M. Naghipour - , University of Mazandaran

This paper describes the various frequency domain methods which may be used to analyze experiments data on the force experienced by a circular cylinder in wave and current to estimate drag and inertia coefficients for use in Morison’s equation. An additional approach, system identification techniques (SIT) is also introduced. A set of data obtained from experiments on heavily roughened circular cylinders in waves and simulated current has been analyzed by all these techniques. The resulting force coefficients are then used to predict the force from separate experiments-results, which have not used in the analysis. The root mean square error and bias in the estimation of maximum force in each wave cycle is used a measure of predictive accuracy and as a basis for comparing the analysis techniques. The case when wave particle kinematics must be inferred from water surface elevation is also considered. It is found that when water particle kinematics are not possible to be measured directly and have to be inferred from surface elevation then using a system identification approach, the predictive errors increase considerably.

Morison’s Equation, System Identification Techniques, Stokes Theory, Wave Reflection, Particle Kinematics