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**Industry**

**Oilfield Places**

**Technology**

A nonlinear, 6 degree-of-freedom maneuvering dynamics and control simulator for the Theseus autonomous underwater vehicle (AUV) has been validated against several sets of full scale trials and independent predictive methods. The vehicle hydrodynamic coefficients are estimated with standard theoretical and empirical methods augmented with towing tank test results. The control algorithm implemented in the simulator is the same as the one used in the actual vehicle. A propulsion model makes it possible to optimize vehicle range and transit speeds as the battery capacity changes during the mission. The simulated vehicle response compares well against full scale sea trials data. The paper discusses the simulator validation and its use for vehicle design and mission applications.

In 1992, Defence Research Establishment Pacific (now amalgamated with Defence Research Establishment Atlantic (DREA)) contracted ISE Research Ltd. (ISER) to build an AUV capable of laying cable under Arctic ice. ISER designed and built the Theseus AUV shown in Figure 1 for a 450 km range, a cruising speed of 2 m/s, a working depth of 1000 m, and with variable ballast tanks fore and aft. With a 2.44 m long by 1.12 m diameter payload bay and additional ballast tanks to correct for deploying cable, Theseus can lay up to 220 km of fiber-optic cable in its current configuration. The vehicle has a modular design for ease of transport, fault-tolerant control software, navigational accuracy to better than 0.5% of distance traveled (cross track error is much better), acoustic and fiber-optic telemetry systems, and terminal acoustic homing (Ferguson et al, 1995). In April 1995, Theseus went on its first Arctic mission in the ice covered waters offEllesmere Island, Canada. The successful trial verified launch and recovery procedures, tested all vehicle systems in an under-ice environment (navigation, telemetry, cable deployment, etc.)

ISOPE-I-00-155

The Tenth International Offshore and Polar Engineering Conference

Industry:

- Information Technology (0.54)
- Energy > Oil & Gas > Upstream (0.48)

SPE Disciplines:

Friction welding of 5056 aluminum alloy similar material was carried out in order to examine the relationship between heat input and joint performance. The joint performance is evaluated by tensile test. The heat input is a heat source for welding solid materials and is classified into six categories, viz. friction heat input and deformation input during friction stage, upset stage and total stage. The most important heat input for evaluating the joint performance among these heat input was experimentally investigated through the tensile strength of welded joints because the friction mechanism is much complex. It was found that the deformation heat input during the upset stage was correlated well with the joint performance, and the sound joints were obtained with the deformation heat input over 100J/s. Moreover, it was recognized that the sound joints could be obtained with upset burn-off length over 2mm.

Friction welding is applied in many fields because of welding of round bars is easy, welding of the dissimilar materials is possible and so on. However, the friction welding process has complicated mechanisms, due to the heat source is the self-heating and the heated plane becomes directly the welding plane (Fukushima and Hasui, 1972). Therefore, the fundamental welding mechanism has not been clarified yet, then the setting of the appropriate welding condition is difficult for some materials and moreover the optimum welding condition also varies with friction welding machines. The aspect of the friction surface varies with the welding time during the friction welding, because the friction surface is constantly pulled out generating a burr (Hasui and Fukushima, 1975). Therefore, whether which time heat input during the welding process contributes to the welding is uncertain.

ISOPE-I-00-340

The Tenth International Offshore and Polar Engineering Conference

Soerensen, H.C. (EMU, Energy & Environment Consultancy) | Larsen, J.H. (Copenhagen Environment and Energy Office,KMEK) | Olsen, F.A. (SEAS) | Svenson, J. (SEAS) | Hansen, S.R. (EMU, Energy & Environment Consultancy)

The Middelgrunden project is an offshore wind farm with a rated power capacity of 40 MW. The contracts have been signed December 1999, and the park will be operational in the autumn 2000. The project consisting of 20 wind turbines at each 2 MW, will be situated just 2 km outside the Copenhagen harbor on shallow water (3-5 meter depth). The use of the area is restricted due to its former use as a dumpsite for harbor sludge. The wind farm is owned fifty/fifty by a wind energy cooperative and the Copenhagen Utility. This article summarizes the experiences from the planning of the project, and draws the perspectives for the future development of offshore wind power in Europe.

