bluuebunny/crossref_metadata_2025_split huggingface dataset:
Jackup Performance and Foundation Fixity Under Developing Storm Conditions
Authors: Hambly E.C. , Imm G.R. , Stahl B. 
Published: October 2008

ABSTRACT
The dynamics and foundation fixity of the Rowan Gorilla II jackup at Arbroath (308 ft water depth) in the North Sea have been investigated through a measurement program and an analytical study. The measurements, recorded during the winter of 1988/89, reveal the presence of a significant amount of foundation fixity during a storm which was almost an annual return period storm. A small reduction in foundation fixity does occur during this storm. The analytical study includes the effects of nonlinear hysteretic spudcan behavior, layered seabed conditions, and irregular wave loading, and has been calibrated using the results of the measurement program. The study compares static vs. dynamic analyses using different models of foundation fixity (none, linear and nonlinear). The study also gives a best estimate of the maximum jackup leg moment for an extreme event at Arbroath.

INTRODUCTION
Jackups have historically been analyzed using static analysis techniques assuming no foundation fixity. As jackups move into deeper waters and become more dynamically sensitive, the effects of dynamics and foundation fixity become more important and must be modelled if realistic results are to be achieved. Unfortunately, dynamic effects are difficult to model, and little full-scale foundation fixity data of jackups in storm conditions is available.
Amoco hired the Rowan Gorilla II jackup to drill at Arbroath in the Central North Sea during the winter of 1988/89. The water depth at this site is approximately 308 ft (94 m). Amoco saw this as a unique opportunity to investigate the effects of dynamics and foundation fixity in deeper water, and initiated the data collection and analytical effort described in this paper.

MEASUREMENT PROGRAM
A measurement program was conducted aboard the Rowan Gorilla II jackup at Arbroath from December 21, 1988, to January 16, 1989. The independent leg jackup is depicted in Figure 1 and described in Table 1. The measurement program consisted primarily of an infrared wave probe and a triaxial accelerometer, with some wind and current data also recorded. Figure Ib shows the locations of the wave probe and accelerometer, and the definitions of surge and sway directions. Measurements were recorded for 50 minutes of each hour.
The largest recorded storm was a 26 ft (8 m) significant wave height storm which occurred on December 24. Based upon the significant wave height, the individual maximum wave height is estimated to range from 44 to 49 ft (13.4 to 14.9 m), depending upon the assumed individual wave height distribution. The storm was slightly smaller than the expected annual return period storm (29 ft significant) for this site.
Jackup natural periods for different seastates were obtained from spectral density analyses of the acceleration records.
The Dry Transport of the Green Canyon Tension Leg Wellhead Platform by a Semisubmersible Heavy-Lift Ship
Authors: van Hoorn F. , Devoy S.D. 
Published: October 2008

ABSTRACT
A Tension Leg Platform poses unique challenges with respect to its dry transportability. The engineering that is required before such a transport can be effected is given step by step. The development of a new type of cribbing block is described. The predicted extreme design environmental conditions and resulting extreme motions are compared with the actual monitored weather conditions and motions. From the correlation, conclusions are drawn.

