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ABSTRACT In this paper a combination of a shielding technique for underwater welding and a technique for shielding gas recycling is presented. Both of the techniques are based on centrifugal forces imposed to a two-phase fluid by a rotating impeller and are combined in one tool. Special emphasis is laid on the separation of the gas-water that is removed from the welding area. Experimental and theoretical investigations on the ~on quality and out he dynamic behaviour of the separator are presented. The shielding technique and the separation technique have been combined and the technical opinion of the combined tool was proved. INTRODUCTION Underwater welding is encountered mainly in the maintenance of underwater structures such as pipelines and platform legs in the offshore industry. Starting out from manual metal me welding processes in direct contact to the water or inside hyperbaric diving chambers (Ibara, et al. 1990, Sanchez. Osio, et al. 1993, Szelagowski et al. 1993), recent investigation focus on automated welding techniques with shielding techniques that remove water from the welding zone. These shielding techniques allow for low cooling rates and thus improve the weld quality. Also the hydrogen formation and the resulting hydrogen cracks are minimised by avoiding a direct contact of water and the plasma arc. Recent investigations on different kinds of shielding techniques have been carried out by Arata et al. 0987), Hoffmeister et al ((1991), Küster et al. 098"0, Hamasaki and Sakakibara (1984, 1978), Shinda et al. (1980, 1982), Coriatt and Roggen (1979), Draugelates et al. (1993, 1994), and Dos Santos et al. (1990, 1992). Most shielding techniques are based on water or/and gas impulse used for the removal of the water.
- North America > United States (0.28)
- Europe (0.28)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Gas cycling (0.61)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.53)
ABSTRACT In this paper, the flow around v-shaped plates placed in a uniform horizontal current is simulated by using a finite volume method and compared with the flow field visualized by a dye injection method. The flow properties are investigated particularly in viewpoints of the rising height of vortex head and the strength of the vertical convection, which varies with the configuration of the plate. The flow patterns are examined by varying the dihedral angle(Θ) and the inclination angle(Ø) and the optimum configuration which induces the strongest vertical convection flow is determined. 1. INTRODUCTION Recently, various structures such as floating plant and artificial harbour have been constructed in coastal region with a wide range of purposes. Such a facility disturbs the flow patterns around and may cause stagnant flow locally, which results in eutrophication and stratification of sea. It is therefore necessary to utilize an appropriate device to control the flow in favorable manner and to make the quality of seawater better. Sea flow control device usually needs successive energy supply, which makes it necessary to design the system to use natural energy such as current and wave. Some kinds of a simple structure, installed in sea may play an affirmative role by recirculating polluted seawater and refreshing it. In this paper, a v-shaped plate is focused as a seawater recirculating system. Hunt et. a1.(1980) revealed some flow phenomena of stratified fluid over three dimensional hill by a visualization technique. Takashi et. a1.(1990) experimentally investigated the upwelling flow artificially induced by v-shaped plate, which mixes the stratified stagnant flow. And it can be applied to mitigate eutrophication and stratification of sea in the vicinity of the offshore structure.
- Data Science & Engineering Analytics > Information Management and Systems (0.50)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.48)
- Reservoir Description and Dynamics > Reservoir Simulation (0.41)
Sea Engineering, Inc., and Precision Signal, Inc., have developed a new frequency modulated (FM) subbottom profiler capable of shaped pulses in a broad band of frequencies from 300 to 10,000 Ha. This project was funded by the Center of Excellence for Research in Ocean Sciences (CEROS) because off-the-shelf commercial systems were not able to generate images of Hawaiian shelf sediments with sufficient penetration or resolution for identifying sand resources. A new tow vehicle design contains four parallel 1.5 meter line arrays providing about 12 dB greater directivity than a streamer hydrophone array of the same length. The 12 dB reduction in scattering provides a large improvement in image quality. A range of pulses can be designed and individually selected to target specified survey requirements. During sea trials of the sonar, tests showed that the best images of the top 40 meters of sediments were collected using an FM pulse with a center frequency of 1.4 to 2.0 kHz and a bandwidth of 2 to 3 kHz Pulses with higher frequencies produced degraded images because attenuation and rough subsurface boundaries caused weak reflections from the subsurface structure. Preliminary surveys on O'ahu have produced the first clear images of sand and other calcareous sedimentary features, and have also delineated the underlying reef structure. The system is calibrated, and allows real-time quantitative analysis of the sonar data. Robust sediment classification software has been developed that uses the reflection data to provide surficial and subsurface measurements of compressional wave attenuation, acoustic impedance, and volume scattering. These three acoustic parameters are used to predict physical properties of the sediment such as grain size, bulk density, and porosity. Predictions are based upon empirical relationships derived from correlation studies of the acoustic parameters and sediment properties. Extensive ground-truth probing, and sediment sampling and analysis have established the accuracy of the system.
