عنوان مقاله [English]
In this paper the effects of permeable bed on wave run up, bed shear stress and internal currents inside the bed, the shape of streamlines and trajectories of fluid elements inside the bed are studied.
The experiments have been done in Hydraulic Laboratories of Sea and Coast in “Soil Conservation and Watershed Management Research Center”.
General properties of flow in rivers, estuaries, and coastal seas are highly dependent on the bed morphology. These include mainly bed shear stress, velocity profile, and turbulence.
We consider the effects of suction (W>0) and injection (W<0) on the properties of flow, particularly the bottom shear stress. Four types of bottom perm abilities with different size of sand have been tested. The results indicate a substantial reduction and enhancement of the bed stress under injection and suction respectively as has been observed by others on wave motion in shallow seas. For this study we considered 5 groups of waves oncoming to shore in the steepness ranges between 0.015 and 0.05. Observations of streamlines inside the bed were taken using a video camera embedded inside the bed, which recorded the pattern of injected dye. Speed of current is computed in two locations: 3 and 13 cm depth by introducing V = W / U (relative dimensionless suctions/injection velocity) we found that for the suctions case, when V increases, the stress are enhanced. While for injection case (V1) , the stress is reduced. Typically, t/ t0varies between 2.5 for Vs= -0.4. Hence, relative bed stress can vary by a factor of 5 which can have a substantial impact on the bed morphology.