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- Numerical simulation of wave grouping effects on moored...
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UBC Theses and Dissertations
Numerical simulation of wave grouping effects on moored structures Pemmireddy, Venkata Rami Reddy
Abstract
The present thesis investigates wave grouping effects on the low-frequency drift force and the low-frequency surge response of a moored structure. The smoothed instantaneous wave energy history, SIWEH, which may be characterized by a number of parameters, is considered as an acceptable approach to describe wave groupiness. A numerical simulation of wave records is carried out for a specified wave spectral density and SIWEH incorporating various wave grouping parameters. The low-frequency drift force and the surge response of a large moored circular cylinder, modeled as a single degree of freedom system, is estimated on the basis of Pinkster's approximate method, which involves the use of computed drift force coefficients. Results show that the wave grouping parameters have a significant effect on the low-frequency drift force and surge response. It is also observed that the low-frequency drift force can be related to the SIWEH in terms of a transfer function. A statistical analysis of simulated low-frequency surge motions is performed, and the calculated extreme response is compared with the predictions of three theoretical models, namely the Gaussian, Exponential, and three-parameter methods. If the surge response has a non- Gaussian distribution, Stansberg's three-parameter model predicts extreme amplitudes reasonably well. The low-frequency drift force on a slender fixed circular cylinder is calculated using both Pinkster's approximate method and in the time domain using the Morison equation. Pinkster's approximate method underestimates the force, but it is computationally more efficient. The time domain approach is also used to estimate the low-frequency drift force on a moored slender circular cylinder and the results are compared to those for a fixed cylinder. It is observed that cylinder motion tends to reduce the drift force significantly.
Item Metadata
Title |
Numerical simulation of wave grouping effects on moored structures
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1992
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Description |
The present thesis investigates wave grouping effects on the low-frequency drift force and the
low-frequency surge response of a moored structure. The smoothed instantaneous wave energy
history, SIWEH, which may be characterized by a number of parameters, is considered as an
acceptable approach to describe wave groupiness. A numerical simulation of wave records is
carried out for a specified wave spectral density and SIWEH incorporating various wave grouping
parameters.
The low-frequency drift force and the surge response of a large moored circular cylinder,
modeled as a single degree of freedom system, is estimated on the basis of Pinkster's approximate
method, which involves the use of computed drift force coefficients. Results show that the wave
grouping parameters have a significant effect on the low-frequency drift force and surge response.
It is also observed that the low-frequency drift force can be related to the SIWEH in terms of a
transfer function. A statistical analysis of simulated low-frequency surge motions is performed,
and the calculated extreme response is compared with the predictions of three theoretical models,
namely the Gaussian, Exponential, and three-parameter methods. If the surge response has a non-
Gaussian distribution, Stansberg's three-parameter model predicts extreme amplitudes reasonably
well.
The low-frequency drift force on a slender fixed circular cylinder is calculated using both
Pinkster's approximate method and in the time domain using the Morison equation. Pinkster's
approximate method underestimates the force, but it is computationally more efficient. The time
domain approach is also used to estimate the low-frequency drift force on a moored slender circular
cylinder and the results are compared to those for a fixed cylinder. It is observed that cylinder
motion tends to reduce the drift force significantly.
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Extent |
3220617 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2008-12-17
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0050487
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1992-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.