مجله علوم و فنون دریایی
سال بیست و یکم شماره 1 (بهار 1401)

In this study, sea level anomaly of Persian Gulf (spatial resolution of 0.25 degrees of latitudes and longitudes) was investigated in the MATLAB software environment by using long-term AVISO data for 25 years (1 January 1993 to 31 December 2017). The 25-year average of the data shows that the sea level anomaly is positive and equals 3.06 ± 0.05 cm (mean± standard deviation), which is higher than the global average. Its range varies from a minimum of 2.46 cm to a maximum of 3.42 cm. The 25-year average of each season illustrates that sea level anomalies face a rise in autumn and a fall in spring. The two seasons of summer and winter are transition seasons from the maximum anomaly of autumn to the minimum anomaly of spring. The results also show that the spatial distribution of sea level anomaly in the basin is different. The mean sea level anomaly trend in the Persian Gulf is +2.9±0.1 mm/year, which practically divides Persian Gulf in the three parts of northwestern parts near the Arabian coast (anomalies less than 2.5 mm/year), the northern and central parts of the gulf (anomalies of 2.5-5.5 mm/year) and the southern part of the gulf and Strait of Hormuz (anomalies more than 3.5 mm/year). Therefore, although the head of Persian Gulf has positive trend changes, it is less than its southern part and near the Strait of Hormuz. If the Persian Gulf Sea level continues to rise, over the next 200 years, the Persian Gulf sea level will rise more than 0.5 m, with significant changes in the size and area of the basin.

Plankton survey in coastal area of Southern Waters Qeshm was carried out in two season cold and warm and four stations (Parke Zeyton Beach, Soza Beach, Shibdraz Beach and Salakh Beach) during 2015 and 2016. In this study phytoplankton species belonging to 4 order Bacillariophyceae (Diatoms),Dinophyceae (Dinofellagelates), Chlorophyceae and Cyanophceae (blue-green algae) were identified. phytoplankton identification was done until genus and 31 ditoms, 11 from dinofllagelates, 6 from Chlorophyceae and 4 genus from cyanophyceae were identified.The mean (± SE) of density, biodiversity indices of Simpson,Pielo Shannon and Margalef were respectively 6705.72±63.9 Cell/L, 0.82±0.34,1.12±0.17 , 1.9±0.19, and 2.61±0.38 in season warm and 5666.13±53.2 Cell/L, 0.77±0.06, 1.12±0.11 , 1.9±0.17 and 2.26±0.43 in season cold.The seasonal similarity based on Sorensen's and Jaccard's coefficients were highest (0.97 and 0.88) for - two season warm and cold. In addition, there were significant correlation between Simpson and Shannon-Weiner diversity with salinity and PO4, and phytoplankton density with salinity and pH. A ccording to the results obtained can be concluded that both the area of ecological conditions in ranks are instead moderate. Also, phytoplankton of diversity and richness is good.

The design of oceanic numerical model for Persian Gulf to predict oceanic phenomena and parameters is one of the most important ways of preventing or solving problems environment and designing of the oceanic model similar to it is an effective method that can explain physical response of environment to different situations. Purpose of this research is designing oceanic numerical model for environment similar to Persian Gulf, to predict its reaction in return effect of tide and wind. This three-dimensional model based on primitive equations in spherical coordinates system with sigma vertical coordinate. To solve equations of model is used finite difference method. Compared with similar models, model framework and calculate more logical tension between are the benefits of this model. An oceanic five-layer basin is considered with maximum and minimum depth 100m and 80.09m. The average daily wind in Persian Gulf, the average daily salinity and water temperature and the changes in the water level in Strait of Hormuz are used in this model. The two-year implementation of model showed that in this basin, the tidal force is a dominant force compared with windy force and density gradient, also the maximum current in strait is 1.98 m/s which can create anticlockwise circulation in basin. Maximum total change of water height is 2.98 m in relation to the static level. Implementation results of this model correspond to the oceanographic reality of Persian Gulf, while matches with purpose; it is the basis of suitable model for Persian Gulf.

