bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Line And Transverse Forces On Cylinders Near A Wall In Oscillatory Flow At High Reynolds Numbers
Authors: Sarpkaya Turgut 
Published: October 2008

ABSTRACT
The in-line and transverse forces acting on circular cylinders placed near a plane boundary in a sinusoidally oscillating fluid in a U-shaped vertical water tunnel have been measured. The drag and inertia coefficients for the in-line force have been determined through the use of the Morison's equation. The transverse force has been expressed in terms of a single lift coefficient. The results have shown that the effect of wall-proximity is to increase the force coefficients for-relative gaps of e/D less than about 0.5. In this range of e/D values (0&lt;e/D?0.5) the non-linear interaction between the shear layers emanating from the top and bottom of the cylinder is reduced and the frequency of oscillations in the shear layers is a synchronised. For e/D larger than about 0.5, the regular vortex shedding resumes, more or less unimpeded by the presence of the wall, and the lift, drag and inertia coefficients nearly assume their free-cylinder values.

INTRODUCTION
There are numerous problems associated with the design and installation of pipelines in deepwater offshore. The results such as the ones presented herein touch upon only one facet of the submerged pipeline design and do not deal with the consequences of pipeline forces due to temperature, pressure, seabed friction, buckling, scour, hydroelastic oscillations, etc. Suffice it to say that the reliable design information is most likely to come from a combination of laboratory studies, field experience, and careful documentation of the causes of failures.
The present investigation is fn extension of that previously reported by this writer1 and was undertaken for the purpose of determining the in-line and transverse forces un cylinders near a wall at relatively higher Reynolds numbers.
It is a well-known fact that for very small values of the period parameter UmT/D, the flow about the cylinder does not separate, the wake-dependent drag force is very small or negligible and the in-line as well as the transverse forces are essentially from the wave temporal acceleration. Under such circumstances, the appropriate coefficients may be easily evaluated from the potential theory. When the cylinder touches the boundary, a net force exists away from the wall. However, if even a very small gap exists between the cylinder and the wall, then a large net force exists toward the wall. The inertial forces alone do not usually give rise to the maximum load situation for small structures, such as pipelines located on or near ocean bottom, and the separation effects become extremely important not only in the determination of the magnitude but also the direction of the forces.
It is important to recognize that the separation effects are not free from the effects of the boundary layer which forms on the bottom plane.
Dynamic Response Of Agravity Platform Under Random Wave Forces
Authors: Nataraja R. , Kirk C.L. 
Published: October 2008

ABSTRACT
A spectral analysis of a typical multi-tower gravity platform is carried out considering soil-structure interaction. The modal frequency response function and the linear hydrodynamic load transfer functions are determined taking into account diffraction effects. The displacement and wave loading spectra are evaluated for sea states described by the JONSWAP wave height spectrum relevant to the North Sea environment. Considerable simplification is achieved by a reduced interaction model together with complex notation for wave forces. A detailed parametric study using various values of soil shear modulus yields r.m.s. values of deck displacement and tower elastic deformation.

