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GoSimple autonomous inspection vehicles are suitable for operations where the cost, danger to humans, or area of operation prohibits the use of conventional underwater technology. Autonomous vehicles are, however, in their infancy and few such vehicles are available. There are still some problems to be overcome before this technology becomes useful in commercial applications. We have built ROV90 to investigate these problems.It is a test bed for experimenting with the different parts of an autonomous underwater vehicle. ROV9D will be able to autonomously follow prominent features In the real world, man made or natural. Examples are pipelines or walls in tunnels. ROV90 is tethered, but we are planning to use experience and results from ROV9D to develop a "real" AUV called PISCIS.

Today''s tethered ROVs Can carry out many of the operations for which a diver used to be necessary. The ROV''s maneuverability and range are, however, limited by the tether. The necessary surface support for a UUV or RCV adds much to the cost of ROV operations and makes it dependent on good weather conditions. Thus, there is a large potential for reducing the cost of traditional ROV operation by removing the tether and if possible, the surface support. On the other hand, an untethered underwater vehicle (UUV) have to have a much more advanced control system than the ordinary ROV. The reason for this is that a hydro-acoustic link is the only practical channel for communication underwater. Operator interaction is made difficult because this type of link has low band-width, transmission delays In the order of seconds, and limited range. The UUV must have a control system that can cope with the limitations of the hydro-acoustic

ISOPE-I-91-070

The First International Offshore and Polar Engineering Conference

Artificial Intelligence, Association, automatic control project, autonomous inspection vehicle, autonomous underwater vehicle, communication, control, ground transportation, inspection, Institute, management and information, Midstream Oil & Gas, nerov, November, pipeline, Piscis, project, remotely operated vehicle, shipbuilding industry, structural improvement, subsea system, technology, tokyo japan, vehicle

Industry:

- Information Technology > Robotics & Automation (0.88)
- Transportation > Ground > Road (0.70)
- Energy > Oil & Gas > Midstream (0.47)

SPE Disciplines:

Current methods of determining conductor setting depths are described. These are based on the assumption that existing overburden pressures develop the capability of the foundation to resist hydraulic fracturing. This leads to conservative results and consequently higher installation costs. In an attempt to reduce this conservatism, packer tests have been performed offshore in the St. Joseph field off the coast of Sabah in heavily over-consolidated clays, in order to measure the hydraulic fracture characteristics directly. This paper describes these tests , the equipment used and discusses the results, both in terms of recommendations for a reduction in the site specific conductor setting depths and by comparing them to existing hydraulic fracture theories. Following these tests, conductors at a nearby platform in the St. Joseph field, founded on an essentially similar clay, were installed at reduced depths in line with the recommendations from the packer test results. Conductor installation time was reduced by approximately seven days of jack-up rig time. Proposals for further work are given.

Conductors are required in the drilling of oil and gas wells to prevent the upper portion of the hole from caving in and water from entering and mud from leaving the hole. Offshore, they also protect the well casings from environmental loads. Typically they are 660mm to 762mm in diameter and, from a geotechnical point of view, the minimum setting depth below mudline should satisfy the following requirements: a) The conductor should have sufficient axial bearing capacity, derived from external frictional resistance alone, to transfer self weight and all external vertical loads on the conductor (e. g. blow-out preventors, initial casing hung off) to the soil.

ISOPE-I-91-025

The First International Offshore and Polar Engineering Conference

annular pressure drilling, clay, Conductor, contingency planning, Emergency Response, field, health safety security environment and social responsibility, hydraulic fracture, hydraulic fracture test, hydraulic fracturing, metre, metre penetration, mud, operational safety, packer, penetration, platform, SOIL, St Joseph, strength, test, testing, theory, Upstream Oil & Gas, well completion, well control, well integrity, zonal isolation

SPE Disciplines:

- Well Completion > Hydraulic Fracturing (1.00)
- Well Completion > Well Integrity > Zonal isolation (0.56)
- Well Drilling > Pressure Management > Well control (0.48)
- (2 more...)

van Wingerde, A.M. (Delft University of Technology) | Wardenier, J. (Delft University of Technology) | Puthli, R.S. (TNO Building & Construction Research) | Dutta, D. (Mannesmannrohren-Werke A.G.)

