Yungang Liu - Academia.edu (original) (raw)
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Papers by Yungang Liu
Marine Structures, 1999
A new procedure is proposed to generate a slowly varying drift force (SVDF) time series for moore... more A new procedure is proposed to generate a slowly varying drift force (SVDF) time series for moored floating platforms. The idea is to pass a random signal through a filter, the filter coefficients are determined from the SVDF spectrum, and the random signal follows the theoretical probability distribution function of the SVDF. The primary benefits of using such a procedure are that arbitrarily long SVDF time records can be generated; and the problems associated with adding a finite number of sine waves with deterministic amplitudes can be avoided.
Engineering Structures, 1997
A linear, frequency-domain, dynamic method is introduced to calculate large motions of slender st... more A linear, frequency-domain, dynamic method is introduced to calculate large motions of slender structures such as towing and mooring cables, and flexible risers. The viscous, drag damping is linearized at element level by calculating linearized equivalent damping coefficients through iteration. In the introduced method the work done by the motion of the cable in the time domain is equated with that done in the frequency domain. The linearized, frequency-domain results are compared with results from nonlinear simulations for a towing cable, a mooring line and a lazy-wave riser. The influences of excitation frequency and excitation amplitude are considered.
Applied Ocean Research, 1999
One special feature in moored floating platforms is the co-existence of the first-order wave-freq... more One special feature in moored floating platforms is the co-existence of the first-order wave-frequency (WF) response and the second-order low-frequency (LF) resonant response. Non-linear properties inherent in moored floating platforms cause the platform motions and mooring cable tensions to be non-Gaussian (not normal) distributed, both for the WF and for the LF components. As the LF and the WF components are not independent, it is important and necessary to find a simple, reliable and yet physically sound technique to estimate their combination. In this paper, on the basis of some model test results, different combination formulae are compared and a formula considering WF and LF correlation effects is suggested. A simple approach is also proposed to estimate the correlation factor.
Marine Structures, 1999
A new procedure is proposed to generate a slowly varying drift force (SVDF) time series for moore... more A new procedure is proposed to generate a slowly varying drift force (SVDF) time series for moored floating platforms. The idea is to pass a random signal through a filter, the filter coefficients are determined from the SVDF spectrum, and the random signal follows the theoretical probability distribution function of the SVDF. The primary benefits of using such a procedure are that arbitrarily long SVDF time records can be generated; and the problems associated with adding a finite number of sine waves with deterministic amplitudes can be avoided.
Engineering Structures, 1997
A linear, frequency-domain, dynamic method is introduced to calculate large motions of slender st... more A linear, frequency-domain, dynamic method is introduced to calculate large motions of slender structures such as towing and mooring cables, and flexible risers. The viscous, drag damping is linearized at element level by calculating linearized equivalent damping coefficients through iteration. In the introduced method the work done by the motion of the cable in the time domain is equated with that done in the frequency domain. The linearized, frequency-domain results are compared with results from nonlinear simulations for a towing cable, a mooring line and a lazy-wave riser. The influences of excitation frequency and excitation amplitude are considered.
Applied Ocean Research, 1999
One special feature in moored floating platforms is the co-existence of the first-order wave-freq... more One special feature in moored floating platforms is the co-existence of the first-order wave-frequency (WF) response and the second-order low-frequency (LF) resonant response. Non-linear properties inherent in moored floating platforms cause the platform motions and mooring cable tensions to be non-Gaussian (not normal) distributed, both for the WF and for the LF components. As the LF and the WF components are not independent, it is important and necessary to find a simple, reliable and yet physically sound technique to estimate their combination. In this paper, on the basis of some model test results, different combination formulae are compared and a formula considering WF and LF correlation effects is suggested. A simple approach is also proposed to estimate the correlation factor.