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Collaborating Authors
The Tenth International Offshore and Polar Engineering Conference
ABSTRACT If an ice sheet adfreezes to a structure with a circular cross section, such as the pile of a pier or a mooring pile, that is set in the water of a cold region, vertical ice loads acts on the structure if there is fluctuation in the water level due to the tide or other factors. Thus, the possibility of the occurrence 'of vertical ice loads must be considered when designing structure, s that will be subjected to ice loads. The vertical ice load acting on a single pile structure can be estimated by using the theoretical calculation method proposed by the authors. However, at present, there is no theoretical method for calculating vertical ice loads acting on a multi-leg structure. In the present study, field experiments were carried out for the first time on ice loads acting on multi-leg structures in an attempt to establish a theoretical method for calculating ice loads acting on such structures. INTRODUCTION The vertical ice load acting on a single pile structure can be estimated by the theoretical calculation method proposed by the authors Terashima et al. (1997, 1998), the accuracy of which was verified by their results of the first field experiments conducted on the uprooting of piles in a full-scale model. However, apart from the theoretical analysis performed by Kerr (1978) and laboratory experiments conducted by Christensen (1986), there have been almost no studies on vertical ice loads acting on the piles of a multileg structure. In the present study, therefore, field experiments were carried out for the first time on vertical ice loads acting on multi-leg structures in an attempt to establish a theoretical method for calculating ice loads acting on such structures.
- Asia > Japan (0.48)
- North America (0.47)
- Europe (0.46)
- Research Report > New Finding (0.65)
- Research Report > Experimental Study (0.51)
Abstract Flexural failure of ice on conical structures can produce a rubble pile or pile-up on the face of the cone. These features can increase the load significantly and affect the failure mechanism of the ice. Behaviour of rubble piles has been the subject of several ice tank programmes as well as limited programmes in the field. Using the data from the Confederation Bridge Monitoring Programme, observations pertaining to the rubble pile will be presented. The available video data allows for a continuous observation of rubble pile formation and behaviour and determination of the characteristics of the rubble pile. These characteristics include the size, shape, parent ice thickness, and piece size in the rubble pile, the effects of velocity, friction with the ice cover, and friction on the cone. The observations will be compared to existing theories on rubble pile formation and behaviour. Introduction Flexural failure of an ice sheet that interacts with a conical structure is one of several possible ice failure modes observed on offshore conical structures. Measurements and observations have shown that the highest loads occur when a significant rubble pile is present. Given the importance of the rubble pile, there have been several attempts to describe the behaviour of an ice rubble pile, some even with limited field observations. The Confederation Bridge Monitoring Programme (Brown et al. 1999) provides real-time data for ice interactions with the structure. The data from this programme is subject to a five-year confidentiality agreement that prevents publication of any specifics relating to the ice events. Using the data from the Confederation Bridge Monitoring Programme, a series of observations, both quantitative and qualitative, of sheet ice rubble piles have been made. The two primary quantitative observations relate the ice thickness and ice sheet velocity to the rubble pile height.
- North America > Canada (0.48)
- North America > United States (0.29)
Design And Cost Study of Gravity-Based Substructure In the Sea of Okhotsk
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.)
ABSTRACT 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. INTRODUCTION 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).
- Asia (1.00)
- North America > Canada > Ontario (0.28)
Numerical Analysis of Impulse Turbine For Wave Energy Conversion
Kim, Tae-Sik (Pukyong National University) | Lee, Hyeong-Gu (Pukyong National University) | Park, Ill-Kyoo (Pukyong National University) | Lee, Yeon-Won (Pukyong National University) | Kinoue, Yoichi (Saga University) | Setoguchi, Toshiaki (Saga University)
ABSTRACT This paper describes numerical analysis of the impulse turbine with fixed guide vanes, a high performance bi-directional air turbine having simple structure for wave energy conversion. A 2- dimensional incompressible viscous flow numerical analysis based on the full Reynolds-averaged Navier-Stokes equations was made to investigate the internal flow behavior. Numerical results are compared with experimental data obtained by T.Setoguchi. 6) As a result, a suitable choice of design factor has been clarified with the understanding of the internal flow from the numerical analysis. INTRODUCTION Of the several types of variable air turbines for wave energy conversion investigated, a Wells turbine has been widely applied for ocean-wave energy conversion mainly due to its simple structure at present. The wells turbine has however some inherent shortcomings; relatively lower efficiency, maintenance, higher axial thrust and noise in case of high power specification because the circumferential speed of rotor is essentially quite high 2) The impulse turbine with self-pitchcontrolled guide vanes has newly been proposed to overcome these drawbacks and have clarified that the turbine can be operated with higher turbine efficiency and lower rotational speed than those of Wells turbine. The type of impulse turbine with self-pitch-controlled guide vanes has a disadvantage of maintenance of pivots on which the guide vanes are rotated automatically in a bi-directional air flow and therefore, the authors have been investigated the impulse turbine with fixed guide vanes for the higher efficiency in the lower rotational speed than of more Wells turbine. In this study, so as to develop more practical turbine for wave energy conversion with simple structure, the numerical flow analysis was carried out to grasp the relationship between the characteristics of turbine and the internal flow structure of impulse turbine with fixed guide vanes under steady flow conditions.