This paper provides fatigue design guidelines for T and X- joints of square hollow sections, based upon recent research results. Parametric formulae are established, which describe the relationship between the non-dimensional parameters (β, 2γ and τ) and the stress concentration factors, so that the hot spot stress range Sr can be determined. Design Sr-Nf lines have been determined on the basis of experimental work and parametric formulae. These lines have been compared with existing guidelines. The experimental work also serves to verify the validity of the numerical model.

This paper evaluates recent numerical and experimental work on T- and X-joints made with square hollow sections. This evaluation is part of the CIDECT research programme 7K "Fatigue Behaviour of Uniplanar Joints" (Wingerde, 1991b). The participating partners are: MannesmannrÃ¶hren-Yerke A.G., DÃ¼sseldorf, Verenigde Buizenfabrieken, Oosterhout, TNO Building and Construction Research, Rijswijk and the Delft University of Technology. The aim of this programme is to provide fatigue design guidelines for square hollow section joints. The nominal stress range

ISOPE-I-91-284

The First International Offshore and Polar Engineering Conference

It is shown using the slender ship theory that an ideal ocean wave focusing lens can be composed by an array of submerged circular cylinders. We performed experiments of wave focusing using Fresnel lenses of 20m long in a wave tank of 30mx 50mx 204m. The results show that a circular cylinder type produces higher wave height magnification than a flat plate type in both regular and irregular waves. Furthermore, effects of the lens'' slenderness, wave breaking on the lens, and nonlinear modulation of waves around a focal point are discussed both numerically and experimentally.

A wave focusing lens has been attracting ocean engineers as one of most promising wave control techniques. It helps effective utilization of wave energy and creates calm sea areas. In some previous works(Mehlum and Stamnes(1979), Stamnes et a1.(1983), Elldo et al.(1986)), a wave focusing lens was composed by a horizontally submerged flat plate and its performances were investigated. However, the reflected waves by a flat plate reduce the wave height magnification and increase the drift force on it. Then Einoshita and Murashige(l990a,b) first tried to examine performances of an ideal lens using the slender ship theory and next to determine the shape. As a result, Murashige and Kinoshita(1990) found that an array of submerged circular cylinders satisfy necessary conditions for its sectional shape. The present paper summarizes how we determine the shape and shows experimental results of wave focusing of two kinds of lenses of 20m long in a wave tank of 30mx 50mx 204m.

Let us consider perfect wave focusing of incident plane waves progressing in the positive x-direction on a focal point on the x-axis by an ideal lens placed along the y-axis within the linearized water wave theory.

ISOPE-I-91-147

The First International Offshore and Polar Engineering Conference

Gato, L.M.C. (Mechanical Engrg. Dept., Instituto Superior Tecnico) | de O. Falcao, A.F. (Mechanical Engrg. Dept., Instituto Superior Tecnico) | Pereira, N.H.C. (Mechanical Engrg. Dept., Instituto Superior Tecnico) | Pereira, R.M.R.J. (Mechanical Engrg. Dept., Instituto Superior Tecnico)

The paper deals with the preliminary design of the air turbine of Wells type for the prototype OWC wave power plant planned to be installed in the island of Pico, in the Azores. Several different configurations are considered, namely the monoplane and, the biplane turbines, including a modified version of the biplane rotor with staggered blades. Design methods based on two-dimensional and quasi-three-dimensional flow models are used to compare the geometry and performance of the turbines.

The paper deals with the preliminary design of the air turbine for the prototype OWC wave power plant planned to be installed in the island of Pico (population about 15 thousand), in the Azores. The power plant will stand on the sea bottom, adjacent to the rocky coastline. The horizontal axis air turbine, driving an asynchronous generator, will be installed onshore and connected to the OWC pneumatic chamber by a duct. The input data for the turbine design was provided by testing a 1/35-scale model of the power plant in an irregular wave tank, as well as by wave measurements on site. The air turbine to be designed is of Wells type. This is a self-rectifying axial-flow turbine which was invented in the mid-seventies by Dr A.A. Wells for wave power utilization. The original version of the Wells turbine has a rotor with a set of symmetrical airfoil blades, fixed to a hub, with their plane of symmetry normal to the axis of rotation. Versions of the Wells turbine have been studied with and without stationary guide vanes.