- Geophysics > Seismic Surveying (0.88)
- Geophysics > Borehole Geophysics (0.88)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.67)
- Data Science & Engineering Analytics > Information Management and Systems > Artificial intelligence (0.67)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (0.56)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.54)
ABSTRACT At Statoil's Research Center in Norway, experiments with underwater gas releases have been performed, with both an instantaneously started source and a continuous source. The objectives were to investigate the surface currents near the bubble plume, and the gas dispersion above the surface. The currents can cause stability problems for vessels or offshore platforms, high concentrations of natural gas can result in fires or explosions for releases occurring below or near offshore installations. The experiments were performed in a basin of 7 m depth with volumetric flow rates ranging from 0.083 Nm/s to 0.75 Nm/s, corresponding in scale to that expected from a full pipeline rupture or blowouts from shallow pockets. Measurements of water velocities and void fractions were performed in the vertical bubble plume and in the horizontal surface flow. The gas concentration above the water surface was monitored by means of a novel measuring technique: for these experiments, a mixture of helium and air was used to obtain the same density as natural gas. The velocity profile in the surface flow was found to be different from that observed by others: the profile depth was found to be decreasing with increasing distance from the center of the bubble plume, whereas previous work indicate an increase of profile depth due to entrainment. The horizontal transport of gas (bubbles) was found to be greater than expected: the gas was dispersed into the atmosphere from an area corresponding to about six times the area of the central boil region, in the present experiments the release rates were significantly higher than in previous investigations, and we observed a fountain of significant height above the reference surface. The return flow from this fountain penetrated deep into the water.
- Europe > Norway (0.66)
- North America > United States (0.46)
- Reservoir Description and Dynamics (1.00)
- Facilities Design, Construction and Operation (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.66)
- (4 more...)
ABSTRACT The 12,880 m long Confederation Bridge will be the world longest "spanned box girder bridge over salt water. Several design criteria for this bridge, with 250 m span length, 100 year design life and 4.00 to 4.25 safety index, are not covered ~ any code or standard. A comprehensive monitoring and research program is being carried out to monitor and study the bridge behavior under ice forces, short and long-term deformations, thermal stresses, traffic load and load combinations, dynamics, wind and earthquake, and corrosion. The measured data and research results will be valuable for design, analysis and construction of similar bridges and structures, also useful for management and maintenance of this unique structure. INTRODUCTION The Confederation Bridge will provide a surface link between Borden on the Prince Edward Island and Cape Tormentine in the: Province of New Brunswick across the Northumberland Strait. The crossing consists of forty-three main spans with span length of 250 m at the height of 40 to 60 m above mean sea level, and eleven approach spans. The cross-section for the bridge structure consists of a single prestressed concrete box with varying depths within each span. Post-tensioned prestressing, using both internally bonded tendons and external tendons, and segmental construction are employed for the superstructure. The piers are of the form of octagonal hollow shaft in the upper portion ending with a conical shell and a ring-shaped footing on the sea bed. This 12,880 m long, 11 m wide two lane bridge is the world longest spanned, box girder bridge over salt water. The design life of the bridge is 100 years, and its design procedure is not covered by any code or standard worldwide. This bridge is constructed and prestressed in segments in numerous stages, and will be operated under severe environment conditions.