Today more than 100,000 Danish families are members of wind energy cooperatives and such owners have installed 80% of all Danish wind turbines. Until recently, the cooperatives were a very important and dominant factor in the development of the Danish wind energy sector (see figure 1). Since then, single person ownership has by far superseded the importance of the cooperatives. In the coming years the utilities are expected to play an increasing role in the establishment of large-scale offshore wind farms. The program of the Danish utilities alone has a total power of 750 MW within the next 8 years (The Offshore Wind-farm Working Group, 1997; Svenson et. al., 1999). The Middelgrunden project has obtained planning permissions in May 1999 and formal political approval from the Danish Energy Agency in December 1999. Contracts with the turbine manufacturer and the foundations and grid contractors have been signed in December 1999. A long-term contract governing the wholesale price of the energy production of the farm, as well as grid connection costs are currently being negotiated with the Danish Energy Agency.

ISOPE-I-00-070

The Tenth International Offshore and Polar Engineering Conference

SPE Disciplines:

Kamesaki, K. (NKK Corporation) | Shimazaki, K. (NKK Corporation) | Kasui, K. (NKK Corporation) | Matsumoto, H. (Japan National Oil Corporation) | Frederking, R. (National Research Council of Canada) | Timco, G.W. (National Research Council of Canada) | Sayed, M. (National Research Council of Canada) | Tseng, J. (Sandwell Engineering Inc.)

This paper examines a preliminary design aimed at evaluating the cost of a gravity based structure in the Sea of Okhotsk. Emphasis is placed on a simplified design for the ice belt zone of the structure in order to reduce the cost. The present work includes a method for estimating first-year ice loads on the structure. The method consists of analysis of actual ice data obtained for the Molikpaq structure in the Beaufort Sea, combined with numerical simulations. The results give global ice loads forl00-year return period and a new pressure-area relation.

The development of oil and gas in the Sea of Okhotsk faces several technical challenges, which reflect on the required capital expenditures. Reducing the cost of drilling structures is considered the key to success of that development. Such costs, however, remain uncertain. The uncertainty is mainly the result of the lack of well-defined functional requirements for the structures and corresponding designs. Ice loads on the structure are particularly considered to have a significant efl~ct on the design and cost of the structure. Therelbre, accurate ice load estimates and reasonable design methods are important Ibr developing cost effective structures. With this background, Japan National Oil Corporation, NK_K Corporation, the National Research Council of Canada (NRC), and Sandwell Engineering Inc. initiated a three-year research project in 1996, aimed at developing accurate estimates of ice loads and a reasonable structure design. In the first year, the influence of ice conditions on the design and ice load estimate methods were investigated. In the second and third years, field measurements were compiled and analyzed in order to obtain more accurate results, and preliminary numerical simulations were compared to other proposed load estimation methods (Frederking et al., 1999a and Timco et al., 1999b).

ISOPE-I-00-086

The Tenth International Offshore and Polar Engineering Conference

SPE Disciplines:

This paper presents an application of a patent technique (the patent number is ZL94 20404.2 in China) called Fan Weathervane Multi-point Counterweight Mooring (FWMCM). The feature of the technique is to apply the weathervane effect of the single point mooring system and additionally install the counterweight to conventional multi-point mooring system to reduce the mooring load and the occupied water-area. This new system may be utilized even in severely limited water-area for discharging of product oil and liquid goods economically. The FWMCM system technique had been utilized in a engineering project at Long Men Harbor in Qinzhou Bay, Guangxi province, China, which was an ideal selection for this project. There were two oil transfer terminals that adopted the type of FWMCM system in this project; one is for 50,000-ton terminal with 4 million-ton annual transfer capacity, and the other is 20,000-ton terminal with 3 million-ton annual transfer capacity. Computer simulation and tank model tests had been carried out, the results had shown that the FWMCM system was a novel and advanced mooring system.

The traditional fix jetty dock were mostly utilized to handling oil storage before the appearance of the single point mooring system in late 1950s in the field of large terminal of oil storage and handling in the sea. Nevertheless, the conventional multi-point mooring system technique is still an choice for mooring systems in the sea. The Traditional fix jetty scheme has the advantages of being direct connection between the jetty and the tanker, convenience in transportation and operation, but it suffers from the defects of being large investment, long construction period and poor stand capability to environment loads. The single point mooring system has the characteristic of weathervane, which always keeps the moored oil tanker at the least combined load position in wind, waves and current.