INTRODUCTION
On May 26, 1989, the first TLWP (Tension Leg Wellhead Platform) was delivered in the U.S. Gulf by a self-propelled semisubmersible heavy-lift ship. This ship departed Singapore only 41 days earlier after loading the TLWP by means of the float-on method, see figure 1. The dry transport of this platform broke new ground in various areas. The unique nature of the TLWP required various unorthodox solutions. Conventional design methods were revised and new materials were developed.
The Green Canyon block 184 TLWP was built by a shipyard in Singapore, Republic of Singapore, which contracted with a HeavyLift Transporter for the dry transport of the TLWP to Pascagoula, Mississippi, where it was to be final outfitted before installation in the U.S. Gulf.
Dry transport by a self-propelled heavylift vessel offers the highest degree of safety in combination with a minimum of environmental loads on the cargo.
A wet tow was not a realistic option given the distance of over 12,000 miles and an anticipated tow speed of 2 - 3 knots. Transportation by tug/barge was considered, but the increased safety of the self-propelled option proved to be the most attractive.
The TLWP is constructed from stiffened cylindrical shells. The truss deck is carried by four columns of 12.2 meters in diameter, 46.2 meters in height, spaced 42.67 meters apart (center to center). Pontoons, 7 meters in diameter, connect the four columns near the base.
At the moment of load-out, the TLWP's displacement was 8,400 T with its center of gravity at 31.8 meters above its base. The draft measured 8.3 meters, leaving a freeboard on the pontoons of 1.2 meters. These pontoons were outfitted with bollards to facilitate the connection of tugboats and winch wires during on- and off-loading.
Given the relatively small footprints of the columns, in combination with the fact that these would mostly overhang the carrier's 40 meter wide deck, four sponsors were required to increase the support area. Much attention was paid to the footprint loads in order to obtain the optimum support configuration.
The Installation Design and Analysis of the Oseberg 'C' Jacket
Authors: Allen A.P. , Bjørke M. , Saetrevik T. , Auraaen E.G. 
Published: October 2008

ABSTRACT.
The Oseberg 'C' Jacket utilises for the first time a fully fixed mating system for jacket to template mating.
This paper presents a brief review of the available installation options for eight legged barge launched jackets and demonstrates the potential saving for each option. The design and analysis of the post launch installation phases of the Oseberg jacket is then described with particular emphasis on the development, design, analysis and model testing of the template mating system.

INTRODUCTION.
The installation in June 1988 of the Oseberg 'C' drilling template in the Norwegian Sector of the North Sea marked the beginning of the second phase of Norsk Hydro's Oseberg Project. The 14000 tonne Oseberg 'C' jacket, will be installed in the summer of 1990, by Heerema in 108 metres of water. Production start-up from the 35000 tonne topside scheduled for October 1991 will provide a further 100,000 bbl from the field bringing the total daily production up to 340,000 bbl.
Feasibility studies on a variety of alternative substructures led to the final selection of an eight legged barge launched jacket, together with a preinstalled subsea template as the most cost effective solution.
Provision of a drilling template to achieve early production has been a proven method of field development for some years, significantly reducing the lead time required and allowing increased oil production early in the field life.
The installation of a fixed jacket structure over a sub-sea template, having been first performed in the North Sea in 1979 (Fulmar wellhead jacket) has since been carried out on a number of occasions with a variety of jacket weights ranging from Fulmar at 2500 tonnes to the larger structures such as the Ekofisk 2/4 k water flood jacket, South East Forties and Oseberg 'B' at 18500 tonnes which was installed in 1987.
To date these structures have generally relied on the vertical docking technique in which the jacket is upended to a hover position 10 to 12 metres clear of the seabed and progressively lowered over the template engaging up to three previously installed docking piles of varying heights. Engagement is achieved, with either a passive or active tapered male/female docking sleeve system, which first engages with a large lateral gap between the sleeve and docking pile and reduces as the jacket or sleeve is lowered to provide accurate jacket/template location and thereby ensuring satisfactory conductor tieback.
The pile/sleeve gap is required for operational targeting reasons and to ensure against wave induced resonant jacket behaviour as the piles are engaged and the jacket stiffness properties change. In addition this gap must account for fabrication tolerances in the pile and sleeve, and installation tolerances in the pile.
The Oseberg 'C' jacket uses a new fixed mating system, patented by a Norwegian Company, which was developed with the following objectives;
A New Dimension in Offshore Emergency Evacuation
Authors: Withers M.H. 
Published: October 2008