- North America > Canada > Ontario (0.28)
- North America > Canada > Prince Edward Island (0.24)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.46)
The paper presents a kind of multi-function removable concrete platform suitable for marginal oil fields in the Bo Hai of China. Type selection and structure optimum of the platform are finished. The temperature distribution of the oil tank is calculated. The study provides the theory basis of platform structure design. The application of the new type of concrete platform should reduce the cost of opening up offshore oil fields, and promote the development of China offshore oil fields. INTRODUCTION With the development of offshore oil fields, it is not easy to find the large high-yield oil field. Some medium and small sized oil fields can't be opened up for the high cost of development. The offshore oil fields being developed in China are mainly medium and small sized oil fields with yearly production less than 1000,000 tons. Therefore, to reduce the cost of engineering facilities in the development offshore oil fields is an important problem of China. It is an effective way in the development of marginal fields to use the concrete platform. Some studies (Yupu Song, 1991) about the fixed concrete platform lying on hard soil layer have been finished. But the study about the removable concrete platform to be used on soft soil layer is seldom found. Presently, a kind of multi-function removable concrete platform suitable for offshore oil fields in the 13o Hai is developed by Dalian University of Technology and China Bo Hai Offshore Oil Corporation. In this paper, analysis and calculations about platform optimum and temperature distribution are given. The study prorides the theory basis of platform structure design. STYLE SELECTION The concrete platforms generally have three functions such as drilling, production and storage, but several self-elevating drill ships owned by 13o Hai Offshore Oil Corporation are enough to develop Bo Hai fields, and most marginal fields had pre-drilled weft.
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Yian Formation (0.99)
- Asia > China > Heilongjiang > Songliao Basin > Daqing Field > Mingshui Formation (0.99)
- Well Drilling > Drilling Equipment > Offshore drilling units (0.88)
- Reservoir Description and Dynamics (0.71)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.71)
ABSTRACT Norwegian oil companies, cable manufacturers and pipeline installation companies are presently conducting studies on electrical heating of multiphase subsea pipelines to prevent hydrate formation (plugs). The evaluation of technical feasibility and cost estimates have been completed both for a 50 Hz direct resistive heating system and for a system based on electromagnetic induction. The electrical rating of the systems depends on the heat requirement, pipe material and the pipe length. The feasibility of the concepts has been verified through full scale subsea tests. Results from the measurements are used to determine the characteristic parameters of the two systems on fields in the North Sea. The study includes both carbon steel, duplex steel and martensitic steel (steel of 13% Cr content) pipes, with diameters from 8" to 20". The heat requirement mainly depends on the thermal conductivity of the pipe insulation and seabed (gravel), and in the case of melting plugs, the heat capacity of the pipe, thermal insulation and the hydrate must also be taken into consideration. A temperature rise of approx. 20 deg. C above sea temperature is necessary to prevent plugs in pipelines during planned shut-downs or reduced flow rate. Calculations show that acceptable temperature requirements are achieved for thermally insulated pipes, both on the seabed and for buried pipes. With buried pipes, acceptable temperature conditions may be obtained without thermal insulation. A typical value of the corresponding heat requirement in the pipe is approximately 100 W/m related to a heat transmission coefficient of 5W/m °C for a 10" pipe. Due to the electrical heating, possible corrosion problems caused by alternating currents (AC) are investigated. The coherence between corrosion and current level has been evaluated. The tests indicate that the induction heating system implies no modifications of the conventional anode system.
