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ABSTRACT This study is concerned with the motion measurements and human comfort on the floating structure in Japan "Sea Bus Terminal" in Yokohama Bay and "FLOATING ISLAND" in Setonaikai (Inside sea of Japan) are the representative examples on floating ocean structures used as the institutions for dwelling or leisure. Thus, the motion measurements and the questionnaire survey on human comfort for the visitors and the working staffs of Sea Bus Terminal have been performed In respect of the motion measurements, the accelerations on heave, surge and sway motion were measured. Moreover, two kinds of rotation angle on pitch and roll motions were dynamically measured. On the other hand, in respect of the questionnaire survey on human comfort, the main questions to the Visitors are about the degree of perception on motion, discomfort and uneasiness. In addition to the above questions, the period for the working staffs needing to experience on motion is included. Based on the comparative results of motion measurements and questionnaire survey, the relations between each motion and human comfort are discussed in this paper. INTRODUCTION Recently, the space utilizationin ocean which is one of the undeveloped area has been proposed in the various projects. The offshore or ocean structures are generally divided into two main categories, as known well, namely the fixed and floatmg type of offshore structures The greater part of floating ocean structures in Japan have been installed in coastal area and utilized as the tourist facilities Sakaigahama marine Park "FLOATING ISLAND" which has been utilized as a floating aquarium in Setonaikai (Inland sea of Japan) and Sea Bus Terminal in Yokohama Bay are the typical examples of existing floating structures. By the way, the stay of visitors and working staffs of such floating structures will be expected to become longer increasingly after this. However, there are only a few guides about the human comfort and reports about assessment of motion.
- Asia > Japan > Kantล > Kanagawa Prefecture > Yokohama (0.44)
- North America > United States > Texas (0.30)
ABSTRACT This study is concerned with the motion measurements and human comfort on the floating structure in Japan "Sea Bus Terminal" in Yokohama Bay and "FLOATING ISLAND" in Setonaikai (Inside sea of Japan) are the representative examples on floating ocean structures used as the institutions for dwelling or leisure. Thus, the motion measurements and the questionnaire survey on human comfort for the visitors and the working staffs of Sea Bus Terminal have been performed In respect of the motion measurements, the accelerations on heave, surge and sway motion were measured. Moreover, two kinds of rotation angle on pitch and roll motions were dynamically measured. On the other hand, in respect of the questionnaire survey on human comfort, the main questions to the Visitors are about the degree of perception on motion, discomfort and uneasiness. In addition to the above questions, the period for the working staffs needing to experience on motion is included. Based on the comparative results of motion measurements and questionnaire survey, the relations between each motion and human comfort are discussed in this paper. INTRODUCTION Recently, the space utilizationin ocean which is one of the undeveloped area has been proposedin the various projects. The offshore or ocean structures are generally divided into two main categories, as known well, namely the fixed and floatmg type of offshore structures The greater part of floating ocean structures in Japan have been installed in coastal area and utilized as the tourist facilities Sakaigahama marine Park "FLOATING ISLAND" which has been utilized as a floating aquarium in Setonaikai (Inland sea of Japan) and Sea Bus Terminal in Yokohama Bay are the typical examples of existing floating structures. By the way, the stay of visitors and working staffs of such floating structures will be expected to become longer increasingly after this. However, there are only a few guides about the human comfort and reports about assessment of motion.
ABSTRACT The guyed towers being compliant offshore systems have very low natural frequencies and therefore, are susceptible to low frequency excitation. Since second order drift forces in random sea have very low frequency contents, they may induce significant responses in the guyed towers. The time history of the drift forces is generated by using a simulation technique which obtains time histories of the square of the slowly varying wave envelope and instantaneous frequency dependent drift coefficients. The latter is determined from the mean viscous drift force acting on the tower for regular waves having different periods, combined with specified current velocity and mass transport velocity. The response of the guyed tower to random drift forces is determined in iterative frequency domain and the guylines are replaced by nonlinear springs whose force-displacement relationship is determined from a separate cable analysis. INTRODUCTION Offshore Guyed Tower platform belongs to the group of compliant offshore platform which is most suited for deep water search for all and gas. The basic feature of compliant offshore platform is that it is designed to move with the waves, in at least some of its degrees-of-freedom. As far as excitation at wave frequencies is concerned, the system opposes wave forces by inertial effects. This is in contrast to the fixed platform which opposes wave forces by stiffness effect in the structure foundation. Hence the fundamental natural frequency of a compliant system is designed to be well below the frequency range of waves having significant energy in the most extreme storm likely to be encountered. By their very nature, therefore compliant systems are susceptible to excitation at much lower frequencies than those of waves. Analysis of these structures for first order wave forces would then invariably predict very low responses.
