Mahyar Pourlak - M.Sc. Member of Young Researchers Club, Islamic Azad University-South Tehran Branch, Tehran, Iran.
Hamidreza Rabiefar - Ph.D. Department of Civil Engineering, Islamic Azad University-South Tehran Branch, Tehran, Iran

The diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings, while the diffracted wave crests in the lee of the border will form approximately concentric circular arcs with the wave height decreasing exponentially along the crests. By using an appropriate CFD Software like DHI Mike21-BW Model (based on Boussinesq Wave theory) wave diffraction would easily be described and by describing and considering it in designing of project so many critical events such as earthquake and tsunami can be avoided.Wave spectrum is one of basic characteristics of any wave modeling, which changes the way of calculation of any wave numerical models. To assess the impacts that different wave spectrums cause on coastal regions, studies that evaluate the hydrodynamic behaviour and wave diffraction in sea water are necessary. A calibrated model is a suitable background for examination of these spectrums.In this paper by using this computer model and characteristics mentioned, the affection of the wave period change on the diffraction will be discussed. Meanwhile, for calibrating the model reputed Wave Diffraction Diagrams has been used, which will be discussed in appropriate section. It will be concluded Jonswap and Pierson-Moskovitz Spectrums has same behaviour in nodes near the breakwater opening; meanwhile Boussinesq wave Spectrum includes wider range of Cd quantity (Diffraction Coefficient) than the other spectrums.

Diffraction, Sensitive Analysis, Warm-up Period, MIKE 21, Boussinesq Wave Theory, Numerical Model