are allowed for in the interpretation.