ISOPE-I-00-125

The Tenth International Offshore and Polar Engineering Conference

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

This paper presents a method of generating a strongly asymmetric wave in irregular wave train and a brief discussion of the effect of the waves on ringing response of a tension leg platform (TLP). Strongly asymmetric waves are usually generated in transient wave mode. Hence, the response data is too short for statistical analysis of the response to random seaways containing strongly asymmetric waves. To solve the above problem, we generate large numerical irregular wave elevation time series from a JONSWAP spectrum by varying the significant wave height, average wave period, vertical asymmetric factor and overshoot parameter. There, in the foregoing wave, we search for a zero down crossing period wave with the largest crest, and distort the wave to produce a strongly asymmetric wave in the physical wave train. The strongly asymmetric wave in the random wave train can produce a weak impact load on a TLP model fixed in the wave tank. The above wave loads can be used for the simulation of the ringing in TLPs.

To study the distribution of extreme ringing load of TLP tendons, we had generated a strongly asymmetric wave in an irregular wave train at the Texas A & M University (TAMU) wave tank (Zou et al, 1997, 1998). In the above works, however, details of the wave generation could not be addressed due to the tack of space. This paper is intended to detail the method of strongly asymmetric wave generation in the wave tank. In addition to the above, we will briefly discuss the wave effect on impact and the statistical criterion of ringing of a TLP. In nature, strongly asymmetric waves may be generated by the wind whose pressure is higher on the back than on the front of the crest.

ISOPE-I-00-229

The Tenth International Offshore and Polar Engineering Conference

Densely-sampled internal wave data obtained from an experiment in the Yellow Sea are presented. Large amplitude, low-frequency internal waves with asymmetric waveforms are clearly seen in the strong seasonal thermocline. Deterministic and in particular statistical properties of these nonlinear internal tides are analyzed. It is found that their probability distributions are positively skewed and have higher peaks than the corresponding normal ones. The deviations from the normal are measured by the skewness and kurtosis coefficients.

Internal waves occur within marine subsurface layers that are stratified due to temperature and salinity gradients. These waves, at scales from a few hundred meters to tens of kilometers, have a significant role in the energy and mass transport within the ocean. They can influence offshore engineering operation, undersea navigation, and even biological productivity (Wang, 1999; Wang and Gao, 1999). Internal waves on the continental shelf have been extensively studied, and an overview has recently been given on remote sensing and in situ observations of internal tides, solitary waves and bores in shallow water by Wang and Gao (2000a). Longwavelength solitary waves of height as large as 8m were observed during the 1984 SAR internal wave signature experiment conducted in the New York Bight (Gasparovic et al, 1988). The evolution of an internal tide was measured on the Australian North West Shelf in 1992. Solitons of approximately 40m height were observed between slope and shelf moorings. A numerical solution of the KdV equation, including horizontal variability and dissipation, was used to model the transformation of an initially sinusoidal long internal wave representing the internal tide (Holloway et al, 1997). A large-scale shallow-water internal wave acoustic scattering experiment was performed in the shelf region off the coast of New Jersey in 1995.

ISOPE-I-00-241

The Tenth International Offshore and Polar Engineering Conference

At 1:47 a.m. on September 21, 1999, Taiwan was slammed by its most powerful earthquake measuring 7.3 on the Richter scale in 100 years, struck central Taiwan near the small town of Chi-Chi, Pull Township just 6.9 km from the earth''s surface near the epicenter. The shock source time function has a total duration of about 40-sec, the quake had caused over 10,000 casualties, including more than 2,000 deaths. Over 10,000 homes had collapsed. Roads throughout much of Taiwan were rendered impassable and rail traffic was disrupted. Rescue teams spent most weeks searching for survivors in the rubble, and towns across the island struggled to hold last rites and bury the victims.

At 1.47 am on September 21, 1999, an earthquake measuring 7.3 on the Richter scale rolled outwards from its epicenter 12.5 km from Sun Moon Lake in mountainous central Taiwan, Nantou County. It was only 10.0 km below the Earth surface. The slip distribution thus obtained is quite consistent with the field as an average of about 2-3 m slip along the fault and a maximum slip of about 7-8 m at about 40 km to the north of the epicenter. There were extensive surface ruptures for about 85 km along the Chelungpu faultwith vertical and left lateral strike-slip olivet. The maximum displacement of about 9.8 meters is among some of the largest fault movement ever measured.