ISOPE-I-91-051

The First International Offshore and Polar Engineering Conference

Industry:

- Energy > Renewable > Ocean Energy (1.00)
- Energy > Power Industry (1.00)

Inoue, Yoshiyuki (Yokohama National University) | Miyabe, Hiroaki (Yokohama National University) | Weiyi, Xue (Yokohama National University) | Nakamura, Mauricio (Yokohama National University)

The quasi-static analysis is an easy and convenient tool to determine the maximum tensions of mooring lines of floating structure in wind and waves. Hence, it is frequently used in the initial stage of design of mooring system and dynamic analysis is used only for limited and special cases. Therefore, by dynamic analysis methods, getting stable and same results is difficult as in quasi-static analysis. By quasi-static analysis, however, it is difficult to estimate the dynamic effects of mooring lines and low frequency motions due to wind and waves. Accordingly, dynamic simulations of moored floating vessels in wind, wave and current are conducted in various conditions of sea states, mooring coefficients and vessels. The numerical results are shown in figures for the sake of explaining the effects of various kinds of external forces on the maximum and mean displacements of vessels which correspond to the tensions of mooring lines. Secondly, the authors investigate the dynamic analysis of tension of an assumed mooring line of these vessels in various conditions of motions of the mooring point by using the

In waves, floating vessels are subjected to frequency motions. In the case of moored floating vessels, in the horizontal plane, surge, sway, and yaw encounter additional low frequency motions caused by small restoring forces of moorings. The authors analyze the amount of the low frequency motion and its relationship with not only 2nd order wave drift forces but also with 2nd order non-linear forces, such as wind and current as a function of the sea state, denoted by the Beaufort scale.

ISOPE-I-91-097

The First International Offshore and Polar Engineering Conference

SPE Disciplines: Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems > Mooring systems (1.00)

Current design practice is to use Morison''s equation for the prediction of forces on nominally rigid tubular members of offshore structures and to assume that vortex shedding induced transverse forces are not sufficiently coherent over the whole span of a tubular to warrant separate attention. Recent experiments on marine and artifically roughened cylinders show large vortex shedding induced lift forces which have a hight degree of spanwise coherence. The paper shows, through a case study, that in some circumstances the combination of the inline force and the lift force produces a resultant much larger than the Morison force above and an even greater increase in cumulative fatigue damage

vortex shedding forces are normally considered in the design of flexible tubular members because of the problem of the tubular vibrating at the same frequency as the vortex shedding; the so-called “locking-on” phenomenon. However in the case of rigid tubulars it is generally considered that the vortex shedding is unlikely to be coherent over the whole span and the net transverse force will be negligble when compared with the in-line force. This is a plausible assumption when the global loading of a jacket is considered as the flow at any instant in time varies considerably over the space of the jacket. Indeed the flow may vary considerably over the span of an individual member particular for those inclined at an arbitrary angle to the flow direction. However for vertical members close to the seabed in relatively shallow water the fluid flow may have a high degree of coherence in relative severe weather conditions when the directional spread of the waves is small. In these circumstances the flow closely approximates the planar oscillatory flow found in U-tubes and oscillating cylinder experiment tanks.

ISOPE-I-91-195

The First International Offshore and Polar Engineering Conference

SPE Disciplines:

The present paper reports on some preliminary developments towards a simplified procedure to identify tubular joint damages which occur very often in fixed offshore framed structures. To this aim two small scale models were designed and constructed according results from the Similitude Theory. An experimental modal analysis technique was applied to obtain their dynamic characteristics. It is shown that certain common types of joint damages in these structures can be identified by looking at changes of some modal parameters.

