International Journal of Coastal, Offshore and Environmental Engineering
Volume:3 Issue: 4, Autumn 2018

Three-dimensional numerical simulation of regular waves passing over cylindrical monopile has been conducted to investigate the hydrodynamic force and vortex dynamics. To do so, the rectangular wave flume and monopile is modeled on a solver; available in the open-source CFD toolkit OpenFOAM®. The solver applied RANS equations with VOF method for tracking free surface. Model validation has been done by comparison numerical results with the experimental ones and admissible agreement has been seen. Computations have been done for four cases with different wave characteristics consequently for different Keulegan-Carpenter numbers (KC). Hydrodynamic in-line force acting upon pile was studied and the results indicated that the total in-line force increases as KC number increases. In addition, when vortex shedding develops, drag force component increases and inertia force component decreases. The vortex dynamics around the pile was investigated by means of Q criterion and vorticity field. It was seen that by increasing KC number larger than 6, vortex shedding will be happened. Moreover, variation of bed shear stress around the pile has been investigated and it was seen that the bed shear stress is influenced by KC number which is result of existence of horseshoe vortices. The bed shear stress near the pile is negative due to existing of the horseshoe vortex. It begins when KC exceeds 6 and by increasing KC up to 20, the magnitude of negative values of bed shear stress near the pile increased which implies horse shoe vortices are completely formed. This also complies the experimental results.

In this study, the evolution and dependency of infragravity waves (IGWs) on wind waves for breaking and nonbreaking conditions is separately investigated. The efficiency of two constant cutoff frequencies (0.125 and 0.14 Hz) is compared for wave data measured in the sandy beaches of Nowshahr at the Southern Caspian Sea. It is found that the frequency of 0.125 Hz results higher correlation coefficients between IGWs energy content and two wind wave groups. Two pair different correlation patterns between IGWs in one side and wind waves higher and lower than 0.125 Hz in another side were recognized for breaking and nonbreaking conditions. In can be concluded that the IGWs excitation is controlled by the frequency distribution of wind wave energy.According to 0.125 Hz as more successful option, the correlation of IGWs with swell waves is generally more significant than sea waves. In the nonbreaking wave condition, the IGWs are well correlated with sea waves, whereas no considerable correlation between IGWs and sea waves is found in the breaking condition. It is resulted that IGWs energy is approximately linearly proportional of both swell and sea waves in nonbreaking condition. In the high and moderate energy incident wave conditions, the IGWs energy grows shoreward, while energy attenuation can be detected for IGWs in very low energy waves.

Hadish watercourse located in the in south of Iran, is a seasonal channel of water which crosses through Bandar Abbas to reach to the Persian Gulf. This watercourse is faced with numerous environmental problems in regard with the pollution entrance. Huge amount of the urban and industrial sewages of the city are discharged into this watercourse. In this investigation, considering the discharge of 1.36 m3/s into this watercourse, according to the literatures, the procedure of emission of pollution in the area was modeled. For this purpose Delft3D software has been employed. The model has been calibrated and evaluated considering water level data from Rajaee Port. It was found that, the pollution mainly remains inside the watercourse which is due to the ebb dominance nature of the channel. The results of this research show that the discharging the sewage into this channel endangers not only the western coast of Bandar Abbas, but the health of the citizens.

Desalination plants have become invaluable solutions especially where freshwater resources are scarce. However, the byproduct of their operation is an outflow which is more saline and heated than the ambient water body. This heated plume adversely affects the ecosystem if it is not treated properly. In this study, 3D finite volume coastal and ocean model is employed to address this issue close to Qeshm Island. In addition to calibrating the model, two alternatives are simulated and discussed to mitigate the adverse effects of the heated plume. It is shown that the plume tends to move in the upper layer of the water column due to its lower density than the ambient water. By moving the outfall to deeper parts of the sea—10-meter-deep—the negative effects of the plume significantly decreases and fulfilled the Iran national guidelines. Moreover, due to the mechanism of the Qeshm desalination plant, the spread of salinity is of the least importance compared to the increase in temperature.

Berm breakwaters are used as protective structures against the wave attack where larger quarry materials as armor stone is scarce, or large quarry materials are available but using berm breakwater lowers the costs considerably. In addition, wave overtopping in berm breakwaters are significantly lower than the traditional ones for equal crest level because of the wave energy dissipation on the berm.The most important design parameter of berm breakwaters is its seaward berm recession which has to be well estimated. In this paper a method has been developed to estimate the front slope recession of berm breakwaters using artificial neural networks with high accuracy. Four different available data-sets from four experimental tests are used to cover wide range of sea states and structural parameters. The network is trained and validated against this database of 1039 data. Comparisons is made between the ANN model and recent empirical formulae to show the preference of new ANN model.

Three-dimensional RANS simulations are employed numerically to study flow characteristics around a near-wall circular cylinder for varying gap-to-diameter (G/D) ratios (Where G is the gap between the cylinder and the wall and D is the cylinder diameter) and at Reynolds numbers from 100 to 3900. Pressure distribution around the circular cylinder, base pressure magnitude, separation and stagnation angles, force coefficients and Strouhal numbers were calculated and compared for all of the cases. Inception of vortex shedding can be seen when a sudden decrease in the maximum of positive pressure coefficient occurs. Vortex shedding mechanism and possibility of suppression further investigated via comparison of swirling strength in upper and lower vortex regions through parameter Λ, which signifies vortical activity and balance with respect to the wake center-line and also the flow type parameter, λ, representing the extensional strain dominance in the wake flow and gap flow. Vortex shedding suppression observed for the cases with the high unbalance vorticity content in the vortex regions, namely for Λ ≥ 2.