عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Wave prediction is useful for safety and effective management of vessel navigation or construction of offshore structures. Since human activity mainly takes place in nearshore regions, accurate wave prediction is necessary there. However, nearshore waves are not easy to predict compared with ocean waves, because not only the waves but also the wind, which is the energy source of the waves, changes locally due to the complex terrain around the shore.
During the past 50 years, wave forecasting using numerical models according to wave energy balance equation has become widespread. These models also change significantly when new generation of spectral wave models such as Mike21-SW are suggested as the most advanced wave forecasting models. These models using formulation of basic physical wave generation by wind, wave transport and special processes of shallow waters e.g depth-induced wave breaking and bottom friction present reasonable results.
Shallow-water wave transformation strongly depends on coastal geomorphology and bottom sediment characteristics. Accurate prediction of wave parameters is vital for the coastal infrastructure developments and other activities. MIKE 21 SW is a new generation wind wave model based on unstructured meshes. The model simulates the growth, decay and transformation of wind generated waves and swell in offshore and coastal areas.
In this study, some semi-analytical methods and numerical model Mike21-SW at the Amir Abad port were wied to predict the wind wanes, with results that has strongest agreement with buoy data. To study and assess the semi-analytical method results, wave height and wave period are determined by SMB, SPM ,CEM, JONSWAP methods and compared with Amir Abad buoy data.Wind data which is used in semi-analytical methods are extracted from Babolsar synoptic station.
Because of the importance of Babolsar port, an unstructured application to the mesh file SW model was constructed covering 53.2 to 53.6 E and 36.8 to 37.2 N and mesh size in this area (which is uniform) is 0.005 degree( 500m). Boundaries in the north, east and west are open and in the south there is a closed boundary. The boundary condition of the local SW model is extracted as a parametric module from Iranian Sea Waves Modeling Project (ISWM) over 12 years from 1992 to 2004.These parameters are significant wave height, peak wave period, mean wave direction and spreading directional index.
Amir Abad buoy data was used for local SW model callibration. Comparsion which was made between the semi-analytical methods and buoy data shows that the SPM method has the best correlation with Amir Abad buoy data within the semi-analytical methods.
Over 12 years (from 1992 to 2004) wave climate in study area was assessed and compared with rose wave calculated by local model and with NEKA buoy data. Results shows that wave growth condition in Amir Abad area is a duration limited condition and only in few cases fully developed conditions occur.
In general , there is not good agreement between semi-analytical methods and buoy data and there is large error in using these methods. Semi-analytical methods predict values typically lower than observations.
Results show that the local SW model is the best method for wave condition prediction as is expected. Because in Local SW Model all phenomena associated with energy transport and with all frequencies and directions are included completely and any presupposition is not included.
The Root-Mean-Squired Error of SPM method in wave height forecasting is 0.45m, in wave period is 1.2 s . In semi-analytical methods, SPM method has good agreement in wave parameters forecasting.
The rose wave acquired by the local model indicates that dominant wave direction in Amir Abad Port is NW and another dominant wave direction is N.
Numerical model forecast for wave direction is more accurate than semi-
analytical methods and the wave rose acquired by the local model has good
agreement with the buoy data. The study suggests that another local model with
smaller mesh should be tried in this zone.