The prediction of ship resistance is the most important part of the ship's hydrodynamic design. Nowadays, computational methods are used as a common tool for this purpose. Ship total resistance calculation by using two phase numerical method based on the Reynolds-averaged Naiver–Stokes solution requires high computational power. The idea of total resistance decomposition based on the physical cause is a basic principle in the ship hydrodynamic. In the proposed hybrid method, wave making resistance part is calculated by using Michell Integral and viscous part is computed by numerical solution of one phase viscous flow for double body condition. Computations are performed for 10 velocities from Fn = 0.06-0.62 and at each velocity the percentage of every component calculated. Hybrid method reduce computational time.  To investigate the results, tow phase simulations are performed for a SWATH vessel. On average, there are 7% difference between the results obtained from hybrid and two phase method and computational time in hybrid method is 97% less than two phase method.

Sediment transport phenomenon is considered as one of the important and Effective factors in hydraulic performance and morphological structure of the coasts. In addition, stable development, engineering proceedings and the selection of the most appropriate protection method for organization and stabilization of the coast, are depends on the quantity of sediment load. Therefore, the focus of this study is generally to estimate sediment transport rate, assess the impact of coastal forest cover (Green Belt) on decreasing sediment transport rate exposed to tsunami wave trend and to obtain the parametric model to each coastal area using SPSS software. Experiments were performed on the effectiveness of a mangrove tree to reduce tsunami energy, by a simulated polyethylene synthetic shrub structure, for two rectangular and triangular tree layouts, 3 input wave height of 6, 9 and 12 cm, constant and horizontal slope of the coast, 0.35 mm sediment diameter and in terms of presence and absence of cover.. The results of this study show that despite forest cover, 41.17% of coastal erosion and scour are prevented and it helps to stabilization and restoration the coasts. Also considering conditions such as triangular layout selection and increasing cover density, 7.57% and 11.20% respectively, leading to the improvement of the coastal condition. Finally, the parametric model and the experimental equation for estimating the sediment transport rate with the correlation coefficient equal to 0.95, proposed as well.

The interest in bi-stable structures comes from their ability that these structures can have two different stable equilibrium configurations to define a discrete set of stable shapes. The geometrical changes occur with no need to continuously consume power, and mechanical hinges to preserve the structure in each stable shape. In this study, the stability characteristics and thermal response of a bistable composite plate with different asymmetric composition were considered. The non-linear finite element method (FEM) was utilized to determine the response of the laminate. Attention was focused on the temperature dependency of laminate mechanical properties, especially on the thermal expansion coefficients of the composite graphite-epoxy plate. Also the effect of including the resin layers on the stability characteristics of the laminate was investigated. The effect of the temperature on the laminate cured configurations in the range of 25°C to 180°C was examined. The results indicate that the coefficient of thermal expansions has a major effect on the cured shapes. Next, optical microscopy was used to characterize the laminate composition and for the first time the effect of including the resin layers on the actuation loads that causes snapping behavior between two stable shapes was studied. The results obtained from the finite element simulations were compared with experimental results and a good correlation was obtained.

One of the measures to control the hydraulic jump at the downstream of hydraulic structures and to provide required sequent depth is to use a stilling basin with sudden contraction. Previous studies have shown that in this basin the jump length increases compare to the classical jump. On the other hand, it has been shown that roughening the bed is a measure that can be used to decrease the jump length. Therefore, it can bring a question that by roughening the bed of sudden contraction stilling basin how much can decrease the jump length? Therefore, in this study the effect of roughness on jump length at the mentioned stilling basin has been investigated. The tests have performed in a flume of 12-meter-long, 0.8-meter-wide and 0.7-meter height. The contraction ratio was 0.33 and the Froude number ranged between 2 to 10. The results have shown that the roughness can decrease the jump length up to 31% compare to the classic jump and can decrease up to 12% compare to the smooth bed of sudden contraction stilling basin. The jump length is equal to the USBR type II. It was found that the roughness can decrease the roller jump up to 20 percent compare to the sudden contraction of smooth bed.