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ABSTRACT This paper describes a Bonjeans/Hydrostatics Program for Irregular Shaped Hulls such as catamarans, drill ships, and other exotic shapes. The user defines the hull at each station by a series of straight lines and circular arcs. From this hull definition the- B6njeansProgram computes area and area moments at zero and three degree heel. Tins allows the Hydrostatic Program to perform all calculations involving water plane area independent of half-breadth values. The flexibility of this program allows hydrostatic properties to be computed for a wide range of forms previously unworkable. To my knowledge, its capability is unique in the industry and can replace repetitive manual calculations with a quick and reliable computerized method. INTRODUCTION The incapability to perform Bonjean/Hydrostatics calculations on hull forms with a non-traditional shape such as catamarans, drill rigs, vessels with drill wells or tunnel sterns became apparently the Computer Branch, Maritime Administration, Office of Ship Construction, several years ago. At that time hydrostatic calculations for irregular hull. forms had to be carried out by hand. However, two programs in our Hull Scientific Program Package pointed to the capability of performing hydrostatic calculations on any hull form which could be defined as a series of straight lines and circular arcs. The Maraud Bo jeans! Hydrostatics Program provided the format for hull form definition and arrangement of Bo jeans data for mass storage. The MarAd Cross Curves of Stability Program provided the routines for computation of station areas and moments at any degree of heel. By relying on station areas and area moments to define water plane properties, the Hydrostatics Program described here can operate independent of half breadth values. This bypasses the difficulty of defining exotic water planes in a point by point manner prior to finding their areas and centers. Development of the program was contracted to CADCOM, Inc. of Annapolis, Maryland who, in addition, developed a subroutine to calculate area and moments for arbitrarily defined shapes. They also provided a method for the treatment of longitudinal discontinuities (breakpoints such as wells, platform supports etc.) to accommodate Simpson's Rule. Final debugging of the program and documentation for public distribution is now complete and can be obtained by writing: Maritime Administration, Computer Branch, ode 724, Washington, D. C. 20235. This paper treats the input and output of the Bo jeans! Hydrostatics Program with the Appendix devoted to definitions of the hydrostatic values. A semi-submersible drill rig has been used for illustrating the program, and the resultant hydrostatic values are compared with the independent naval architect's computations.
- North America > United States > Texas (0.28)
- North America > United States > Maryland > Anne Arundel County > Annapolis (0.24)
- North America > United States > District of Columbia > Washington (0.24)
Conventional shallow submersible vehicles depend on the pressure hull for buoyancy, but deep submersibles depend on some type of bulk material for buoyancy. As a consequence, the design of very deep submersibles requires new considerations on the vehicle weight. The purpose of this paper is to evaluate the many parameters which affect the boat weight to see which ones are most influential on total weight. To accomplish this objective, a simplified mathematical expression is derived which describes the total weight for a deep submergence vehicle. The expression contains both structural and nonstructural weight items. The structural items include the pressure capsule, outer hull, foundations, and hard tanks. The nonstructural items are the equipment, buoyancy material, and payload. Each weight item is then examined in detail to determine what parameters affect the boat weight. The results show that the greatest weight reduction is possible with the equipment. This is because the state-of-the-art equipment used for deep submersibles has a weight almost equal to three times its displacement, and to furnish sufficient buoyancy material in the boat to float such equipment results in a large weight penalty.
Results for these three hull forms have been presented in this paper. The re-righting performance of three yacht hulls· has been assessed experimentally. The three hulls are The fact that any sailing yacht can capsize is accepted considered to be representative of modern racing by many leading designers, sailors and researchers, yachts. It has been shown that two different (Dovell, 1999, Golding, 1999, Deakin, 1998 and de experimental techniques provide the same relative Kat, 1999). Once the initial capsize is survived (which results between the three hulls, leading to the same is more dependant on hull structure and onboard safety conclusions. Correlation of re-righting performance systems than hydrodynamics), the problem is then to reright with basic hydrostatic parameters has been shown for the yacht in an acceptable time. Experience has these three hulls, however a simple case when this shown that if the yacht takes too long to re-right, the correlation is non-existent is noted.