INTRODUCTION
It is ironic, if not tragic, that after some ±25 years in the offshore oil and-gas sector, in a real emergency one of the valid, possibly in some cases only, means of escape from an offshore platform is to jump.
To address this problem, much thought was applied around 1982/3 with the result that, today, there exists a viable and we feel, more effective means of escape from a dangerous offshore incident. While the basic thought behind the system is to provide an integral part of an overall safety philosophy the system may, in some cases, be considered as a first, rather khan "last ditch", means of escape.
The basic requirement was therefore to provide a safe, rapid means of mass transfer away from the danger area. The system called for–Maximum capacity and availability–Minimum risk to system users
The key design criteria for the system are those of:–Simplicity–Functionability–Flexibility

THE PRODUCT OVERVIEW
In terms Of translating conceptual requirements into hardware, the first consideration had to be given to the means transfer to sea level responding to the criteria and demands noted above. Through long and painful development the chute design was evolved of which more later. A relatively simple matter was to add the necessary interface to the platform, deployment and means to transport away from the area. In block form the final solution appears as shown in Fig 1.
Fig. 1 (Available in full paper)
The four integral components of the system may likewise be depicted as shown in figure 2
Fig. 2 (Available in full paper)

THE CHUTE
The heart of the system and the real invention is the patented chute consisting of a series of modular cells running from the proposed evacuation deck level to sea level. Each cell, one meter long, contains a speed retarding slide mounted in the opposite angle to that in the cell above and below it. The outer tube and internal slides are all made of Aramid Fibre netting. It will be seen that this enables the evacuee to control, to a highly accurate degree, his rate of descent. Ref. Fig. 3
Fig. 3 (Available in full paper)
Each cell is separated from the next by are aluminium ring set, as mentioned, at one meter stages. The foot of each contra-angle slide, stops short of the outer diameter of the ring thus forming a "D"-section through which the evacuee enters into the next cell. The bar of the "D" is, in fact, a stainless-steel spring which adjusts to the shape "D" the body as the evacuee passes to the next cell.
Behavior of Pile Plug in Sandy Soils During and After Driving
Authors: Brucy F. , Meunier J. , Nauroy J-F. 
Published: October 2008

ABSTRACT
When open-ended piles are driven into the soil, a soil column is created inside. The advance of the soil column with respect to the pile penetration reflects the mode of pile penetration in the soil and influences the pile- soil interaction during and after installation. Formation of the soil co1umn inside open-ended model and large sca1e experimental piles was analysed at four sandy sites. The incremental filling ratio was found to be linked to the impact characteristics. The influence of the soil column on driving results as on static results was evaluated and discussed. In contrast to the driving results, the static loading result were not changed by the removal of the soil column. The plugging effect was explained by an exponential cumulation of stresses inside the piles.

INTRODUCTION
The majority of offshore platforms are founded on open ended tubular piles. When the piles are driven into the soi1, a soi1 column is created inside the pile. At the start of penetration, the pile cores a soi1 column the height of which is equal to the pile penetration. Then as penetration continues, the filling ratio may vary. At a certain stage, the soil column may act as a perfect plug, preventing any new soil intrusion. If that occurs, the pile penetrates the soil as a closed-ended pile. The advance of the soil column with respect to the pile penetration reflects the mode of pile penetration in the soil which influences the pile-soil interaction during and after installation. In practice the advance of the soil drivability methods use unit skin friction and unit toe resistance independent of the penetration mode of the pile. The contribution of the soil co1umn to the soil resistance to driving and to the static bearing capacity is taken as the lowest resistance of the two fo11owing mechanism. The plugged mechanism requires that the point resistance be calcu1ated over the full pile toe area, and the unplugged mechanism requires that an interna1 skin friction due to the soil co1umn be added to the point resistance of the pile annulus toe area. The same unit skin friction as the external on is used. This may be overly conservative for static design. In this paper, the advance of the soi1 co1umn inside experimental piles is reported -and analysed. The contributions of the soil column to the soil resistance to driving and to the static bearing capacity are evaluated and discussed. Open ended model piles 70 mm in diameter and 2,50m long and large scale piles 324 mm in diameter and 12 and 24 m long were tested at dense sandy sites. The experimental programme was carried out within CLAROM (a research association grouping French oil companies, contractors, one certification body and research institutes working on offshore operations).
A New, High-Frequency, Broadband Seismic Source
Authors: English J.M. , Inkpen S.T. , Guigne J.Y. 
Published: October 2008

