Extraction of the second-order nonlinear response from model test data in random seas and comparison of the Gaussian and non-Gaussian models
This study presents the results of an extraction of the 2nd-order nonlinear responses
from model test data. Emphasis is given on the effects of assumptions made for the
Gaussian and non-Gaussian input on the estimation of the 2nd-order response, employing
the quadratic Volterra model.
The effects of sea severity and data length on the estimation of response are also
investigated at the same time. The data sets used in this study are surge forces on a fixed
barge, a surge motion of a compliant mini TLP (Tension Leg Platform), and surge forces
on a fixed and truncated column. Sea states are used from rough sea (Hs=3m) to high sea
(Hs=9m) for a barge case, very rough sea (Hs=3.9m) for a mini TLP, and phenomenal sea
(Hs=15m) for a truncated column.
After the estimation of the response functions, the outputs are reconstructed and the 2nd
order nonlinear responses are extracted with all the QTF distributed in the entire bifrequency
domain. The reconstituted time series are compared with the experiment in both
the time and frequency domains.
For the effects of data length on the estimation of the response functions, 3, 15, and 40-
hour data were investigated for a barge, but 3-hour data was used for a mini TLP and a
fixed and truncated column due to lack of long data.
The effects of sea severity on the estimation of the response functions are found in both
methods. The non-Gaussian method for estimation is more affected by data length than the
Advisor:Kim, Cheung H.; Powers, E.; Newton, H.J.; Kim, M.
School:Texas A&M University
School Location:USA - Texas
Source Type:Master's Thesis
Keywords:quadratic volterra model sea severity data length gaussian and non input nonlinear response tlp
Date of Publication:12/01/2004