ABSTRACT Various offshore operations, typically the installation of jacket structures, require provision of temporary auxiliary buoyancy. The offshore industry has traditionally used buoyancy tubes and tanks fabricated in steel for these operations. This paper presents a feasibility appraisal carried out by the authors which addressed the feasibility of using air filled, reinforced rubber bags as temporary buoyancy aids. The results of the project show that the rubber buoyancy bag concept can substitute the conventiona1 steel tanks used for jacket installation. This paper suggests that significant direct cost savings can be achieved by substituting steel buoyancy tanks with reinforced rubber buoyancy bags without increasing the risk level for the installation operation of the jacket structure. Further app1ications of rubber buoyancy bags in offshore operations are al so proposed where temporary auxiliary buoyancy is required, for example, platform removal. INTRODUCTION The aim of this paper is to highlight in general terms, the potential offshore related applications for rubber buoyancy bags, and to show that their development for offshore related applications is both financially and technically feasible. The feasibility study carried out has specifically addressed the use of reinforced rubber buoyancy bags as substitutes for steel auxiliary buoyancy tanks for platform installation. FIXED STEEL PLATFORM INSTALLATION The typical installation procedure for large fixed steel jackets, is illustrated on Figure 1. After being transported to the offshore installation site on the deck of a barge, the jacket is launched and subsequently upended by controlled flooding of compartments. Once upright, it is maneuvered to the precise installation location before being finally ballasted down to the seabed. The jacket on its own is normally very close to being neutrally buoyant i.e. the weight of the jacket nearly equals its buoyancy. However, to perform the launch and upending with acceptable clearance of the seabed and sufficient stability, the jacket is required to have a reserve buoyancy (buoyancy in excess of jacket weight) of some 20-40% depending on water depth, jacket configuration etc. This reserve (additional) buoyancy has traditionally been provided by steel buoyancy tanks and tubes as indicated on Figure 1. The most commonly used steel tanks are of cylindrical shape. They are of a thin walled construction with internal ring stiffeners and typical sizes from 2m to 5m diameter. The design is predominantly governed by the hydrostatic pressure to be experienced during launch and upending. The weight to buoyancy ratios that can be achieved are in the region of 1:3 to 1:4, with the best ratio only obtainable for large diameter tanks designed for moderate hydrostatic pressure. Auxiliary buoyancy tanks are normally attached at the top end of the jacket to raise the centre of buoyancy and hence ease the upending operation. An alternative installation method for larger jackets has been introduced by the new generation of semi-submersible dual crane vessels. These have significantly increased the upper weight limit for lift installed jackets.
System Description The Foinaven riser and umbilical system comprises of 10 flexible pipes and 2 umbilical and provides production, test, gas injection, water injection and control for two drilling centre. The size and duty of the risers is as follows:- Drill Centre I 2 × 10" Production 2 × 8" Production/Test 1 × 10" Water Injection 1 × 8" Gas Injection I × Dynamic Umbilical Drill Centre 2 2 × 10" Production 2 × 8" Production/Test I × Dynamic Umbilical The design pressure for the system is 3689 psi (254 bar g). The configuration of the risers is a "pliant wave" (figure I) which is anchored to a gravity base structure by tethers and has buoyancy modules distributed along the lower end. The system is designed such that it can be released from the FPSO in extreme emergency conditions. Design Conditions The Foinaven field is the deepest ever application of a "pliant wave" riser configuration and has to withstand very high currents over the full water column of up to 2 m/s (3.9 knots), When combined with the 100 year design wave of 18 m (sign) this provided very harsh conditions for the design of the pipe (figure 2), the critical areas being the vessel interface, where a bend stiffener is required, and at the riser touchdown point where extreme near and far vessel positions resulted in the need for a hold back anchor to prevent pipe movement and subsequent over bending of the pipe. The large waves in the Atlantic also impose severe fatigue loading on the risers, the most critical risers being the gas and water injection risers, due to the high operating pressure within the system. Next to the environmental conditions the next major influence on the system design was the vessel offset. This is closely linked to the design of the mooring system for the vessel which was far more compliant than originally anticipated in the riser design. When procuring a floating production system the risers influence both the sub sea layout as well as the mooring system design. Care must therefore be taken in addressing this interface. If the interface is defined at the riser touchdown the cost benefit of manufacturing flexible flow line jumpers (especially the flow line to manifold jumpers) at the same time as the riser maybe lost. Also for the umbilical, vessel interface was one of the major challenges. The region that experiences the highest loads both with respect to tension and bending is found at the I-tube exist. Bend stiffener design as well as cross-section design is critical. At touch down two clump weights were needed, One main clump weight taking up virtually all the tension, leading to that the touch down area saw no tension at high bending. the resulting catenary below the tether clamp, however, induced such a high bottom tension in the extreme current and far vessel offset cases that the interface joint between dynamic and static umbilical was anchored to a second, smaller slump weight. Its role is to prevent axial movement of the interface joint thereby preventing potential unwanted configuration changes.
- North America > United States > Texas (0.29)
- Europe > United Kingdom > Atlantic Margin > West of Shetland (0.25)
- Europe > United Kingdom > Atlantic Margin > West of Shetland > Faroe-Shetland Basin > Judd Basin > Block 204/24a > Foinaven Field (0.99)
- Europe > United Kingdom > Atlantic Margin > West of Shetland > Faroe-Shetland Basin > Judd Basin > Block 204/19 > Foinaven Field (0.99)