ABSTRACT This paper is based on work conducted at the Offshore Technology Research Center to Investigate the relative importance of different types of nonlinearities on the dynamic response of tension leg platforms. A time domain solution using Monson's equation with several modifications and allowing to include or neglect various sources of nonlinearities was implemented and used in the dynamic analysis. This paper focuses on the nonlinear effect of evaluating the wave forces up to the free surface using different approximate methods. A TLP hull model with time varying tendon forces is subjected to regular and irregular waves with and without current. The effects on calculating the wave kinematics up to the mean water level or up to the actual free surface, making use of" various extrapolation or stretching techniques are then discussed. INTRODUCTION As oil exploration proceeds into deeper water, the tension leg platform is one viable and promising structural solution. The characteristics of the TLPs are quite challenging and interesting at the same time. Despite the considerable amount of work which has already been done to understand their behavior, there is still a great deal more research which is required. A TLP can be modeled as a six degree of freedom system. The natural frequencies in surge, sway and yaw are well below the range of wave frequencies. On the other hand, the heave, pitch and roll natural frequencies are above the exciting wave frequencies. There are thus two different nonlinear aspects which need to be considered m the design of TLPs, one related to the amount of offset permitted, the other to the limits (i.e. minimum and maximum) of the tendon tension forces. The former is mainly influenced by the slowly varying drift forces (low frequency response) while the latter is greatly affected by the springing and ringing phenomena associated with high frequency response.
- Europe (0.68)
- North America > United States > Texas (0.46)
ABSTRACT Thus paper describes the development and implementation of a typical variable Amplitude load sequence on tethers for a tension leg platform. The dynamic Response of the Hutton TLP was considered m defining a suitable tether tension Response spectrum. This spectrum was then used to generate a time series to Give a similar amplitude-frequency distribution. Two full scale variable Amplitude fatigue tests on large diameter threaded connections are reported Using the simulated load sequence the fatigue test results are compared with Constant amplitude results from a previous study on similar connections A hybrid electric analogue-finite element technique was used to determine The local stress at the critically loaded tooth from which all failures were Initiated. Fracture mechanics analysis of the critical cracks was conducted Using a recently developed generic weight function solution for threaded Connections crack aspect ratio was also considered together with previous Related studies in all, the paper presents useful fatigue crack growth data and Analysis of threaded tether connections under realistic simulated service Loading. INTRODUCTION A Tension Leg Platform (TLP), or Tension Buoyant Platform (TBP), is a floating structure having a novel mooring system. The platform is held against Its natural buoyancy by a number of vertical risers fixed to the sea bed these risers consist of clusters of tethers which are generally loaded axially in tension. Wave and wind loading on the installation cause the tethers to be randomly stressed. The degrees of freedom of such a structure are shown 10 Fig 1. The Hutton TLP (1984) was the first platform having its tether segments connected by threaded fasteners this pioneering project raised many technical problems requiring inventive solutions service data of how successful these have been is only now becoming available and much analysis is required to understand the service load mechanisms acting on the structural components of the platform.
