نشریه هیدروفیزیک
سال ششم شماره 1 (پیاپی 10، بهار و تابستان 1399)

The study of sound propagation and its affective factors seems to be necessary due to the increasing applications of sound in various sciences. One of the environmental factors that influence the speed of sound is the change of current. Throughout the year, the flow of thermohaline enters the Oman Sea from the shallow inlet of the Persian Gulf, penetrating deeper into regions, causing fluctuations in temperature and salinity, resulting in reversal of sound velocity and consequently changes in characteristics. The sound in the Oman Sea extends from the Strait of Hormuz to the Indian Ocean, which varies in different years and seasons. In this study, a mathematical model was used to evaluate the effect of current change on sound propagation, and by combining the mechanical effects of eddies motion and sound propagation, a new mathematical relation was obtained to deviate sound velocity relative to angle within eddy. The path deviation of the acoustic rays is obtained after passing through the mesoscale eddies. It should be noted that for convenience, other environmental factors affecting sound propagation, including internal waves, have been overlooked. The result of the calculations shows that according to the location of sound input to the eddy range, the amount of deviation will vary with the angular velocity of the eddy and the amount of variation of the sound velocity relative to the deviation angle is obtained.

A well-known method for identifying and classifying sea and river bed sediments through acoustic instruments is based on sending and receiving sound waves to the bed. Reflected sound waves from sediments have several properties that can be used to identify and classify the type of sediment in the bed. For this purpose, in order to investigate the acoustic behavior of sediments, 4 types of sediments with different dimensions are prepared in the laboratory tank bed and then sound waves in 4 frequencies 55, 60, 65 and 70 kHz are sent from the water surface by the sound generating device and then return waves from bed sediments are recorded. In order to investigate the measured data with the type of bed sediments, the spectral power density characteristic of echoes including two periodogram and burg methods were used. In the first method, the average power parameter and in the second method, the absolute slope value parameter, between the minimum and maximum peaks, were investigated as two features to examine the relationship between data and bed material. The results indicate that these parameters have a significant relationship with the type of sediment and can be used to separate, identify and classify sediments.

Estimation of velocity distribution is one of the noteworthy challenges of water dynamics in seas and rivers. In this study, employing entropy theory and utilizing the proposed Cumulative Distribution Function (CDF), firstly, the proposed framework is proved and finally verified by experimental flume and natural rivers data. Entropy theory integrated with CDF can investigate the interrelations of physical phenomena which have a unique maximum, properly. This theory uses a global principle to conserve entropy, which is the maximization of entropy in any condition to stabilize thermodynamics systems. Furthermore, assuming velocity as a random variable leads to propose a function to estimate velocity distribution as 2D and 3D (). General Index Entropy (GIE) is used in this study and combined with proposed CDF. Comparing the proposed framework with previous methods shows that the proposed method has less sensitivity and more flexibility in estimation of parameters and significant accuracy to estimate velocity distribution. This method is applicable for maximum flow occurrence on and below the water surface.

One of the most important parameters of sea state expression are waves. It is important to know the wave characteristics for long-term process planning as well as for most inshore and offshore activities. MIKE21_SW and SWAN are two third-generation numerical wave models that have been widely used in numerical modeling for engineering applications and coastal research. In this paper, the capabilities of these two wave models in forecasting the wave characteristics at two points in the northern part of the Oman Sea are evaluated. In this regard, the data of both models are compared with field data of buoys located at these two points and the results were analyzed using statistical methods. The results show the high accuracy of these two models in forecasting wave characteristics at both points. Both models show slightly down estimated the wave height but highly correlated results with intermediate data in predicting wave height at both points. Also, the root mean square error of the results indicates the high accuracy of these two models in forecasting the wave heights.

