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Discuss the Hydrodynamics and Mooring System of a New Type Wave Buoy

Author: ChenChangLong
Tutor: YangYongChun
School: Ocean University of China
Course: Port, Coastal and Offshore Engineering
Keywords: measurement of wave direction model test Fiber Bragg Grating distribution of tensile forces
CLC: P715.2
Type: Master's thesis
Year: 2010
Downloads: 72
Quote: 0
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Abstract


Ocean data buoy is mainly applied to measure parameters of marine hydrology and meteorology. Wave parameters which include wave height, wave period and wave direction is an important part of the hydrological factors measurement. As an important parameter, wave direction is widely used in ocean engineering and oceanic prediction. The method of measuring wave direction based on acceleration transducers becomes a new topic in the study at home and abroad. This method is based on the wave buoy’s characteristics of horizontal motion in wave to determine the wave direction, primarily based on the horizontal acceleration response. In this paper we design a non-contacted system of measuring horizontal motion to verify the reliability of this method. Then we carry out the model test, study the relationship between horizontal movement of the buoy and wave direction, providing a reference for the wave direction measurement.A traditional method to determine the tensile forces in the mooring line of offshore structures in model test is to place a load cell at its top end. Only the tensile forces in the top of the mooring line are obtained, but tensile forces in other positions are unknown. The invert S mooring system of deep water challenges the existing testing method of tensile force. It is noted that for some floating structures the distribution of tensile forces along the length of the mooring line is an essential factor for engineers to consider, based on which the ultimate limit state and serviceability limit state can be checked. Therefore, there is a need to propose a test method to examine the forces in various positions of the mooring line, and to verify the traditional numerical methods using obtained test data. This paper presents a new test method based on Fiber Bragg Grating technology. According to this method, one optical fiber with Bragg Gratings are put inside the mooring line in pre-determined positions, and tensile forces in those positions are obtained in the test. The distribution of tensile forces along the length of the mooring line can thus be determined. This method was employed in the buoy model test conducted by the authors, and demonstrated reasonable accuracy. Compared with the traditional test method, the proposed one eliminates the hydrodynamic effects of the mooring line by traditional load cells, which are normally heavier and bigger than the fibers. Moreover, real-time distribution of tensile forces in the mooring line can be obtained using the proposed method. It can be concluded that this method may be widely used in the model test of moored offshore structures.

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CLC: > Astronomy,Earth Sciences > Oceanography > Marine survey and observation > Investigation and observation equipment > Buoyage
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