ABSTRACT
A new seismic source has been developed which emits a reproducible, high frequency, broadband acoustic signal. This device, suitable for marine sub-bottom profiling is a unique variation of the multi-electrode sparker source. Calibration experiments performed in "free field" conditions have shown that the output is tunable by varying the power supplied to the source. Typical output has a 4.2 kHz bandwidth and a 3.0 kHz centre frequency, measured 3 dB down, at an operating power of 480 Joules.

INTRODUCTION
Resolution of two seismic reflectors depends on the length of the acoustic pulse. Simply put, the shorter the pulse, the finer the temporal resolution. Taken to the extreme, the ideal pulse would be a spike with all the energy concentrated at a single point in time. Since bandwidth increases with decreasing pulse length, the desired pulse is broad band, containing high frequencies to permit resolution of thinly spaced reflectors, as well as low frequencies which achieve greater sub-surface penetration. [1]
For a given pulse length, the desired shape is 'front end loaded'; having its energy maximally concentrated at the onset. [2] Such a pulse is known as minimum phase. Digital statistical deconvolution processes assume that the source wavelet is minimum phase. The quality of the output from these deconvolution processes degrades as the pulse departs from minimum phase.
An acoustic source which delivered the same acoustic signature for an indefinite period of time would reduce the possibility of interpreting a deviation in source signature as a lithologic change in the subsurface. Finally, an ability to control and alter the length and shape of the emitted pulse would permit a tuning of the source to a particular seabed.
In summary, good quality seismic data depend, among other things, on the length, shape and consistency of the downgoing acoustic pulse, as well as on an ability to alter the pulse in a controlled manner. We have developed an acoustic source based on the common sparker source routinely used in sub-bottom profiling. The conventional multi-electrode sparker has many advantages including its ease of operation, versatility and low cost; however, it does suffer from a degradation in pulse shape through the course of a survey due to the deterioration of electrodes. [3] Our efforts have concentrated on engineering a multi-electrode sparker that emits a minimum phase, reproducible signal with a higher frequency and a broader bandwidth than the conventional sparker. This device was developed specifically for the unique requirements of a stationary high resolution geophysical site surveying tool. [4][5] However, calibration of the source in a towed mode is planned for the next phase of our research. This paper describes the source and shows examples of field data.

SPARKER THEORY
The term sparker is misleading, it tends to imply that the mechanism is the same as that of a spark plug. However, a spark plug is a device which includes a pair of electrodes with an insulator in the inter-electrode space.
Simulated Turbulent Flow and Forces Around Groups of Cylinders
Authors: Hansen E. Asp , Yde L. , Jacobsen V. 
Published: October 2008

ABSTRACT
Results from numerical simulations of flow at high Reynolds numbers around cylinders and associated forces are presented. The numerical model is based on the discrete vortex model combined with an integrated boundary layer model. Hereby it has become possible to include the influence of the pipe roughness on the flow and the associated forces. The paper summarizes the theoretical basis for the model, including the boundary layer part and a simple approach for including the diffusion of rotation. Results obtained from the simulations with arrays of 2, 4 and 8 cylinders are presented. Steady flow and oscillatory flow cases are covered.