Abstract The development of the wave energy converter Wave Dragon (WD) is presented. The WD is based on the overtopping principle. Initially a description of the WD is given. Then the development over time in terms of the various research and development projects working with the concept is described. This is followed by a description of the different parts of the structure together with a description of how this specific design has been chosen. Plans for the future development are finally presented. Introduction In recent years wave energy has gradually been brought into focus as it has become clear that fossil energy resources are limited and cause large environmental problems, e.g. CO2 pollution. In the light of this a number of different wave energy converters have been proposed. In Denmark the government decided to appropriate 40 mill. DKK (approx. 5.4 mill. EUR) to the development of wave energy devices during a period of four years, 1998–2001, and the European Union (EU) also supports the development through the JOULE program. Among the wave energy concepts receiving financial support from both programs is the WD. Presentation of the Wave Dragon The WD is a floating wave energy converter of the overtopping type. It is developed by Erik Friis-Madsen from the Danish engineering company Löwenmark Consulting Engineers. The WD can briefly be described as consisting of three components (see Figure 1, 2 and 3):Two wave reflectors for focusing the waves. A ramp leading the waves to the reservoir by overtopping. A number of low head turbines for converting the hydraulic head and flow into electricity. The main parts of each of the two wave reflectors are made of 12 equal straight elements. In addition, a longer element with less draught is attached at the end.
ABSTRACT Electric output characteristics of a new wave power conversion system are discussed. In this system, water valves, not mechanically operated, are combined with air chambers. The advantage of this system is that the rectifying water valves, with no moving parts, suffer less frequent failures. The demonstration test for practical use has been carrying out at Haramachi site since '96. The test plant consists of four air chambers, four water valve chambers, one turbine generator and so on. Air chambers are about 40m in length, 24m in breadth and 24m in height. The electricity, 130kW in specifications, is transmitted to the distribution line. In the demonstration test, we are measuring wave height, pressure in air chambers, water valve chambers and turbine room, electric output and so on. We obtained over 100 time series data from '96 to '98 on condition that the submerged depth of water valve is 10cm. In this paper, typical electric output data are shown and the relationships between sea condition and averaged or fluctuating electric output are discussed. We are planning to change the submerged depth of water valves and number of air chambers in the next phase of demonstration test. These plans are also discussed in the paper. INTRODUCTION Japan is a marine country of insularity surrounded by sea. The mean energy of the waves available at the Japanese seacoast is estimated to be about 6,4–7 kW/m, and the gross value of such energy is estimated to be about 13,400,000 kW(Sugawara, K. et al. 1986). The wave energy is of a low density, the fluctuation of which is high. However, it is clean and is one of those infinitely available.
- Energy > Renewable > Ocean Energy (1.00)
- Energy > Power Industry (1.00)
ABSTRACT A novel wave energy device (the 'Wave Rotor') is driven by the action of the Magnus effect on two parallel counter-rotating cylinders. This paper presents the results of experimental investigations of a model wave rotor both driven in still water and absorbing energy from incident waves, together with data on spinning cylinders in uniform steady flow and in waves. An estimate is made of the productivity of a full-scale device. INTRODUCTION The wave rotor (Retzler 1991) comprises cylinders that span between arms that turn about a central axis parallel with the wave crests (figure 1). Circulation in opposite senses around the two cylinders generates lift forces producing a moment about the central axis. In orbital flow the device rotates continuously at the wave frequency and power is extracted by providing damping to the rotation. Magnus lift forces on spinning cylinders in waves can be several times larger than the inertial forces depending on spin magnitude and wave size (Budal & Lillebekken 1985, Retzler 1987), offering the potential of a wave energy device of higher power for a given displacement. An earlier lift-driven wave energy device has been described by Hermans, van Sabben and Pinkster (1990). It used a foil, mounted on a shaft immersed in waves, which also performed full rotations synchronously with the waves. The device described here uses two cylinders for lift to give a couple around the centre of mass, hence requiring no counterbalance. Furthermore a spinning cylinder, unlike a foil, has no angle of attack and hence does not stall. EXPERIMENTS The wave flume The experiments were carried out in a wave flume 12.8m long, 0.425m wide, with a water depth of 0.7m. An electricallydriven absorbing wavemaker with force feedback generates waves over a frequency range of 0.5 – 2.0Hz.