Ever deeper waters in offshore oil exploitation has brought increasing difficulties for visual inspection of structural damages. These difficulties have enhanced the necessity for the development of monitoring techniques for damages identification by looking at changes in the offshore structure''s dynamic characteristics. The present paper reports on some preliminary developments towards a simplified technique to identify tubular joint damages which occur very often in offshore framed structures. Changes in dynamic modal parameters and responses can be determined best through careful laboratory experiments. To this aim two small scale models were designed and constructed according to the principles of hidro-elastic structural similitude. The modal characteristics of the initially perfect model are taken as references for comparing further results obtained from the same model in which some chosen joint damages were imposed. In both cases the modal characteristics were obtained through white noise type random vibration. The results were analyzed by the circle fitting method and the main dynamic parameters related to the first three flexural vibration modes and to the first torsional vibration mode were determined. Conversely to common sense expectations a preliminary analysis of the obtained results leads to the conclusion that the natural frequencies are almost insensitive to these damages. Nevertheless the response amplitudes, on certain conditions, present substantial variations.

ISOPE-I-91-228

The First International Offshore and Polar Engineering Conference

Country:

- Europe (0.68)
- South America > Brazil (0.47)

SPE Disciplines:

The intent of this paper is to exploit an alternative approach to the determination of intersections in mechanical parts by means of a routine based upon G1. Formula - an extension of the Netwon-Leibniz Formula.

Most solid mechanical parts are objects bounded by finite quadric surfaces. In practice, when numerically controlled machine tool is used in mechanical part processing, it is essential to know the precise coordinates of points in the intersections formed out of two or more interlaced bodies. For this purpose, there have existed some effective approaches which typically are based upon algebraic geometry.. The most influential one is the method devised by J. Z. Levin as outlined in Ref. 1 (Joshua Zev Levin,1978). In essence, Levin''s way to computing intersections is by using matrix algebra and parametric equations. Of high accuracy and. remarkable generality, such method has been in extensive applications. This paper, by introducing a set of sections, is intended to illustrate an alternative access to this problem, via which the ''determination of intersections can be transformed to a procedure of just specifying the crosspoints of the curves on that set of sections introduced. The main instrument utilized in this proposal is the ct Formula, a unified solution to intersection points. The underlying ideas of CL Formula is in agreement with the Newton-Leibniz Formula. For details, see Ref.9. Featuring uniform computational procedure for most cases and easy calculation, such method would see applications in many fields, e.g., serve as a additional mathematical model for auto-programming

ISOPE-I-91-065

The First International Offshore and Polar Engineering Conference

The paper develops design response spectra for fixed offshore platforms subjected to random wave loadings, in which the random wave is characterized by either a Pierson-Moskowitz or a JONSWAP spectrum. Each design response spectrum is obtained by taking the average of 100 response spectra from repeated simulations. The design response spectrum developed can be used directly for various sea states. This flexibility is attributed to the use of a standardized equation of motion. An example is given to demonstrate the efficiency and simplicity of using the design response spectrum. Due to its efficiency and simplicity, as well as its flexibility (applicable to various sea states) and reliability (developed based on sufficient number of simulations), the design response spectrum developed is recommended to be used during the preliminary design stages in order to estimate the maximum dynamic response of a fixed offshore platform.

The concept of a response spectrum has gained wide acceptance in structural dynamic practice, particularly in earthquake engineering design. Stated briefly, the response spectrum is a plot of the maximum response to a specific load function for all possible single-degree-of-freedom(SDOF) systems. Veletsos et al. (1983) first introduced the response spectrum concept into offshore engineering. Their study employed a SDOF system based on the assumption that the offshore structure vibrates only in its fundamental mode An important conclusion of this work was that the concept of a response spectrum is applicable to offshore structural design, at least at the preliminary design stage. Unfortunately, the response spectrum developed by Veletsos et al. is only appropriate for a particular sea state, with a significant wave height equal to 40 feet. If the response spectrum under a different sea state (different significant wave height) is needed, one would have to repeat the entire task of generating another response spectrum.

ISOPE-I-91-182

The First International Offshore and Polar Engineering Conference

Artificial Intelligence, design, design response, design response spectra, design response spectrum, displacement, Jonswap, JONSWAP spectrum, loading, normalized structural frequency, Offshore Structure, reservoir description and dynamics, Response, response spectrum, Simulation, spectra, spectrum, Upstream Oil & Gas, Wave

SPE Disciplines:

Thank you!