INTRODUCTION
An extensive amount of experiments to determine hydrodynamic loads on single cylinders has been carried out and reported in the literature. Within the last decade or so, increasing attention has been given to the determination of forces on more complex structures, such as riser bundles (Ottesen Hansen et al /1/, Overvik et al /2/), conductor arrays (Heideman and Sarpkaya /3/), and the complex joints of steel jackets (Velk and Sterndorff /4/).
When a cylinder is located in the downstream wake of another the force on the rear cylinder is typically smaller than on the one in front. This phenomenon is often referred to as 'shielding effect'. If, on the other hand, the same two cylinders are placed side by side in close proximity, the total force on the two becomes larger than the sum obtained from two isolated cylinders. This is referred to as 'blockage effect' or 'negative shielding effect'.
Model tests and full scale measurements on jacket type structures have clearly demonstrated the shielding effects in steady current flows, see e.g. Lambrakos et al /5/, and Cuffe et al /6/. Reductions in total loads of up to 40 - 60 percent were found for structures with large conductor arrays. In wave flows, the shielding effects may be less significant, Cuffe et al /6/, Sterndorff et al /7/.
The blockage effect was demonstrated for the simple 2 cylinder case by Jacobsen et al /8/. A system with a small and large pipe in close proximity resulted in load increases of up to 85 percent as compared to a 25 percent increase in exposed area for the side by side arrangement. For the tandem arrangement the total load was smaller than the load on the large pipe alone.
For groups of cylinders it is not trivial to evaluate whether the total force becomes smaller or larger compared with the situation where the cylinders are separated. Depending on the flow conditions and flow angle a group of cylinders may exhibit increase as well decrease in load compared to the separated cylinder case. Individual cylinders in a group will experience reduced load, others increased load. Detailed analyses and testing are required to assess the loads on cylinder groups.
In the present paper numerical results are presented for total and individual loads for systems containing 2, 4 and 8 cylinders.
Design of Gas and Oil Riser Installations for Offshore Platforms
Authors: Coker J.W.A. 
Published: October 2008

ABSTRACT
The Piper Alpha (ref. Ocean Industry Jan 1991) accident has focused attention on the design of riser installations offshore. As shown in this incident two major factors must be considered when designing riser installations. These are:to reduce the possibility of a dangerous event on a platform affecting the risersto reduce the consequences to an acceptable level if a riser failure occurs. There are many ways to design the installation so that the safety is at an acceptable level but this can be very dependant on the type of platform and function. The riser installation could, for example, be different if a concrete substructure is used instead of a jacket substructure.
This paper will indicate the various riser schemes used on installation today, outline the riser installation philosophy adapted for the latest Statoil designed platform and discuss how further installations can be designed to ensure acceptable safety at minimum investment cost.

INTRODUCTION
The risk associated with offshore installations for the production of oil and gas can, in principle be, divided into various risk areas. Different criteria can be used for the risk to personnel, the environment, or the risk to the capital investment. The risk can also be divided into the risk from design accidental events and residual events. The design accidental events are scenarios that the installation is designed to survive with acceptable damage to the personnel protection systems or/and the investment. The residual events are scenarios where it is likely the installation will suffer major damage or total loss.
The installation and equipment should therefore be designed such that the probability of the residual event is as remote as possible, within reasonable financial and practical considerations. The acceptance criteria must be decided on a company to company basis.
From the various studies carried out, which are backed up by the statistical data, the indication is that two types of platform (onboard) incidents can result in total loss of the installation. These are loss of control over the production wells and failure of the gas or oil risers. Both these type of events could lead to large releases of hydrocarbons over a long period of time.
The arrangement and design of the risers is therefore an very important parameter that must be considered during the design of offshore installations. With careful design it is possible to reduce the probability and consequence of a riser failure to a minimum, and to ensure the incident is contained into one area of the installation, at least for the time to allow safe evacuation of personnel.

RISER INSTALLATIONS ON EXISTING INSTALLATIONS IN THE NORTH SEA
Most of the early installations in the North Sea used a steel jacket design where the riser(s) was clamped to one of the main legs (ref. figure 1). The location of the riser was often decided by the arrangement of the process or metering systems.