ABSTRACT A Wells turbine has inherent disadvantages: lower efficiency and poorer starting characteristics. In this case, the guide vanes in front of and after rotor may be one of the most effective equipment for the improvement of the turbine performance. Several papers demonstrated the usefulness of 2D guide vanes so far. In order to achieve the further improvement of the performance of the Wells turbine, the effect of 3D guide vanes has been investigated experimentally by a model testing under steady flow conditions. And then, the running and starting characteristics under sinusoidally oscillating flow conditions have been obtained by a computer simulation using quasi-steady analysis. As a result, it is found that the running and starting characteristics of the Wells turbine with 3D guide vanes are superior to those with 2D guide vanes. INTRODUCTION Several of the wave energy devices currently studied in the United Kingdom, Japan, Portugal, India and other countries make use of the principle of the oscillating water-air column for converting wave energy to low-pneumatic energy which in turn can be converted into mechanical energy. In this case, the development of a bi-directional air turbine has come up as an important problem. So far, a number of self-rectifying air turbines with different configurations have been proposed, including the Wells turbine (Gato et al., 1988; Inoue et al., 1986a, 1986b; Kaneko et al., 1986; Raghunathan et al., 1987, 1994; Raghunathan, 1995; Setoguchi et al., 1986; Suzuki et al., 1985; White, 1995), a turbine using self-pitch-controlled blades (Raghunathan et al., 1997; Sannento et al., 1987, Takao et al., 1997), an impulse turbine with self-pitch-controlled guide vanes (Setoguchi et al., 1996), an impulse turbine with fixed guide vanes (Setoguchi et al., 1999) and so on (Kaneko et al., 1992).
The Offshore Floating Type Wave Power Device "Mighty Whale": Open Sea Tests
Washio, Y. (Japan Marine Science and Technology Center) | Osawa, H. (Japan Marine Science and Technology Center) | Nagata, Y. (Japan Marine Science and Technology Center) | Fujii, F. (Japan Marine Science and Technology Center) | Furuyama, H. (Japan Marine Science and Technology Center) | Fujita, T. (Japan Marine Science and Technology Center)
Abstract JAMSTEC completed the construction of the prototype device Mighty Whale by May 1998 for open sea tests to investigate practical use of wave energy. Following construction, the prototype was towed to the test location near the mouth of Gokasho Bay in Mie Prefecture. The open sea tests were begun in September 1998, after final positioning and mooring operations were completed. The tests are expected to continue for approximately 2 years. This paper presents an overview of the open sea tests, and summarizes the characteristics of power generation based on the results so far. Introduction JAMSTEC has been engaged in development of ocean-wave energy extraction technology for many years now. In particular, work began in 1987 on "Mighty Whale", which is a floating wave energy device based on the oscillating water column (OWC) principle. It converts wave energy into electric energy, and produces a relatively calm sea behind. This calm area can be utilized for varied applications such as fish farming. Theoretical investigations and model tests in 2 and 3 dimensional wave tanks led to an understanding of the hydrodynamic behavior of the device, and provided information that allowed safe and economical design of the prototype for open sea tests (Length 50m, Breadth 30rn, Depth 12m). Detailed design was completed in 1996. Construction began in January 1997 at the Ishikawajima Harima Heavy Industries Co., Ltd. (IHI) shipyard in Aioi City, Hyogo Prefecture. Prototype construction was completed by May 1998. Following construction, the prototype was towed to the test location near the mouth of Gokasho Bay in Mie Prefecture. Tests were begun in September 1998, after final positioning and mooring operations were completed. The experiments are expected to continue for approximately 2 years. Results are expected to provide a realistic understanding of the performance, safety, and economic features of the device.
- Energy > Renewable > Ocean Energy (1.00)
- Energy > Power Industry (1.00)
ABSTRACT Deepwater technologies available nowadays are based on the experience of installations, designs, and procedures for water depth up to 1000m. These technologies have been developed along the last twenty years. Today, the Ronrador and Marlim Sul Fields, the deeper fidds in Cmpos Basin Offshore Brmil, are located in water depth up to 2500m. The 3000m case is under evaluation. This demands new studies about equipment installation even when a dynamic pasidoning support vessel is used. This paper describes a dynamic response parametric study of a subsen tool installation suspended from a cable, in water depths up to JOOOm, using a Passive Heave Compensation System. Expedite procedure using a simplified model in frequency domain and simulations with non-linenr time domain analysis were performed in order to predict response amp|itnde and snap loading condition. This study is important to extend the present installation systems used such as Control Module, for example, that operate in 1000m to operate in up to 3000m water depth. A sensibility analysis changing dynamic excitation and Passive Heave Compensation System Configuration is also discussed. INTRODUCTION Rigs usually have heave compensation system which make them adequate for subsea equipment installation. However, the unavailability of these rigs has increased its daily rate. Basically, this is due to the deepwater activity that has been increasing throughout the world. Consequently, the use of a support vessel with dynamic positioning (DP) system has becoming inevitable to install subsea equipment mainly due to its low cost daily rate together with its availability in the international market. On the other hand, this option has some disadvantages, such as higher vertical amplitude motion. Subsea equipment installation by using a DP support vessel, changes the drill string philosophy to cable.
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Marlim Sul Field > Macae Formation (0.94)
- South America > Brazil > Rio de Janeiro > South Atlantic Ocean > Campos Basin > Marlim Sul Field > Lago Feia Formation (0.94)