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Metals & Mining > Steel (0.96)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (1.00)
- Facilities Design, Construction and Operation > Flow Assurance > Hydrates (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (0.70)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.68)
ABSTRACT We investigated the effect of flow state on the amplitude of vibration in three-dimensional flow-structure interactions at low Reynolds number. In particular, we used a parallel spectral element code to study transition in the wake of flexible cables and beams. We found that cables tend to enhance transition whereas beams tend to delay it. Consequently, at Reynolds number around 200 the amplitude of crossflow vibration of beams is approximately half diameter, which is about half of the amplitude of vibration of cables in similar conditions. 1 Introduction Fluid flows over flexible cylinders arise in many engineering situations, such as marine cables towing instruments, flexible risers used in petroleum production and mooring lines, and other marine applications (see [3], [12], [11], [5], [13]). It is therefore important to understand and be able to predict the hydrodynamic forces and motion of cables caused by flow-induced vibration. In previous work, we have used direct numerical simulation to investigate flow-structure interactions in two- and three-dimensions (see [2], [7], [8], [9]). We have used a simple string equation to model the motion of the structure thereby neglecting the effect of bending stiffness. In addition, due to great computational expense, previous simulations were limited to low Reynolds number. In the current work, we extend some of the preliminary findings of [9] for the effect of flow on the amplitude of vibration as the flow undergoes transition from laminar to early turbulent state. In particular, it was found in [9] that for cable-flow interactions, the amplitude of vibration increases from about half a diameter to one diameter, as the Reynolds number changes from Re = 100 to 200. As a reference point, we note that the wake of a stationary cylinder becomes three-dimensional and turbulent in the regime Re = 200 - 300 (see [6], [1] and references therein).
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (0.55)
- Data Science & Engineering Analytics > Information Management and Systems (0.35)
- Reservoir Description and Dynamics > Reservoir Simulation (0.34)
ABSTRACT A multiple CCD camera system for full field velocity and acceleration measurements using Digital Particle Image Velocimetry (DPIV) analysis methods is presented. A sequence of three or four single or multiple exposure frames can be acquired within sub-milliseconds of each other to enable velocity and both Eulerian and Lagrangian acceleration fields to be measured. This work will present some preliminary results for the velocity and acceleration fields measured beneath a plunging breaker impinging on a flat vertical wall. Introduction Particle Image Velocimetry (PIV) is a well established experimental technique which enables highly-detailed, instantaneous full-field velocity maps of fluid flows to be constructed. This is achieved by seeding the flow with small neutrally buoyant particles and illuminating the region of interest with a pulsed sheet of light. PIV has been used in a number of applications including studies of water waves and flows around marine structures with great success and is now widely accepted as a standard measurement technique (Adrian, RJ, 1991). The resulting image is then analysed by auto-correlation either part optically, part digitally in the case of photographic film, or entirely digitally. The limitations of this method are discussed in a previous paper by the authors (Dewhirst et. al., 1996), with a system constructed from multiple CCD arrays being found to be the best solution to the problems of low dynamic range and directional ambiguity in the velocity measurement, and the low frame rate of conventional CCD cameras. This approach has already been undertaken by numerous people using both two array systems and multiple array systems to produce high-resolution, high-frame rate cameras (Raffel, M, 1995, Willert, C, 1995, Racca, RG, 1992), and the result is a system which can capture a sequence of four images of the flow under investigation with any desired time separations.
ABSTRACT A wave propagation spectral model to second order of approximation is suggested, which provides the actual directional spectrum in decreasing depths, starting from the corresponding one in deep water. The model implements the procedure already proposed for shoaling, refraction and saturation processes by adding bottom friction; utilizes deep water directional spectra involving JONSWAP frequency spectra and frequency independent spreading functions; finally, it considers straight coastlines with slowly varying bathymetry, the extension to the usual three dimensional bottom not involving special difficulties. The bottom friction process is formalized through a scheme which gives the relevant directional spectrum for the effective flow regime (laminar, rough turbulent, smooth turbulent, transitional) in the bottom boundary layer, depending on the wave field and Nikuradse roughness parameter. The model was tested by comparing it with field data from Maa and the results are quite satisfactory. INTRODUCTION The mathematical models available to quantify the modifications of multidirectional random waves propagating in decreasing depths up to the breaker zone are generally based on directional spectra and they differ from one another in the processes considered and in the order of approximation. Recently, Rebaudengo Landó et al. (1996) introduced a second order spectral model [ADS]2 which takes into account the shoaling, refraction and saturation processes. The model needs the knowledge of the first order spectral model [ADS]1 deduced by Scarsi (1995) on the basis of both the [LW]1 model suggested by Le Méhauté & Wang (1982) for the shoaling and refraction processes and the [TMAR]I model proposed by Gentile et al. (1994) for the saturation process and it utilizes the procedure formulated by Laing (1986) for the specification of the second order spectra starting from the corresponding first order ones.
- Europe (0.47)
- North America > United States (0.46)