1. INTRODUCTION
With the increase in the rate of world oil consumption, exploration and production has moved into deeper and environmentally more hostile waters. The first phase of this development favoured fixed platform with concrete gravity structures being designed for water depths up to 150m and the steel jacket for water depths up to 300m. The first concrete gravity platform, Ekofisk I, was installed in the North Sea in June 1973 and by the end of 1977 there will be more than 12 concrete platforms in operation. These are generally of a multi-tower (2, 3 or 4 towers) configuration with a large base caisson of cellular construction extending up to 1/3 of the height of the platform, or a manifold type of construction with a large diameter base raft up to 150m in diameter.
In designing a gravity platform it is necessary to consider the effect of wave forces on both the towers and the caisson in order to calculate the structural and foundation stresses. A detailed analysis of a rigid four tower gravity platform supported on a rigid foundation under deterministic and random wave forces is given by the authors in ref l.
The present paper gives a random dynamic analysis of a typical multi-tower gravity platform (Condeep Brent 'B') taking into account flexibility and damping of the towers and of the foundation The random wave forces are calculated for a fully developed sea state represented by the J.O.N.S.W.A.P. wave height spectrum11, which is typical of the North Sea. Due to the relatively large diameter of the towers hydrodynamic drag forces are small compared with the inertial forces on the towers and the diffraction forces on the caisson and can be neglected, enabling a linear spectral analysis to be used. The fluid inertia loading on the towers is evaluated using Morison's equation and diffraction theory where relevant. The wave forces and moments on the caisson are computed using the results of wave diffraction analysis2,10
The spectral analysis is carried out by formulating the wave force transfer function for unit wave height using complex notation, taking account of the phase differences of the waves due to spatial separation of the towers. The frequency response function is based on a real eigenvalue analysis through a modal formulation of the soil-structure dynamic model.
Deep Water Drilling From Amoored Semisubmersible
Authors: Kobus L.C.S. , Meyers H.M. , Bounds V.G. 
Published: October 2008

ABSTRACT
A new series of floating-drilling semi submersibles, the Zapata 55-2000 class, have been in operation fore total of 24 months. During that time, the first two rigs of the four rig series have drilled at twelve locations in the 900-l400 feet water depth range in the Gulf of Mexico. This paper describes the design features of these innovative semi submersibles and their unique deep water mooring systems. Operational techniques and problems peculiar to drilling in 1000 feet of water are discussed. This paper describes actual operating experience that can be of use in advancing normal floating drilling operational capabilities into deep water.

INTRODUCTION
When the BLUE WATER I was being redesigned and modified to serve as the pioneer semisubmersib1e drilling unit by a team of major oil company technical experts in 1959-1961, the 200-300 ft. water depth range was considered to be "deep water" for floating drilling operations. (Figure 1)
That historic "sit-on-bottom" submersible, which was redesigned and modified to operate in a"semi"-submersib1e or floating mode, was the forerunner of the semisubmersib1e offshore drilling rig. After the concept of drilling while floating on a Semi submersible "Island of Steel" was proven by the BLUE WATER I project to he technically, operationally and economically feasible, a whole new class of offshore drilling rigs came into existence. The first new semisubmersib1e to be designed and built was the innovative eve-formed once OCEAN DRILLER in 1963. Since that time, 123 more semi submersibles have been constructed and put into operation.
Zapata's design efforts in the late 1960's and early 1970's were directed towards the development of a super class pf semi submersibles, with capabilities to operate safely and effectively in the harsh environments of the North Sea, the Gulf of Alaska and the stormy regions of the extreme southern latitudes of the Atlantic, Pacific and Indian Oceans off the Antarctic continent. The Zapata 55-3000 design class and the ZAPATA UGLAND were the resultant products of that design effort.
However, in 1972, Zapata set its sights on the development of a lesser capability class of semi submersibles that would be more suited and could safely, effectively and economically operate in deep water (1000-2000 ft.) on the continental shelf and slope areas off the Eastern, Southern and Western coasts of the United States and as well as the Eastern and Western coasts of Canada.
Evaluative study efforts resulted in Zapata teaming with the noted design consultants, Frieda and Goldman, in 1973, to modifying one of their standard designs to suit Zapata's specific design requirements. The product of that joint-design effort between Zapata and Frieda and Goldman is the Zapata SS-2000 class - the ZAPATA CONCORD (1975), ZAPATA LEXINGTON (1976), the ZAPATA SAPATOGK (1976) and the ZAPATA YORKTOWN (1976). (See Figures 2,3,4 and 5).
Challenges Associated With The Design Of Oil-Gas Separation Systems For North Sea Platforms
Authors: Penick Dudley P. , Thrasher William B. 
Published: October 2008

ABSTRACT
The conditions encountered in North Sea oil-gas separation facilities design and operations require that the system be both highly selective and extremely flexible within the space and weight limitations of a production platform. To better understand the approaches used by process engineers in attempting to solve these difficult and sometimes conflicting challenges, this paper discusses the objectives, some of the more significant factors which influence the potential solutions to these objectives, and some of the approaches utilized to meet these challenges.

