Abstract
The responses of an articulated loading platform (ALP) in regular and irregular unidirectional waves (with or without currents) are investigated both in frequency and time domain. The first- and second-order wave diffraction radiation are solved by the ring source boundary integral equation method, and the viscous drag forces are computed from the modified Morison equation. The two-term Volterra series and linearized drag force model are used for the spectral analyses in frequency domain, while the fourth-order Runge-Kutta method is used for the time-domain integration of the nonlinear equation of motion. It is shown that the linear wave-body interaction theory combined with the linearized drag model appears to be satisfactory in computing wave- frequency responses in regular and irregular waves. However, the natural frequency of the ALP pitch motion is typically small, thus the linear theory alone is not adequate to evaluate the resonant slowly-varying pitch responses in random seas, for which the second-order difference-frequency wave loads play the most important role. These low-frequency responses can be greater than the wave-frequency responses depending on the available damping, hence need to be included for the reliable motion analyses of an ALP. Finally, the current effects on the response of the ALP are also investigated. It is seen that the presence of currents significantly increases the mean pitch angle, while tends to decrease both wave- and low-frequency dynamic responses.
Ran, Zhihuang (1993). Responses of an articulated loading platform in waves and currents. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1993 -THESIS -R185.