نشریه هیدروفیزیک
سال هفتم شماره 1 (پیاپی 12، بهار و تابستان 1400)

The waves affect the vertical movements of the vessels, thereby endangering the safety of their movement in coastal waters. This study has been conducted to accurate wave prediction in the shipping channel of Bushehr port in order to ensure safe and efficient maritime transportation of this region. First, the wave simulation was performed using PMODynamicsI software and using GFS predictable wind field. By applying the optimal settings in the model and comparing the model results with the wave measured values at the shipping channel location, the accuracy of the verification results was equal to 70%. The results showed that the use of large-scale and global wind caused a decrease in modeled wave height and lack of proper accuracy in wave direction simulation during the occurrence of storms with a sudden change of direction, which due to the importance of maritime safety discussion, accurately prediction of the wave by using predictable local wind has been considered. This has been done through artificial neural network technique and design of different scenarios, which has generated wind with local precision by training the GFS global wind field through meteorological wind data. This wind has been used in Bushehr wave model, which has led to a 20% and 15% increase in accuracy for the direction and height of the modeled wave, and a 10% decrease in the root mean square error.

Nowadays, one of the methods of aquifer quality management is the assessment of aquifer pollution potential, based on which, aquifer quality can be determined and appropriate management can be applied to aquifer lands. Therefore, aquifer vulnerability assessment is an important part of water resources management. The aim of this study is to evaluate the vulnerability of Mahidasht aquifer using DRASTIC, AVI and GODS in ArcGIS. DRASTIC can determine the vulnerability areas of the aquifer based on the hydrogeological properties affecting the pollution and by ranking and sum of these parameters. In the AVI, vulnerability is estimated based on two and in the GODS on four parameters. The results of the present study show that in the DRASTIC aquifer pollution potential, there is an area of 72.30 km2 with no risk of vulnerability, and an area of 266.93 km2 with very low risk, respectively. Areas with low vulnerability account for 59.69 km2 and areas with low to moderate damage account for 14.65 km2. In the AVI, vulnerability is classified into low-risk class with an area of 221.23 km2 and the average risk with an area of 208.2 km2. In the GODS, most of the area has low vulnerability with an area of 401.55 km2 and less area with medium vulnerability with less coverage of 24.2 km2. Therefore, it can be concluded that based on three evaluation models in this study, the vulnerability of Mahidasht aquifer is not high.

Sea current velocity measurement plays an important role in engineering design and measurements. Studies in the Persian Gulf and the Strait of Hormuz have conducted field studies or numerical modeling of flows in this region. In the present research, the surface currents of the Strait of Hormuz are predicted using artificial neural network approaches. In order to determine the model’s inputs, the eastern and western time series of surface currents of the strait are used, and the basins affecting the currents of this strait are identified using linear regression model. Then the neural network inputs are defined in two different cases. The first case of the time series of known basins is considered as the input of the neural network. In the other case, combinations of known time series are considered as the input of the neural network using the Jones schema. By comparing these two cases, it is concluded that the neural network model using the Jones scheme has a good performance in predicting the surface currents of this strait. In order to further investigate the neural network model, the flow data is divided into 16 different categories; so that in each category the difference between the minimum and maximum speed is 0.03 and the average of each category is considered as the output of the neural network. To determine the network inputs, the same is done for the two cases previously mentioned. In this case, the results show that the neural network model predicts surface currents with an accuracy of R = 0.85.

In coastal hydrodynamics, shore structures play an important role in changes in coastal morphology and natural current conditions in the region. Generally, the construction of structures such as piers leads to a change in the pattern of coastal currents as well as other related parameters such as sedimentation rate, turbidity, and salinity. In the present study, using field measurements and model simulation of coastal currents, the effect of Nakhle Nakhoda pier construction on the coastal flow pattern is investigated. Field velocity measurements are carried out by ADCP over a 30-day period in two depth layers. Turbidity and salinity are also collected using CTD. All the data are statistically analyzed. The results show that different parameters are affected by the change of coastal current, and the greatest effect is on turbidity. The ROMS model is used to simulate the area in two modes, with and without the pier. According to the results, the construction of this structure has caused a change in the coastline and an increase of more than 40×104 square meters to the coastal area.

Surface currents have great importance in marine studies. These currents can be an important factor in the transfer of density, nutrients or pollutants into the ocean environment. The water area of the Persian Gulf and the Sea of Oman is one of the most important waterways in the world. In this study, HYCOM current data in 2019 are used and the currents of the Oman Sea are surveyed month by month in same year, in GIS software. The strongest currents of the Oman Sea are forming in autumn and winter (in January and March). The shape of the currents is cyclic in winter and marginal and strong in autumn. The diameter of the January cycle is about 235km. The southern border current in October is about 390km and it is leaving the Oman Sea.  The highest value of velocity in the Oman Sea is 1.1m/s and the lowest value is 0.001m/s. The inflow to the Persian Gulf has less salinity and more velocity than the outflow.

