فصلنامه علوم و فناوری دریا
سال بیست و دوم شماره 88 (زمستان 1397)

The Scaled Boundary Finite Element Method (SBFEM) is a rather new semi-analytical method that combines the merits of finite element and boundary element methods. The SBFEM method uses weighted residual technique and finite elements to weaken and discretize the governing differential equation only on the boundary of the problem and then solves the resulted system of weakened ordinary differential equations in the radial direction, analytically. In this article, the boundary-value problem of water wave diffraction by a vertical circular cylinder has been solved by SBFEM method. Only the circular boundary is discretized with one-dimensional finite-elements. The governing partial differential equation is transformed to a system of ordinary differential equations, whose numerical solution on the nodes of circular boundary is obtained with the aid of analytical solutions that satisfy the far field boundary condition. The comparison of hydrodynamic parameters such as total velocity potential, wave elevation and horizontal component of wave excitation force with those obtained from analytical and other numerical methods shows high accuracy and efficiency of the present SBFEM method.

This paper presented the strategy of supply and control of power required at submarines using battery and super-capacitor. A design is presented to optimize the required power of this system which provides electricity for submarine by high level of reliability. For this purpose, dynamic model of the system has been considered including fuel cell, dc-dc convertor (to stabilize the link voltage), and battery. Also, dynamic model of a super-capacitor connected parallel to convertor for entering at start point of the system to support fuel cell and battery increase rippling quality of dc wave because of high performance and speed of current injection is proposed. Simulation result indicated that by using super-capacitor the voltage sag is decreased.

To analyze the behavior of fluids around obstacles cylinder to reduce costs, reduce the time to achieve the results and analysis of boundary conditions to the numerical simulation using FLUENT software Rvym.dr paper, Unsteady Flow, two-dimensional, incompressible intended for each Reynolds static pressure contours, Vorticity, flowing lines and speed has been obtained.It can be seen that the rectangular cylinder pressure at the inlet of the circular cylinders and more triangular and wherever is made of vortices And in which the pressure Darym.dr least the low pressure flow lines will be able to lose your makeup.Also generally at high Reynolds numbers for all cases, and in this case also during the more turbulent flow vortices more.The main gates of the high-pressure occur at these points there is no vortices and flow irregularities.It is known that the contours pressure cylinder with a rectangular cross-sectional area drag to endure more.

Direct torque control (DTC) is one of the most effective methods for controlling the induction motor. In direct torque control, motor flux and torque are considered as reference quantities, and are controlled by optimal selection of inverter switching vectors. Using the direct torque control method, you can reduce the field oriented control (FOC) constraints and complexities. The direct torque control has a very fast torque response and is resistant to sudden load variations. In this paper, a complete comparison was made between two methods of classic direct torque control (DTC-CLASSIC) and direct torque control based on space vector pulse width modulation (DTC-SVPWM) using two-level and three-level diode clamp inverters (NPC). Comparison of these methods was carried out using simulation results in MATLAB software. The results of the simulation show that, with respect to the limitation constraint of maximum switching frequency, the DTC-SVPWM applying three-level inverter has less flux and torque ripple and less THD of stator current than the other three.

Increasing number of vessels with various capacities, leaded to a sky rocketing demand for the construction of vessel repair and maintenance facilities. Ship slipway is among one of this category. In relation with slipway construction, accurate initial estimation of slipway dimensions and also, its final cost is of great importance; as the construction of slipways costs too much. This study aims at investigation of requirements and formulae for the initial dimensions of the slipway i.e. length, width, maximum capacity, angle and so on. Appropriate estimation of slipway dimensions is vital for the decision makings during pre-designing of such projects to reduce the capital and operational costs.

The purpose of this study is the use of stable isotopes in the analysis, analysis and description of the aquatic food web. Sustained isotopes, as the strongest natural tracer, carry vital and valuable information and are used in environmental studies due to their high resistance and long half-lives. The most important isotopes of the elements are H-O-N-C in the aquatic environment. Most isotopes are measured by mass spectrometers. Measurements show that the frequency of isotopes is not the same in nature. The aquatic food network is the result of the interference of food webs between organisms and its sustainability is defined by the ecosystem structure. Sustained isotopes are an effective and effective means of identifying the relationship between primary producers and end users of the food web and defining nutritional patterns, distribution and migration of aquatic organisms

this research follow to answer this question: how much Iranian shipping company familiar with requirements of commercial documents for transportation?. ref to the question, the paper has application nature and in terms of methodology it is a survey-descriptive research. after study of literature review, questionnaire developed to answer research question. it consist of 3 general and 10 specialized questions. use opinions of 100 person of sell and document experts of shipping company in forms of questionnaire. Smirinov test result show data is parametric and to analyses of questionnaires show used T test. findings of research show these shipping company familiar with 6 of 10 documents.

The research is aimed at a comparative study of the coverage of the IRAN, DOCHEWELL and the BBC news agencies on the Sunni tanker tanker accident in the period from January 16 to 25, 2018. In this research, quantitative and qualitative content analysis method has been used. The purposeful sampling of the type of consecutive days is census and its unit is "news". Validity (Validity) Measurement has been achieved with the "parallel credit" criterion and through the re-control of two experts. The reliability of the research and coding method was obtained using the Kappa formula in SPSS software, which indicates the reliability of the research. Also, descriptive measures (frequency, proportion, etc.) were used to analyze the data. Chi-square test was used to analyze the relationship between the reported information and the visually impaired audience.According to the study, the news coverage of the Sanchez oil tanker incident in the IRNA news agency was higher in comparison with the BBC and DOE news agencies and used the highlighting technique; the suggestion of IRNA news was positive and was almost neutral in foreign news agencies.