ABSTRACT Research and development of the Tension Leg Platform (TLP) have been performed in the "Offshore Oil & Gas Production Platform Project" of Japan Ocean Industries Association (JOIA) promoted by the Ministry of International Trade and Industry, Japan (MITI). In this project, the tendons that are planned to be fabricated and assembled on the land in an overall length will be horizontally towed to the site. After that, they will be installed there. The towing procedure, however, has been established neither theoretically nor empirically Therefore, the on-site experiment was performed to investigate whether it is possible to plan the towing procedure at the sea. The bending moment and the towing force of the tendon model during the towing procedure were measured. INTRODUCTION Recently, the tension leg platform (TLP) continues to be a leading concept for petroleum production in deep water. Many kinds of projects and concepts of the TLP are presented. Some types of the tendons are also presented in these projects. One of the most promising type of the tendons is a light weight and pre-fabricated tendons. In the concepts using the light weight tendon, the thickness and the outside diameter can be selected to obtain tine neutral buoyancy. This type of the tendons can increase the deck carrying capacity. If the light weight tendons are fabricated by the welding process in their overall length on the land, the cost for the fabrication and the time for the installation are decreased in comparison with the tendons that are connected by the thread joint at the site. The behavior of these tendons is investigated not only the strength in the working condition but also the method in the towing condition and the installation (Wybro, 1990, Morikawa, 1991a, Morikawa, 1991b, Morikawa, 1992. Ishikawa, 1992). In fact, the sinking of the first four of the TLWP's 12 mooring tendons during tow-out is well known.
ABSTRACT This paper presents a result of an analysis of the nonlinear Interaction and response of the coupled ISSC-TLP System to the random seas In the time domain The environmental load also includes the effect of the concurrent steady winds and currents. The first- and second-order wave-exciting forces are calculated using a robust higher-order boundary element method (HOBEM), while the nonlinear tendon dynamic analysis is performed using the three-dimensional hybrid element method with the updated Lagrangian formulation. The Monson equation is employed for the wave and current load on slender structures The analysis is focused on the nonlinear responses due to the nonlinear environmental load and nonlinear interaction between the platform and tendons that Includes the offset, setdown, large coupled surge-heave motion In the low frequency and Resonant heave/pitch responses with the springing loads In the high Frequency. INTRODUCTION This paper presents an analysis of the nonlinear interactions and responses of the coupled ISSC-TLP In the long-crested random seas m concurrence with the steady action of the wind and current The TLP system is a compliant platform whose mooring system has soft lateral and stiff vertical restoring forces, which create the lateral and vertical mode resonance motions m the low and high frequencies, respectively. The responses of the TLP system near the resonance frequencies are activated by the second-order nonlinear wave exciting forces. The nonlinear lateral environmental load induces a large drifting oscillation and brings the platform to Its mean drifted position (offset) and the setdown of the platform. The TLP system then oscillates around the mean shifted position. Under the circumstances, the tendons may non-linearly respond due to its large geometrical displacement the heave/pitch resonant motions induce the springing tension loads m the tendons which are Important for the fatigue estimate.
ABSTRACT The Hibernia offshore 011 platform IS the first major platform for the development of hydrocarbon reserves on the Grand Banks off the East Coast of Canada. The platform, a concrete gravity base structure supporting 60,000 tones of topsides, Will be In 80 m of water and IS designed to resist Iceberg collisions The paper describes the platform, environment and Iceberg loads, geotechnical considerations and the structural analysis being performed. The platform IS currently under construction (Winter 1993) and Will be completed In 1996. INTRODUCTION The Hibernia 011 Field IS located 315 km east-southeast of St. John's, Newfoundland, Canada (Fig. 1) It was discovered In 1979 Recoverable reserves are contained In two reservoirs and are estimated at 615 million barrels. Partners In the Hibernia Field are Mobil 011 Canada, Chevron, PetroCanada, Murphy 011 and the Canadian Government. The project IS being conducted on behalf of the Partners by a specially formed operating company, the Hibernia Management and Development Company (HMDC). The platform selected to develop the Hibernia reserves IS a concrete gravity base structure (GBS) which Will be located on the Grand Banks In 80 m of water. The Hlberf1la GBS (Fig. 2) IS the first large offshore concrete platform to be built In North America although many small concrete platforms have been built In the Gulf of Mexico since the early 1950's (1) This paper concentrates on the gravity base portion of the platform. Reference to the Topsides is added for clarity. The information presented represents the status of the platform as of the beginning of 1994. The Hibernia gravity base structure (GBS) IS essentially a cylindrical concrete caisson that extends from the seabed to 5 m above the waterline (Fig 3).
