Random Wave Forces on a Free-to-Surge Vertical Cylinder
Abstract
The principal objective of this thesis is to gain insight into the applications and limitations of the relative motion form of the Morison equation for the prediction of hydrodynamic forces on a free-to-surge vertical cylinder in random waves. Force transfer coefficients are estimated from experimental data using regression with auto-regressive errors. The best fit relative motion form of the Morison equation results in a root-mean-square error of 24% and a multiple correlation coefficient of 0.71, over a 16 second time series. A high frequency force component not accounted for in the Morison equation is quantified. Cross-spectra are used to show that this residual force can not be duplicated by the relative motion Morison equation due to the lack of explicit history terms. A force transfer model containing explicit history terms is presented. The improvement in force prediction with increasing memory is illustrated and a memory length is chosen that optimizes the tradeoff between model complexity and goodness-of-fit. The new model reduces the rms error from 24% to 9%, increases the multiple correlation coefficient from 0.71 to 0.83, and captures the high frequency force components not accounted for in the Morison equation. A simple numerical simulation of a tension leg platform is performed to illustrate the application and limitations of the results.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1988
- Accession Number
- ADA198929
Entities
People
- Charles B. Sajonia
Organizations
- Texas A&M University