In this paper, a new hydrophone sensor in low frequency is designed and simulated. The transducer mechanism is based on variation of gate source capacitor in MOSFET transistor, while the transistor gate is suspended using two beams. In response to incoming acoustic wave, gate goes under deformation and causes variation of gate-source capacitor. As a result, acoustic wave alters the drain source current of the MOSFET transistor. In contrast to previous studies, instead of using uniform rectangular gate, the comb-drive gate is used so as to increase the gate-source capacitor. First, structures and parameters such as pressure, stress and thickness of the gate are carried out. Finally, for different materials the sensitivity is calculated and compared with previous studies. By employing the finite-element-method simulation software, sensitivity and bandwidth are calculated. Simulation results indicate high sensitivity around  in low frequencies. The proposed hydrophone shows flat frequency response in rang of 10-11400 Hz.

Trinitrophenol is one of the major pollutants present in the effluents of petrochemical, oil, pharmaceutical and plastic industries, as well as in smaller amounts in municipal and agricultural wastewater. The aim of this study is to remove Trinitrophenol from aqueous solution using a modified Portunus segnis crab shell magnetic bio-composite. In order to optimize the adsorption process of Trinitrophenol, Design-Expert software and surface response method are used in the central composite design. The adsorption is evaluated by parameters of adsorbent dosage contact time (10 to 120 mins), pH (2-7), initial concentration of Trinitrophenol (10 to 60 mg / L) and adsorbent dosage (10 to 50mg). The equilibrium adsorption isotherms are analyzed using Langmuir, Freundlich and Tamkin isotherm models. The results show that under optimal conditions, the maximum removal efficiency of Trinitrophenol is attained 52% with an optimum value of pH = 3.25, the amount of adsorbent dosage is 40mg, the initial concentration of Trinitrophenol is 22.5mg per liter and the time is 92.5 minutes. Also, the study of the isotherm model show that the adsorption of Trinitrophenol on the adsorbent follows the Langmuir model with a correlation coefficient of (R2 = 86) and the maximum adsorption capacity based on the Langmuir model is 59.88mg per gr. The results of this study show that the modified Portunus segnis crab skin magnetic bio-composite has a good efficiency in removing Trinitrophenol, and at the same time its cheap price and easy access make this bio-composite to be considered a desirable biosorbent.

In Inertial Navigation Systems (INS), orientation angles are computed via integrating the gyroscopes data. Traditionally, this is done using mechanical gyros of which cost, size, and weight are the limiting factors for their utilization. However, with the advent of Micro-Electro-Mechanical-Systems (MEMS), these limitations have been mitigated significantly, to a degree that most of the modern smart phones today have these sensors onboard. Nevertheless, these sensors provide far less accuracy compared to their mechanical counterparts. Particularly, MEMS gyros collect significant amounts of accumulating error over time, which makes their results unusable after a short period of time. To overcome this problem, data from accelerometers (for Roll and Pitch angles) and magnetometers (for Yaw angle) are also utilized. These external data are fused with that of the gyros in order to control the errors thereof. But the results are vulnerable to the accelerations applied to the platform in the highly dynamic movements. In this research, a new Attitude and Heading Reference System (AHRS) is introduced which uses a complementary filter to fuse the abovementioned approaches based on their characteristics. The results from the field tests (which are conducted via smartphone data) imply that even during the roughest movements, this technique yields an accuracy of about 2 degrees for Roll and Pitch, and 4 degrees for Yaw. These numbers are very promising compared to the traditional approaches that are inferior in all situations, especially under high-dynamic movements.

Using transverse steps is a way to reduce friction resistance and also increase the velocity of stepped planing hull vessels. In stepped planing hull vessels, by increasing the velocity and entry to the planing regime and finally separation fluid flow from the step, the wetted area decreases and as a result, the drag force will decrease. In this research, an appropriate analytical method is presented to study the hydrodynamic characteristics of the stepped planing hull vessels and the results of this procedure are validated with experimental data of a specified stepped planing hull vessel for three step heights of 2, 4 and 6% of width. In the mentioned approach, using available semi-empirical relations for the geometric dimensions of the produced waves at heel of the stepped planing hull vessels, the Savitsky method is developed. The results reveal that the developed method has a much better performance compared to the Savitsky method and has an acceptable agreement with the experimental data. After validating the proposed analytical method, the effect of geometric parameters including step height, center of mass location and transvers step position on the hydrodynamic behavior of the stepped planing hull vessel is examined and the optimal value of the mentioned parameters are achieved.

In this paper, different types of SVP drifters are analyzed by using a three-dimensional computational environment to investigate the effect of geometrical characteristics of a Lagrangian drifter on its performance in the flow conditions in the Persian Gulf. By observing and examining the shape of the flow around the lateral and internal cavities of the Drago, it is concluded that the presence of cavities on the Drago causes a uniform distribution of compressive and viscous forces on the surface of the Drago. If a holeless cylinder is used as a Drago, a significant reduction in drag and slip coefficient is seen, especially at high-velocity currents. Increasing the number of holes on the Drago will not have much effect on the drifter performance and the most effective factors are changing the diameter and height of the Drago. Thus, a 30% increase in the diameter of the Drago increases the drag coefficient by 90%. In general, by examining the contour and flow velocity vector, it is found that the geometry design of Drago Drifter should be such that behind the drag, the smaller radius flow vortices are formed, and these small vortices cause uniform distribution of hydrodynamic forces on the surface of the Drago and prevent the drifter from slipping in sudden changes in current velocity.