- North America > Canada > Newfoundland and Labrador > Newfoundland > St. John's (0.34)
- North America > Canada > Newfoundland and Labrador > Newfoundland > North Atlantic Ocean (0.24)
- North America > Canada > Newfoundland and Labrador > Newfoundland > North Atlantic Ocean > Atlantic Margin Basin > Grand Banks Basin > Jeanne d'Arc Basin > Hibernia Field > Hibernia Formation (0.99)
- North America > Canada > Newfoundland and Labrador > Newfoundland > North Atlantic Ocean > Atlantic Margin Basin > Grand Banks Basin > Jeanne d'Arc Basin > Hibernia Field > Avalon Formation (0.99)
ABSTRACT Ridge transitability is one of the most important features of a ship navigating through the polar sea. This paper reviews the general tendency of polar ships, and describes a rational method for determining the installed horsepower that allows continuous icebreaking mode in a ridge fled, using calculation technique based on the model test results of iceload and speed loss measured while transiting through model ridges. INTRODUCTION Polar technologies have been promoted in various countries, aiming at exploration of natural resources, development of a northern sea route of Russia, scientific research around the Antarctica, etc. These R&D necessitate development of polar ships such as icebreakers for breakout of ice sea and observation support and icebreaking tankers for transportation of natural resources. For this purpose, studies of icebreaking performance in various ice conditions have been conducted by many searchers since the 1970'. However, as the Arctic ice conditions are multifarious among different places and different times, it is hard to indiscriminately determine design conditions of polar ships as in ordinary ocean gong ships. Kinds of ice (level ice, ridge ice field, and snow covered ice) and frequency of such ice kinds are vital factors in determining the hull form and the main engine horsepower of polar ships. This paper deals with the above problem from aspect of the ridge transit performance. First, the tendency and change of principal particulars of typical polar ships bullet In the past are reviewed, taking account of hull form parameters which govern the icebreaking performance. Then, the icebreaking performance of a self-propelled icebreaking tanker - that is, the ridge field transit performance which is most important in the icebreaking ability of this kind of ship - and the way of determining the required main engine horsepower based on this performance, are discussed as follows:
- Asia (0.89)
- North America > United States > Louisiana (0.24)
- North America > United States > Colorado > Cheyenne County (0.24)
ABSTRACT A systematic analysis of effects of compressibility of water on hydrodynamic behaviour of axisymmetrical subsea storage tanks has been carried out, using a Hybrid element method in frequency domain. Including the compressibility of water, provides physically, hydrodynamic damping at higher frequencies and it has got substantial influence on added mass distribution and on hydrodynamic pressure distribution. The specific contribution of this study is that for certain frequencies of excitation the added mass for subsea structures becomes negative. The - variation of hydrodynamic pressure, added mass and hydrodynamic damping coefficient with respect to the frequencies are presented. The results and conclusion would be useful for proper dimensioning of the tanks for efficient functioning. INTRODUCTION It has been forecast that about 80% of future production of oil from North sea and worldwide would be from small and marginal fields, i.e. fields of 100 million barrels of recoverable reserves and less. For such fields the early production system and subsea systems are more advantageous from economical and technological factors. continuity in production can be maintained if an offshore storage facility is available. Offshore storage enables the production to continue during interruptions in offloading of the export crude oil. Interruptions do occur when shuttle tankers are used for transport and also when the submarine pipeline is shut down for maintenance. The economic benefits of an offshore storage are essentially those from maintaining the continuity of production. For offshore platforms like Gravity platforms the offshore storage is provided at the base of the platform in the caissons. In early production systems and subsea systems the storage has to be provided on floating unit or on subsea storage tanks. The subsea storage tanks are wholly submerged in the sea and have no net buoyancy so that they remain supported by the sea bed.
- North America > United States (0.47)
- Asia > Japan (0.28)
- Europe > United Kingdom > North Sea (0.24)
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