A Magnetic Anomaly Detector (MAD) is a passive system that is used to detect vague ferromagnetic objects in the environment by detecting anomalies in the Earth's magnetic field. Detection of magnetic anomalies is an important issue in some projects, from geological surveillance to military identification. MAD sensors detect local disturbances in the magnetic field of earth, which can be used to detect the presence of hidden or immersive objects, such as submarines, land mines or naval mines and estimate their location. It is impossible to detect the acoustically quiet submarines by detectors, so it is necessary to use magnetic anomaly detection systems. In this study, the existing systems were examined and then the mechanical structure of an airborne MAD system was redesigned. In next step, the stress distribution of the designed system was analyzed. The stress analysis was performed by finite element method (FEM) using ABAQUS software. The results showed that according to the stress distribution, the maximum value of the stress for the set of parts is 88.7 MPa at acceleration 0.2 g, which is actually much less than the yield stress of the used material. As a result, there is no permanent deformation in any of the components of the system.

Statistical Energy Analysis (SEA) is a suitable method for vibro acoustic analysis of engineering models in high frequencies considering other analytical method limitations such as Finite Element and Boundary Element Methods. This method is based on averaging of acoustical and vibrational flow in subsystems. In this research, first SEA is introduced briefly and then, analysis of vibrating plate with SEA and VA One code is investigated. After verification of VA One results, acoustic performance of sonar dome in diffusion load is studied and thickness and material effects of sonar dome on acoustic pressure in specific point is investigated. The results show that acoustic performance is improved with increasing thickness in high frequencies. Also the acoustic transparency of carbon/epoxy and graphite/epoxy is averagely better than other studied materials and aluminum has better performance compared to steel and titanium.

In this paper, the applicability of the Persistent Scatterer (PS) time series analysis method is investigated in determining the rate and pattern of the area affected by subsidence in Zanjan plain in the period 2003 to 2010. The radar data used consists of two ENVISAT ASAR data sets related to the17 number of 464 descending track and 9 number of 228 ascending track, on which after processing data with Stamps Program, PS method was performed on them. After eliminating the error sources, based on the results of the time series obtained, continuous and significant subsidence were observed in this region. PS time series for track 228 specify maximum subsidence range of about 40mm/y between 2004-2010 and track 464 specify maximum subsidence range of about 35mm/y between 2003-2005. The analysis of the results with the water level information of the region over a similar time period shows a strong dependence between groundwater depletion and subsidence.

Supercavitating a hydrodynamic process in which the body is completely surrounded by a layer of gas and its formation is the result of cavitators installed in front of the body. Supercavitating vehicles can move in water bodies with high speeds and thus significantly reduce frictional resistance. One of the most cavitators used in practical applications is perforated disk-shaped cavitator, which is analyzed in this article. Sensitivity of geometrical and flow parameters and their impact on the geometry of the cavity (bubble) and the rate of mass transfer, are the most important variables which have been discussed in this study. Numerical analysis has been performed using computational fluid dynamic based on finite volume method with the help of Ansys-Fluent software. The k-ε model is used to model the turbulent fluid flow. The generated network is structured around the cavitator and across the entire network solution domain. To validate the numerical results, two geometries including a rectangular surface with attack angle of 10 degrees and disk cavitator have been used. According to the obtained results, there is good agreement between numerical and experimental data. Based on the obtained results for speeds higher than 60 meters per second, using constant correction factors, the resistance level of the super-cavitation bubble can be accurately estimated.

By increasing the complexity of products and systems, the use of preventive maintenance and repair systems, such as repairability in the design of the system, can play an important role in reducing the finished product costs. In this paper, attention is paid to the reliability of designing systems of a navy in the form of a native pattern in the context of the design life of the systems, improving the maintainability of the systems and reducing the stopping time for maintenance in the production of products and improvement of reliability and availability of systems is being investigated when necessary. To achieve the above, due to the diminutiveness of the issues of maintainability in the design of marine systems, after reviewing the life cycles of similar products and selecting the most appropriate marine life cycle, which includes 5 main phases, and the use of 16 maintainability requirements, and by the aid of multi-criteria decision-making method, design pattern and development requirements for lifecycle-based lifecycle are extracted from the design of marine systems. Reduction of the costs and time of the note, increase in system availability, reduction of the damage/fatigue of the technical operator, reduction of the training hours of technical operators, improvement and expedition of the diagnosis, reduction of the probability of damage to the part or system and product, and improvement of reliability are among the benefits of using this template in design.

