Saeed Darvishi Alamouti - MS Student, University of Tehran;
Amir Davazdaemami - Master of Science, Sahel Consulting Engineers;

Evaluating hydrodynamic forces on marine structures is so important to design safe and reliable structure. One of the most important forces is wave force that should be considered in both constructing sequence and after construction stability analysis. Wave force on slender members can be calculated using Morrison equation but when the size of a structural body or member is sufficiently large diffraction theory should be used. In this paper wave forces on cylindrical members of the Persian Gulf Bridge are evaluated using both Morrison equation and diffraction theory andresults are compared. This paper also describes numerical method adopted in developing a program for modeling wave force on cylindrical members. The total wave forces are calculated with linear segments, but without the curve fitting technique. Numerical program written in MATLAB language is used for this purpose. Results show that diffraction theory predicts wave forces larger than Morrison equation (even 30% larger), because morison equation ignores the convective acceleration component in the inertia force calculation. It also ignores lift forces, slam forces, and axial Froude-Krylov forces.

diffraction theory, morison equation, wave force, cylindrical pile