OBJECTIVES

1. Produce Specification Crude Oil
Crude oil specifications may be either for offshore tanker loading or for delivery to an oil pipeline at the platform. Crude oil specifications are usually defined relatively simply, through limitations on vapor pressure and on BS&W (basic sediment and water) content. BS&W is normally limited to a nominal percentage, such as 0.5%, and meeting this specification is outside the scope of this paper. The oil-gas separation system in most cases? does not significantly affect whether or not the oil will meet the BS&W specification, since for those oils where this is a problem special emulsion treating is required independent of the oil-gas separation system.
Crude oil vapor pressure is the specification which most influences the design of oil-gas separation systems. For offshore tanker loading, the oil may be limited to a vapor pressure in the range of 8 to 14 pounds RVP (Reid Vapor Pressure). RVP refers to a standard method of vapor pressure testing utilizing a specific test cylinder assembly and determined at a temperature of 100°F. RVP is not identical with TVP (true vapor pressure), which is the actual vapor pressure exerted by a liquid in equilibrium with a vapor at any given temperature. Oil leaving an oil-gas separator operating at 15 psia and 1000F will have a TVP of 15 psi at 100°F. Because of the nature of the RVP test cylinder, TVP of a liquid at 100°F will always be slightly higher than RVP. The amount of this difference is a function of the liquid composition and can be estimated.
Crude oil vapor pressure limitations for pipeline delivery may be comparable to those for tanker loading. However, a pipeline can be specifically designed as a high vapor pressure system to handle gas liquids components mixed with the crude oil, and it is quite possible that North Sea oil pipeline systems will be developed in this manner .It is not expected to be feasible to recover NGL components separate from oil and gas on the offshore platforms and construct separate NGL pipeline systems. It also may not be possible in every field to design a separation system which meets both gas specifications and low crude oil vapor pressure specifications unless an intermediate product is also made. This will be more fully discussed later in this paper.
Prediction of Weather Downtime for Derrick Barges
Authors: Rawstron Philip J.M. , Blight Graham J. 
Published: October 2008

ABSTRACT
As oil is found in more hostile environments, economic and rapid completion of offshore production facilities will depend more heavily on the sea keeping ability of construction vessels. However, the relationship between vessel motion characteristics and the percentage of time that the vessel will be able to work is not generally understood.
The net effect of the vessel motions on lifting operations can be reduced, in fact, to a single value represented by the vertical motion of the crane boom tip (or sheave centerline). The explanation for this is quite simply that the corresponding vertical motion of the hook controls the ability to safely pick-up or set-down a load. This single assumption presupposes that the lateral or swinging motions of the load are not a direct function, but rather an indeterminate consequence, of the lateral or horizontal motions at the boom end. Thus, vertical hook or boom end motion can be used as a parameter to qualify the operational tenacity of a derrick barge.
Barge operation reports and corresponding measured wave data were analysed to yield sea-states when work could be accomplished. Further analyses provided the maximum vertical boom end motions with which piling work or module lifts could be carried out. These maximum vertical motions can now be used as criteria todeterm1ne the expected number of working days for a particular vessel at a given location, according to the operation required.
A computer program has been developed to carry out the process, which is described in the paper. The method is based on the vessel motion characteristics, statistics of the expected weather and limiting criteria of vertical motion. The paper discusses the influence that equipment aids, such as heave compensators and tag-line .systems, might have on the predictions. A comparison is shown of the expected performances of typical heavy lift vessels in the North Sea.

