نشریه هیدروفیزیک
سال هشتم شماره 1 (پیاپی 14، بهار و تابستان 1401)

In this study, the wave-induced force acting on stepped-face porous seawalls was investigated experimentally using physical modeling. Regular waves in a wide range of heights and intervals were investigated. Tests were carried out for a constant water depth of 0.375m and for different inclinations of porous seawall (i.e. θ = 90, 75, 60 and 45 ̊). It was inferred that the factors of relative water depth, wave steepness, the slope of seawall and the surf similarity parameter were effective in predicting the maximum wave force (Fm). The values of Fm for stepped-face seawalls ranged from 3.8–12.8N, and for the vertical porous seawall it was 4.1–16.7N. Comparison the measured values of Fm for different seawalls revealed that the wave-induced forces acting on the stepped-face walls were heavier than the vertical porous wall about 18%. Therefore, the stepped-face seawalls have a better performance compared with the vertical wall in absorbing and dissipating wave energy. Based on the measured data, dimensional analysis and nonlinear regression analysis, new empirical relations are proposed to predict the maximum wave force. These findings were calibrated using SPSS based on the experimental results. The findings of the present investigation can be applied to optimize the design criteria of sloped seawalls for shore protection from erosion.

Eddies formation is an important oceanic phenomenon that plays a significant role in the transport of fluid in the ocean. The main eddy in the Persian Gulf is mainly due to factors such as wind, tide and density variations. This paper uses the HD model of MIKE3D packages to perform the simulations; first a large-scale flow model is implemented for the entire area of the Oman Sea and the Persian Gulf, and then the formation of mesoscale in the Persian Gulf and the Oman Sea is simulated by the output of Model 3 MIKE with a resolution of ten kilometers for 2013 in 30 layers of Sigma and Z coordinates. Almost all year round, a thermohaline stream enters the Oman Sea Persian Gulf and penetrates deeper areas, causing fluctuations in the temperature and salinity in the Oman Sea. This thermohaline flow that enters the Oman Sea causes temperature changes and these changes cause the formation of eddy in the Oman Sea. It was also seen that a coastal stream in the northwest direction from the north of the Strait of Hormuz enters the Persian Gulf and there is a southwest stream in the southern part of the strait. The main eddy in the Persian Gulf is clockwise and it was observed that the general shape of the eddy in the Persian Gulf is clockwise and the counterclockwise eddy in the center of the Persian Gulf becomes stronger from April to July and in August, it has the highest resolution. In this study, more attention was paid to the months when eddy has more clarity.

Predicting factors like height and frequency of the waves in seas is one of the most essential information needed in the marine environment. In the present paper, the height of the waves in the Gulf of Mexico were analyzed by transforming wavelet into different sub-levels of approximation and details; and the wave height of the upcoming 3, 6, 8 and 12 hours lead time was predicted by artificial neural network. By comparing the real data measured by Buoy with the results of neural network prediction, it was found that coif(5) with 5 subsurface for 3 lead times and 6 Dmey wavelets with 6 and 7 subsurface are appropriate for predicting wave heights for 6, 8 and 12 lead times respectively. Then the meteorological parameters of air pressure, air and water temperature variation, wind direction, and wind speed were also added as model inputs. With this method, it was inferred that the parameters of wind direction and the variation in air and water temperature have no effect on the forecast accuracy. And by adding the current recorded wind speed and air pressure, the forecast accuracy increased compared to the case where only the decomposed subsurface was used. Finally, the predicted values of wave height at the time of the occurrence of Hermine, Choline and Matthew hurricanes in 2016 were evaluated and the results showed that at the time of the occurrence of Hermine and Choline hurricanes, the prediction accuracy of the model was significantly reduced.

Measuring the concentration of sediments on beaches is of particular importance in line with the implementation of beach management plans. Coastal currents, especially those caused by breaking waves on the intermediate beaches, are considered one of the most important phenomena in the sediments transport and pollutant emissions in seas and coastal environments. In this research, first the complex pattern of these currents was implemented in beaches with an intermediate state in laboratory conditions. Then, using the governing empirical formulas, the concentration of sediments in each run was calculated under the sediment suspension mechanism due to the turbulent movement caused by broken waves. In the next step, using image processing principles in the Matlab software, the color characteristics of the images at different depths and hydrodynamic conditions were extracted to estimate the surface Suspended Sediment Concentration. The main results of this research show the high correlation of the color features of the images with the concentration of sediments in the area based on the algorithms presented in the RGB and Grayscale models. The accuracy of the results presented in different parts of the near shore zone indicates the fact that the accuracy of the model results decreases by moving towards the beach face and the best fit of the features of the images and the amount of sediment concentration is seen in the shoaling region.

In this research, the optimization of the geometric parameters of the hovercraft skirt is investigated using the PSO algorithm in order to reduce the range of vibrations on the structure and increase the ride quality. At first, the dynamic equations governing the hovercraft in two states of contact with the ground surface and non-contact are presented. Based on the presented nonlinear dynamic equations, the equilibrium point of the hovercraft was extracted and by linearizing the nonlinear dynamic equations governing the heave motion of the vessel around the equilibrium point, the linear form of the governing dynamic equations was extracted. In order to reduce the vibrations and increase the ride quality with the vessel, an objective function is presented, and based on this objective function and using both forms of linear and non-linear dynamic equations, the geometric parameters of the skirt are obtained based on the intelligent PSO algorithm. Finally, it is shown that comparing the frequency and time behavior of the optimized hovercraft with the original hovercraft, the range of vibrations is reduced and the ride quality with the optimized hovercraft is greatly improved.

The issue of preparedness and security against unexpected events is so important in today's world that developed countries devote an important part of their comprehensive national planning to it. Population growth, agricultural water demand, and climate change increase the likelihood of water shortages. Flood is one of the most common natural disasters that brings significant impacts and damages to water supply. Therefore, checking the water supply chain is a necessary demand, and delaying it causes instability and vulnerability to natural and human crises. The purpose of this research is to study the flood threat on the water supply process. This applied study uses an integrated approach (qualitative and quantitative) to achieve its purposes. In the qualitative phase, theoretical literature review and interviews with experts are discussed. The sampling method was purposeful and 14 environmental management professors and water experts were selected. In the quantitative phase, a non-probability sampling method was used and 230 employees and workers of the water and sewage company of Gilan province answered the questionnaire. MAXQDA 2020 software was used in the qualitative method. Also in the quantitative method, the data were analyzed with the structural modeling approach and partial least squares method. The results of the analysis showed that there are positive and significant coefficients between the hidden variables (improvement, preventing arbitrary construction, primary control and assessment, provision of reserve facilities and coping facilities) and the flood threat.