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ABSTRACT: An efficient and accurate numerical procedure is described for computing the second-order diffraction forces on arbitrary floating bodies in regular waves. Green" s second identity is exploited to express the second-order forces due to the second-order potential in terms of the first-order quantities alone. The resulting expressions for the second-order forces are evaluated from numerical first-order solutions based on the hybrid integral-equation method. The validity of the numerical procedure is confirmed by comparison of the computed results with the analytical solution for the second-order force on an articulated vertical cylinder. Results from the model tests on a circular dock are also presented to validate the theoretical predictions. INTRODUCTION The wave loads acting on floating structures in irregular seas include the second-order, high- and low-frequency force components at sum- and difference frequencies of the wave group, which arise from nonlinearities due to effects of finite wave elevation and finite body motions. These second-order forces may not be large in magnitude compared with first-order excitation at wave frequencies, but can never be ignored due to the possibilities of exciting resonance frequencies of lightly damped systems. Difference-frequency forces can excite large horizontal excursions of moored structures and large vertical-plane motions of floating structures of small water plane area. Sum-frequency forces can excite resonance oscillations in vertical modes of tension-leg plat-" forms. The prediction of the second-order forces on floating bodies is usually made on the basis of potential flow assumption. The forces can be obtained by integrating the hydrodynamic pressure over the submerged body surface and by retaining terms to second order in wave slope in a consistent perturbation expansion (Ogilvie, 1983). The resulting expressions for the second-order forces involve the contribution from the second-order velocity potential. To obtain this contribution, one may use two alternative approaches.
ABSTRACT: The world" s major fishing grounds are maintained by natural upwelling which enables nutrients in the sea water to rise from the seabed to the photic region and so increases primary production. The study reported here was concerned with the creation of new fishing grounds, where sea water upwelling will be generated by installing artificial ridges named "Super Ridge" on the seafloor, Coal ash, which has been used up until now to be disposed of mainly on reclaimed land is effectively utilized as the principal materials of these ridges This report outlines the "Super Ridge" project and discusses the technical problems involved in implementation of the project. 1. INTRODUCTION Japan faces the problem of decreases in catches on coastal fishing grounds due to restrictions on fishing within the 200 mile-zones in many countries and decreasing fishing resource due to water pollution from coastal reclamation and industrial effluent as well as overfishing. The situation calls for development of new coastal fishing grounds. At the same time, Japan, which is the second largest energy consumer in the world after the USA, is rapidly turning from oil to coal power generation to avoid becoming too dependent on a single energy source and thus ensure a stable energy supply. As a result the electric power output of coal-fired thermal power plants has already reached 13 GW as of 1989, and that level is expected to double within the next 10 years. Coal-fired thermal power plants produce coal ash at an annual rate of approximately 360,000 tons per 1 GW of power. which must somehow be disposed of At present, most of the coal ash is used as materials for reclamation of coastal areas. Although more effective uses for coal ash have been developed, there is no market for it in such large quantities.
- Materials > Metals & Mining > Coal (1.00)
- Energy > Power Industry (1.00)
- Energy > Coal (1.00)