Optimal determination of material constants of behavior criteria with minimal number of experimental test data is of interest to designers. Khan-Liu yield/fracture criterion is one of the comparatively accurate and user-friendly criteria to predict behavior of alloys such as Ti-6Al-4V alloy. This criterion with ten constants can take into account effects of parameters such as asymmetry in tension and compression, anisotropy, hydrostatic pressure, strain rate and temperature as uncoupled. Evolutionary algorithms are optimally suitable methods for determining the materials behavior equations constants. In this article, the genetic algorithm and particle swarm optimization methods are used to determine the material constants of Khan-Liu criterion. Experimental results of uniaxial tension and compression tests in two directions, rolling and transverse direction of Ti-6Al-4V sheet, at different temperatures with 1 sec-1 strain rate are used. From these data equal-biaxial points were calculated. After applying two algorithms on these data, results showed that particle swarm optimization is better than genetic algorithm. Therefore, this method is suggested to determine the constants of this criterion. The material constants extraction methodology with two genetic algorithm and particle swarm optimization, as well as aspects of the development and improvement of Khan-Liu criterion are results of this paper.

Today Special vessels are used to monitor the underwater environmental conditions and the bed of the seas and oceans. Such vessels are designed and used in different ways. One of these types of vessels is the sea-glider. The body shape of sea-gliders varies based on operating requirements and environmental conditions. They are designed to have very low energy consumption due to the lack of a propeller propulsion system, so they can perform their mission underwater for a long time. These gliders are usually designed to have a floating system, fixed wings, internal moving objects, a ballast pump and a rudder. Therefore, the downward and upward movement of these gliders is controlled by the movement of its internal objects back and forth and its vertical movement (height and depth change) is controlled from floating change from negative to positive and vice versa. Numerical analysis of these gliders is very practical and important in order to better understand the motion control and maneuverability. This paper examines the lift and drag coefficient of a sea-glider at different angles of attack in which fixed blocks play a major role. The study of these coefficients and their changes, which are the main hydrodynamic parameters, have a great impact on how to improve the motor performance and maneuverability of gliders. The glider studied in this paper is Sea-glider, which underwater performance, geometric model in Katia software, static model and numerical analysis in Ansys- Fluent software is done and finally the obtained results are validated with testing results of the model in the towing tank. The analyzes were performed at different angles. At zero-degree angle, the maximum pressure point or stagnation point at the tip of the nose in front of the sea-glider is 2.30 Pascal. The lowest pressure and maximum fluid velocity occur at the junction of the wings to the body and its curvature. The error rate of numerical results compared to experimental results is about 30%, which is reasonable compared to similar studies.

In recent years, the conical shells under external pressure are widely used in construction of the under-water pressure hulls, covers of aero-engines and storage tanks. Strength of thin-walled shells under external pressure are usually influenced by the buckling phenomenon. So, its study is in high degree of importance. The buckling analysis of thin conical shells based on theoretical and experimental methods is accompanied by shortcomings such as time consuming and complexity. In this paper, an efficient method based on Artificial Neural Network (ANN) is presented for prediction of buckling and post-buckling behavior of conical shells. Primarily, the linear and non-linear buckling loads of the truncated cones with various thickness and stiffener dimensions are obtained by using the Finite Element (FE) analysis. Then, these obtained results are submitted to the Neural Network for training. In order to verify the solution procedure, the predicted results of ANN are compared with those of extracted from FE analysis. It is shown, that the predictive model benefits from high convergence and accuracy. Finally, some predicted results of buckling and post-buckling analysis of conical shells is figured.