INTRODUCTION
Model tests have been used for many years to determine the sea keeping characteristics of floating vessels. More recently computer programs have been developed which will perform the same task with equal reliability, but less expensively and much more rapidly. However, it is not immediately obvious from the fundamental motion responses derived by either method as to how efficiently a proposed vessel will operate in practice. All that can be done, provisionally, is to compare the motions of the proposed vessel with those of existing vessels. This procedure is clearly insufficient, even if motions in corresponding sea-states are compared, because it fails to recognize the effect of variations between the arrangement or geometry of different vessels. It also completely ignores the practical factors of the operation to be performed by the vessels.
For a derrick vessel the ability to work is primarily a function of the relative motions between the package being lifted and the foundation on which it is to be set down. The ability to work can also be controlled by relative motions at the time a package is to be picked up.
Self-Installed Deck On Offshore Platform
Authors: Orfali M. , Herve J.L. , Buzzichelli M. 
Published: October 2008

ABSTRACT
This paper attempts to describe the development of "self-installed" decks on offshore platforms.
When North Sea operations first started platform installation was performed by means of conventional derrick barges i however, faced with harsh sea conditions, they did not prove very cost effective and installation was often delayed.
Thus, operators were driven to seek new concepts. Among them, TOTAL CFP, operator on the Frigg pipeline, chose to erect big cranes on bare platforms in order to complete installation. This concept soon proved to be a reliable one as it became far easier to take advantage of narrow windows of good weather than it would have been possible with derrick barges. Moreover, safety was increased.
After a few modifications, this installation scheme can be applied to a wide range of fixed platforms both in rough and calm seas.
In this paper, our intention is to explain why we chose this concept and to give the main results gained from our experience on the field.

INTRODUCTION
Within the scope of the Frigg operations, TOTAL, as operator on the pipeline developed several completely new techniques which involved the installation of lifting devices with a load capacity of 300 t to 800 t on platforms.
Once developed by TOTAL and BUZZICHELLI, these techniques enabled offshore lifting operations to be carried out rapidly in weather conditions which were unsuitable for conventional lifting devices.

APPROACH TO THE NEW CONCEPT

North Sea beginnings
When operations first started in the North Sea, production platforms were equipped by means of conventional derrick barges.
The latter can work in up to half a foot heave but roll is critical, the limitation being between 0.5 and 1° depending on the size of the load. In the North Sea, these thresholds are often over-reached resulting in long waiting for calmer weather and sometimes in postponements of operations for up to 8 months, should they not have been completed before the winter season.
Moreover, safety is sometimes affected. Indeed, once a package has been lifted a cargo barge becomes very lively, which lead to a very tricky situation, as it is impossible to drop the package down either on the platform or back on the cargo barge. Should by any chance, the load then start swinging laterally, it is almost impossible to control.
Big modules and huge barges : some improvement but many disadvantages.
In an attempt to improve North Sea operations huge derrick barges appeared. They could handle large and heavy packages (up to 2 000 tons) in slightly worse sea conditions.
It was agreed that the bigger the modules, the fewer lifts required to install them. This was in fact quite true, but several disadvantages should be pointed out.
Dynamic Response Of Flexible Offshore Structures To Regular Waves
Authors: Taudin p. 
Published: October 2008

ABSTRACT
The highly nonlinear fluid solid interaction can be studied by an iterative calculation procedure described in the paper. It is a convenient method for the computation of the steady response of tubular structures.
An extension of the method is possible so as to obtain response curves through the wave periods. They describe the behavior of the structure in various sea conditions, from small and short waves to high and long ones.
The response curves can be used to calculate the spectral response to a sea spectrum if the structure is not highly nonlinear.

