فصلنامه دریا فنون
سال سوم شماره 1 (پیاپی 5، بهار و تابستان 1395)

Due to the very close physical properties of real targets and clutter of active sonar, the separation of these objectives is the latest challenge to researchers and industrialists of the acoustic field. Multi-Layer Perceptron (MLP) is one of the most widely used Neural Networks (NNs) for classification purposes in the real world. Training is an important part of these NNs and recently becomes attractive for many researchers. For training MLP NNs, the recurrent and gradient descent methods have always been used. Poor classification accuracy, trapped in local minimums and low convergence speed are the disadvantages of traditional methods. To overcome these disadvantages, in recent years the use of heuristic and meta-heuristic algorithms have become very common. This paper presents a hybrid optimization algorithm of Particle Swarm Optimization and Gravity Search Algorithm (PSOGSA) for training MLP networks. GSA, a new meta-heuristic optimization method, is based on the interaction of gravity and mass. It has been proven that this algorithm has good ability of global search, but it suffers from slow searching speed in the last iterations. This article uses PSOGSA according to the unique ability of PSO on the operational phase of the hybrid method to solve the above problems. The results show that the classification methods based on GSA, PSO and PSOGSA, classify sonar dataset with the accuracy of 92.7500, 93.6741 and 94.42308. The hybrid algorithm convergence speed is better than other two standard algorithms.

In positioning, Gradient Steepest Decent algorithm is used as an iterative method and based on TDOA. This algorithm is designed in the Cartesian coordinates. Given that resources are mainly in the form of latitude and longitude coordinates, Its conversion to Cartesian coordinates is in error. On the other hand, this algorithm requires much number of iterations to convergence towards the desired response, in WGS84 coordinates. In this paper, therewith that the Gradient Steepest Descent algorithm is designed in WGS84 coordinates, performance of this algorithm in terms of error rate and the number of iterations required to achieve the desired accuracy are compared in Cartesian and WGS84 coordinates. Then a way to reduce the iterations and decrease the waste of time is proposed in combination of two coordinates. The root mean square errors of all these methods are compared with each other.

Parameters of fuel injection system, play an important role in the combustion process and, consequently, fuel consumption and emissions output. Therefore, in this study, the effects of various parameters such as Injection timing, injection during, the geometry of the injector, (the injector orifice diameter), Spray cone angle and fuel injection pressure on the performance and emissions of a DI marine diesel engine have been investigated. To evaluate the results of simulation, the maximum In-cylinder pressure has been compared with experimental data. In addition to this parameter, the experimental values of NOx, soot and brake specific fuel consumption (BSFC) have been compared with simulated results. The results of simulation show that the good agreement with experimental data.

Hydrodynamic coefficients for an autonomous underwater vehicle (AUV) are obtained by simulating the maneuver tests in computational fluid dynamic (CFD) media. The simulations are performed for different length to diameter ratios by STAR-CCM software. Also the effects of different hydroplanes as a hull appendage is investigated. Hydrodynamic forces and moment are computed and by using suitable curve fitting linear and nonlinear hydrodynamic coefficients are calculated. The results show that by increasing the length to diameter ratio the higher hydrodynamic coefficients can be obtained. The comparison of simulated results with the available experimental data shows a very good agreement among them.

Calculations of resistance and powering are very important in floating vehicle design. Because of limitations of architecture and alignment, these calculations are more important in underwater vehicle design. This paper researches the powering calculations of an AUV . Initial describe the empirical formulas for calculations of submersible vehicle, then simulated the stream around of AUV with its propeller by CFD method to estimate the resistance and required power. Practical test and experimental work have been done for calculate of power and efficiency of the floating devices. The analysis result and experimental work have been described. Finally, the power that calculated by CFD and empirical methods is verified by experimental method and represented the amounts of error.

Sea states are usually obtained using wave buoys. Wave recording using these wave buoys is usually associated with some errors. So before extracting any information from this data it is necessary to identify and remove or correct them. The aim of this paper is identifying the errors in wave records of buoys using local outlier factor (LOF) method. LOF is a powefull method to identify anomalies in the data in machine learning which is used in many practical applications. In this paper the daily wave data of Asalouye of Boushehr Province in persian Gulf recorded by PMO buoy in the period 17/02/92 to 01/05/92 was analysed for errors using this method. The results show that LOF is an efficient method to detect errors in wave data loggers.

Occurrence of water scouring phenomenon around hydraulic structures is one of the most essential factors that destroys and consequently losses of the financial each year. Existence of pier structure in front of the entrance of harbor, causes to generate three dimensional (3-D) flows around the piles of piers (due to entrance of wave into the harbor and the result of ships movements) and causes erosion, sedimentation of basin and localized water scouring. In numerical modelings that have been done so far, rate of water scouring is a function of flow parameters such as flow velocity, depth and geometrical parameters like diameter of the piles and granulation. In this paper, in addition to the study of previous parameters, we can estimate amount of affect of rotation in water scouring process around the piles of piers. In this article, according to the existence of 3-D flows around hydraulic structures such as downwards flows in front of piles and in order to consider the role of flows in water scouring a complete 3-D model is used for hydraulic flow simulation around the structures. To consider the actual boundaries of the piles of piers, the structural mesh and curvelinear border method (along the horizontal and vertical) is used. Due to changes in depth and sea bottom, the Sigma coordinate system is used to mesh.

Numerical simulation of nonlinear waves is of prime importance. In this research the WISE 2DV numerical model has been deployed. In the WISE model Reynolds-averaged Navier-Stokes (RANS) equations have been solved using finite volume discretization and projection method. The method of volume of fluid for surface has been implemented in the model. For implementation of VOF method, Youngs scheme has been utilized. In this scheme color function advection is based on piecewise linear interface reconstruction. The k–ε model is used for turbulence closure of RANS equations.
For validation of the model a short amplitude sloshing wave in a tank, regular wave in a flume and propagation of solitary wave have been simulated, and the results have been compared with analytical solutions, which show very good agreements. A non-linear short wave propagation has also been simulated, and predictions have been compared against experimental results, which confirms the model ability in prediction of non-linear short waves.

Results of the field measurements using CTD profiler in the southern coastal waters of the Caspian Sea are presented. The measurements were carried out in Kiyashahr region that is located in the Guilan province, in north of Iran. The observations were done over 13 sampling station with a maximum depth of 90 m depth during a marine cruise in the southern coastal waters of the Caspian Sea. During the marine cruise, CTD probe was released into the seawater column from sea surface to the bottom near 90 m depth. The collected data showed formation a seasonal thermal stratification including surface mixed layer, Thermocline and deep water layer in the water column. Water temperature in the sea surface mixed layer (with 10 m depth) ranged between 29.5-29 oC. At the time of measurement in midsummer, thermocline layer had 30 m thickness and located between 10-40 m depths. Vertical structure of sea water temperature indicated a sharp vertical gradient 20oC across the thermocline. Below the thermocline till sea bottom, seasonal variations of temperature were slight.