While three major quakes in just over a month since August 1999, the world is hit by 18 earthquakes measuring 7.0 or greater every year on average. The three recent large quakes were all probably difference in nature, Taiwan''s quake is classified as the "thrust-fault" type. Where one plate slides under another, while Turkey''s was a case of two plates grinding against each other.

ISOPE-I-00-158

The Tenth International Offshore and Polar Engineering Conference

Industry:

- Government > Regional Government > North America Government (0.46)
- Energy > Power Industry > Utilities (0.46)
- Energy > Oil & Gas > Upstream (0.34)

Oilfield Places:

- North America > United States > Montana > Lake Basin (0.98)
- North America > United States > Louisiana > Many Oil Field (0.98)
- Asia > Taiwan > Taichung Basin (0.98)
- (3 more...)

This study uses the boundary perturbation method to investigate the motion of a slightly distorted circular cylinder around another circular one. An approximate complex velocity potential is derived by means of successive images. The hydrodynamic interaction between these cylinders is computed based on the dynamical equations of motion. In a relative coordinate system moving with the uniform stream, the kinetic energy of the fluid is expressed as a function of fifteen added masses. Approximate analytical solutions of added masses in series form are obtained and applied to determine the trajectories of a slightly distorted circular cylinder around a fixed circular cylinder. Numerical results show that the initial configuration of the slightly distorted circular cylinder has a decisive influence on the development of its subsequent rotational motion.

Accurate prediction of the motion of a body moving around another in an unbounded fluid and determination of the hydrodynamic interaction between them have a variety of applications to the polar and offshore engineering. For example, when an ice floe moves near an offshore structure, the hydrodynamic interaction between these bodies becomes significant. Therefore, in the design of an offshore drilling platlbrm in the arctic region, engineers may have to consider the motion of drifting ice floes, conveyed by a stream, around the platform, and to predict whether the drifting body would collide with the platform. In practical cases, the Reynolds number based on the characteristic size of the offshore structure is usually large, the potential-flow theory would provide a good approximation of physical situations (Wu and Landweber, 1960) and the effect due to the fluid viscosity may be dealt with separately (Mofison et al., 1950; Sarpkaya and Isaacson, 1981). The problem of two parallel circular cylinders translating in an unbounded fluid was first considered by Hicks (1879).

ISOPE-I-00-270

The Tenth International Offshore and Polar Engineering Conference

This paper describes an investigation of the influence of hydrodynamic damping on the hydrodynamic loads and fluid surface elevations in a ship tank undergoing multiple component motions. A theoretical damping model for horizontal and vertical baffles in the tank has been developed. Experimental measurements of hydrodynamic damping have been carried out to validate the theoretical model, and to investigate the effectiveness of various baffle configurations. It is found that baffles can be used efficiently to damp liquid motions near resonant conditions.

The prediction of hydrodynamic loads on fluid-filled tanks in ships subjected to multiple motions in waves, particularly roll motions, is often an important requirement in design. Significant energy dissipation within the fluid may modify the extent of the sloshing and thus the magnitude of these loads. In particular, energy dissipation may occur on account of flow separation effects as the fluid oscillates past baffles or other obstacles in the tank. Faltinsen (1978) presented a numerical method for studying nonlinear sloshing in rectangular tanks, and modelled the hydrodynamic damping by assuming this to occur at the free surface through a modification to the free surface boundary conditions. Using Faltinsen''s approach, Isaacson and Subbiah (1991) obtained a closedform solution for a rigid circular tank with some level of energy dissipation corresponding to a specified damping coefficient. A method for calculating the damping of small amplitude surface waves in a circular tank was given by Case and Parkinson (1958). Viscous dissipation in laminar boundary layers was taken to be the primary cause of damping. Miles (1958) carried out an analysis of the effect of damping in an annular ring on the sloshing oscillations of liquid in a cylindrical tank. The effect of baffles has been considered more recently by Hamlin et al. (1986) and Armenio and Francescutto (1996a, 1996b).

ISOPE-I-00-257

The Tenth International Offshore and Polar Engineering Conference