INTRODUCTION
An offshore structure is said to be flexible when the displacements, speed, and accelerations of the structures elements highly affect the wave and buoyancy forces. According to such a definition, a same structure can be flexible only for some sea states and rigid for others. A typical property of flexible structures is that the relation between the hydrodynamic forces on the motionless structure and the displacements is nonlinear.
Our purpose is to study flexible structures built with tubes, using the Morison's equation for the calculation of wave forces and to propose a low-cost iteration procedure for the calculation of the steady response to a large variety of wave periods and wave heights.
An objection to such a study may be that the theory of regular and cylindrical wave3 is not realistic. But we think that the large amount of information given by the iterative procedure about the behaviors will be helpful in the nonlinear spectral analysis (this is the theme of our present research).
On the other hand, we have noticed that the regular response is of a high practical interest. Thanks to the method presented hereafter, it has been possible to calculate what wave periods are the most dangerous for a structure, for a given wave height. It, has been possible to delimit in the H,T plane, the curves of equal fatigue duration, then to determine the towing feasibility of structures.

EQUATIONS OF MOTION

Basic Hypothesis and Simplifications

Structure Schematization
The structure is composed of tubular beams whose length and diameter are small, when composed to the wave length. Each beam can be cut artificially into small elements along which any function of space will be taken as constant. Then the structure will be represented only by a set of points corresponding to the center of gravity of the elements. Each of the following properties are defined for each point.
(Available in full paper)

Base of Displacement Fields
A set of n arbitrary vector functions of space are chosen:
(Mathematical equation available in full paper)
They represent a base of displacement for the structure. It is supposed that any displacement of a tubular element is represented by the formula.
Submarine Landslides In The Mississippi River Delta
Authors: Coleman James M. , Prior David B. , Garrison Louis E. 
Published: October 2008

ABSTRACT
Systematic side-scan sonar and high-resolution seismic records from the shallow-water offshore areas of the Mississippi Delta have revealed widespread sub aqueous slope failures in bottom sediments. These failures have resulted in damage and loss to offshore structures and pipelines. The features occur on slopes with very low inclinations (ranging from 0.2° to 1.5°) and in water depths of 5-100 m. The types of features include collapse depressions, bottleneck slides, elongate slides and slumps, mudflow gullies, and overlapping mudflow lobes. Although movements include both vertical and rotational displacements, the bas1c mechanism can be approximated as down slope translation of shallow slabs of debris. Although movement rates of up to several hundred meters/year have been documented, it is postulated that large-magnitude surged may be inherent in these features. These submar1ne landslides result from complex temporal and spatial combinations of wave-induced stresses, sediment loading, and generation of high pore water and methane gas pressures.

INTRODUCTION
Numerous detailed marine surveys (high-resolution geophysical, side-scan sonar, and bathymetric data) have been conducted in the area offshore of the Mississippi River. These surveys have revealed the presence of a large number of distinct types of sub aqueous slope instabilities that can be generally classed as submarine landslides. Most of these bottom sediment mass movements are of sufficient magnitude to severely endanger bottom-emplaced petroleum facilities such as offshore drilling and production platforms, wellheads, and pipelines.
The modern bird-foot (Balize) delta of the Mississippi River displays three major distributaries (Fig. I) and has formed within the past 600-800 years.1 Seaward progradation rates of the distributaries vary from in excess of 100 m/yr to less than 50 m/yr, depending upon the specific distributary monitored. Sedimentation rates seaward of the delta shoreline vary spatially as well as temporally. Near the mouths of the distributaries, accumulation rates in excess of 1 m/yr have been documented, whereas in adjacent interdistributary bays accumulation rates rarely exceed a few centimeters per year. In offshore waters, in front of the delta, accumulation rates vary from a few tens of centimeters per year in 50-m-depth water to a few millimeters per year in water depths approaching 200 m.
Offshore slopes of the entire delta front are extremely low, rarely exceeding 1.5°. In the interdistributary bays, bottom slopes are generally less than 0.5° and are rarely greater than 0.2°. In water depths of approximately 5-80 m, bottom slopes range from 0.7° to 1.5°, and in depths of 80-150 m the slopes are less than 1°. In general, hydrographic maps indicate extremely irregular topography, the bottom displaying a large number of radial trending submarine gullies 2 in water 20-80 deep and broad, flat terraces seaward to water depths as great as 200 m (Fig. 1).